Social support as a predictor exhaled nitric oxide in healthy individuals across time

International Journal of Psychophysiology 93 (2014) 356–362

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Social support as a predictor exhaled nitric oxide in healthy individuals across time Ana F. Trueba ⁎, David Rosenfield, Noelle Bassi Smith, Tabitha L. Gorena, Thomas Ritz Department of Psychology, Southern Methodist University, Dallas, TX, USA

a r t i c l e

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Article history: Received 15 January 2014 Received in revised form 20 May 2014 Accepted 21 May 2014 Available online 29 May 2014 Keywords: Nitric oxide Social support Depression Stress Negative affect Health

a b s t r a c t Psychosocial factors such as social support and depression have long been associated with health outcomes. Elevated depressive symptoms are usually associated with worse health outcomes, whereas social support has been related to improvements in health. Nitric oxide levels are an important marker of both cardiovascular health and immune function. Research suggests that exhaled nitric oxide is affected by stress, negative affect, and depression; however, the effect of social support has not been previously explored. Thus, we sought to examine the association of social support, negative affect, and depression with exhaled nitric oxide in a group of 35 healthy individuals (10 males and 25 females) with a mean age of 20.5 years across five weekly assessments. Results showed that changes in social support within individuals were positively associated with levels of exhaled nitric oxide independent of other psychosocial factors. Further exploration of the health implications of this positive relationship between airway nitric oxide and social support is necessary. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Psychosocial factors have long been found to be related to changes in immune markers (Glaser et al., 1992; Herbert and Cohen, 1993; Yang et al., 2007) and disease processes relevant to many medical conditions (e.g. cardiovascular disease, Eller et al., 2009; Frasure-Smith et al., 2000; Pratt et al., 1996). Recently, nitric oxide (NO) has been added to the list of important biomarkers involved in various aspects of health (Pacher et al., 2007; Sessa, 2005) and pathophysiology (Stefano and Esch, 2005). Reductions in exhaled NO have been associated with pulmonary hypertension (Hare et al., 2002; Kaneko et al., 1998; Ozkan et al., 2001) and atherosclerosis (Salonen et al., 2012). There is also evidence that NO can protect the airways from infection by neutralizing pathogens (Bogdan, 2001; Ricciardolo, 2003). It is possible that NO provides an additional pathway linking psychological factors and certain medical conditions (Le Mellédo et al., 2004), yet this has been largely unexplored. Psychological factors such as stress and depression have been associated with altered NO levels. NO derived from polymorphonuclear cells can be reduced in depression (Srivastava et al., 2002) and higher Abbreviations: PSS, Perceived Stress Scale; MSPSS, Multidimensional Scale of Perceived Social Support; PANAS-NA, Positive Affect Negative Affect Schedule, negative affect subscale; HADS-D, Hospital Anxiety and Depression Scale, depression subscale; HADSA, Hospital Anxiety and Depression Scale, anxiety subscale; FeNO, Fraction of exhaled nitric oxide. ⁎ Corresponding author at: 6116 N. Central Expressway, Dallas, TX 75206, USA. Tel.: + 1 214 768 1768; fax: + 1 214 768 3910. E-mail address: [email protected] (A.F. Trueba).

http://dx.doi.org/10.1016/j.ijpsycho.2014.05.011 0167-8760/© 2014 Elsevier B.V. All rights reserved.

depressive symptoms have been associated with lower NO levels in exhaled air (Trueba et al., 2013) and serum (e.g., Chrapko et al., 2004; Selley, 2004). In addition, reduced airway NO has been observed during final academic exam periods compared to low stress periods in healthy individuals (Höglund et al., 2006; Trueba et al., 2013). In contrast, Ritz et al. (2011) found that, in both healthy and asthmatic participants, acute psychosocial laboratory stress led to an increase in airway NO at the point when cortisol was the highest after stress, whereas Chen et al. (2010) found elevations of airway NO following a stressful interview in asthmatic children with low socioeconomic status. Another study found that higher momentary negative affect was related to greater airway NO levels; in contrast, daily hassles in the previous three months were related to lower airway NO in asthma patients but not in healthy controls (Kullowatz et al., 2008). Taken together, these findings suggest that the relationship between psychological factors and NO may differ depending on the psychological construct that is examined. Momentary negative affect and acute stress are associated with higher NO, whereas depression and prolonged stress appear to show the opposite relationship, thus emphasizing the need for further investigation (for review, see also Ritz and Trueba, 2014). Although NO has been linked to a number of psychological factors, to our knowledge, no study has examined the effect of social support. Social support can impact physiological pathways that confer health benefits. Several studies have shown that social support is related to reduced mortality and morbidity rates (Uchino, 2006). There is evidence to suggest that social support has a positive effect on cardiovascular, immune and neuroendocrine systems (Uchino, 2006). Indeed the results of meta-analysis found that social support had a positive

A.F. Trueba et al. / International Journal of Psychophysiology 93 (2014) 356–362

effect on several physiological measures related to health (heart rate, systolic blood pressure, diastolic blood pressure, skin conductance, and cortisol) (Thorsteinsson and James, 1999). Studies have also found a positive association between social support and healthy immune function. More specifically social support has been positively associated with immunoglobulin production (antibody titers) in response to certain vaccines (Glaser et al., 1992), while other studies have found a negative association with systemic inflammatory markers, such as interleukin 6 (IL-6; Friedman et al., 2005; Lutgendorf et al., 2000). Higher social support has been found to attenuate the relationship between depression and mortality related to cardiac events (Frasure-Smith et al., 2000). There are also suggestions that the effect of social support on health-related biomarkers is not dependent on stress (Lutgendorf et al., 2005) or depression (Baron et al., 1990). Despite the evidence for a relationship between social support and a multitude of health markers and processes, the association between social support and NO has not been previously examined. To date, most studies have examined the association between psychological factors and NO cross-sectionally, thus little is known about the temporal relationship between psychological factors and NO. In this study, we aimed to examine the relationship between airway NO, measured by the fraction of nitric oxide in exhaled air (FeNO) and a number of psychological factors, including social support, depression, negative affect, anxiety, and perceived stress, across multiple weeks in healthy individuals. The multiple time points in this study would enable us to also examine within-individual associations of psychological factors and FeNO. Measurements of FeNO are a non-invasive method to capture NO produced from various cells in the lung tissue. FeNO levels have been found to be associated with a range of medical conditions, including asthma (Harkins et al., 2004; Ricciardolo et al., 2004), allergic rhinitis (Gratziou et al., 2001), and cardiovascular disease (Hare et al., 2002; Kaneko et al., 1998; Ozkan et al., 2001). The interpretation of airway NO is complicated by the fact that NO can originate from a number of sources. NO is formed as a product of NO synthase (NOS) enzymes, which are manifested either in constitutive form (cNOS) including neuronal and endothelial NOS, or in inducible form (iNOS). Inflammatory processes are usually associated with an increased production of iNOS, which leads to a much greater expression of NO that can have a cytotoxic effect (Esch et al., 2002). However, NO from cNOS activity is known to confer beneficial effects, such as vasodilation (Arnal et al., 1999), bronchodilation (Belvisi et al., 1992), and bronchoprotection (Ricciardolo et al., 1996). Studies have varied in that they have attributed FeNO levels in healthy individuals mainly to cNOS activity (Yates et al., 1996) or iNOS activity in the airway epithelium, which also serves as a defense against pathogens (Abba, 2009). In line with an interpretation of NO as conferring health benefits, we expected that social support would be positively associated with FeNO, such that participants reporting higher social support would also display higher FeNO. In addition, in agreement with previous findings (Trueba et al., 2013), we also expected to replicate earlier associations of negative affect, anxiety, and depression with FeNO levels. 2. Methods

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participants, and the study was approved by the local institutional review board. 2.2. Exhaled nitric oxide (FeNO) We used a hand-held electrochemical analyzer (NIOX mino, Aerocrine, Solna, Sweden; Alving et al., 2006) to determine FeNO (in ppb). Research shows that FeNO levels obtained from this portable instrument are comparable to those from the standard stationary device (Alving et al., 2006; Pisi et al., 2010). Measurements were performed in accordance with American Thoracic Society and European Respiratory Society (2005) guidelines. In order to close the velopharyngeal aperture, an exhalation was performed against a stable resistance at a rate of 0.05 L/s for a duration of 10 s. Participants were instructed not to eat 2 h prior to assessments in order to avoid the influences by nitrate-rich foods. Exercise or heavier physical activity was also discouraged during this time, as they have been shown to attenuate FeNO levels (Lim and Mottram, 2008). 2.3. Self-report measures 2.3.1. Social support Social support was measured with the Multidimensional Scale of Perceived Social Support (MSPSS; Zimet et al., 1990). The 12 items were rated on 7-point scales, from 1 = very strongly disagree to 7 = very strongly agree, resulting in a possible overall score that ranged from 12 to 84. This measure can be divided into 3 subscales that each captures a distinct source of social support: Family, Friends, and Significant Others. Their subscales are comprised of 4 items each and their sum scores can range from 1 to 21. 2.3.2. Depression and anxiety The Hospital Anxiety and Depression Scale (HADS; Zigmond and Snaith, 1983) was used to assess depressive mood (HADS-D) and anxious mood (HADS-A) in the past week. The highest score that can be obtained in the 7-item depression and anxiety subscales is 21. Scores ranging from 8 to10 are deemed as possibly indicative of clinical problems, whereas scores between11 and 21 are “probably clinical” (Zigmond and Snaith, 1983). 2.3.3. Negative affect The negative affect subscale of the Positive Affect Negative Affect Schedule (PANAS-NA; Watson et al., 1988) was used to assess current state negative affect. This scale consists of 10 items rated on 5-point scales from: 0 = very slightly or not at all to 4 = extremely, resulting in a highest possible score of 40 and lowest possible score of 0. 2.3.4. Perceived stress In order to capture participants' perceived stress, we used the 10item Perceived Stress Scale (PSS; Cohen et al., 1983), which provided a measure of participants' stress across the previous month. This measure was given at the last assessment in order to capture stress in the month in which participants were assessed weekly. Each item was rated on a 5point scale that ranged from 0 = never to 4 = very often, so that the highest possible total score was 40 and the lowest 0.

2.1. Participants Undergraduate students taking psychology courses were recruited for this study. Participants had to be able to complete all of the physiological assessments and were excluded if they reported smoking or medical conditions that are related to changes in FeNO levels, including allergies, asthma, and any severe heart conditions, such as angina, myocardial infarction, congestive heart failure, and transient ischemic attacks, among others (Esch et al., 2002). Furthermore, participants who used corticosteroids (oral or injected within the past six weeks) were also excluded. Written informed consent was obtained from all

2.3.5. Respiratory symptoms Participants' respiratory symptoms were assessed with 3 items: chest tightness, short of breath, and rapid breathing. Each item was measured with a 10-point scale ranging from 1 = not at all to 10 = extremely. 2.4. Procedure Participants came to the laboratory for five weekly sessions. Sessions were conducted on the same day of the week and at the same time of

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day every week for each participant. This helped control for diurnal effects on participants' FeNO. Prior to every session, participants were asked to refrain from drinking or eating anything for 2 h except for water and to avoid any vigorous physical activity 2 h prior to the session. In the first session, participants' consent was obtained. In each session, participants were first asked to perform the FeNO measurement. Finally, participants filled out a questionnaire battery at a computer terminal. Upon completion of the fifth visit, participants were debriefed. They were compensated with course credit points for their participation. 2.5. Data analysis Prior to all analyses, descriptive statistics were calculated. Multilevel modeling (MLM) was used for the main analyses, with repeated measures of the data nested within individuals. MLM allows inclusion of all subjects regardless of missing data and can flexibly model the error variance of the repeated measures. We employed maximum likelihood estimation, an auto-regressive error covariance matrix, and used the Satterthwaite approximation to calculate degrees of freedom for significance tests for the regression coefficients. Cohen's d effect sizes were calculated using the t-statistic to Cohen's d transformation. Over the course of the study, some participants missed some assessments, resulting in 20.0% missing data, but because MLM includes all participants regardless of missing data, no participant was dropped from the analysis because of missing data. Similar amounts of missing data were reported by other studies of social support on health (Appleyard et al., 2007; Carpiano, 2007). In our initial analysis, social support, negative mood, anxiety, and depressive symptoms were modeled as level-1 predictors of FeNO since they were measured at each assessment. Stress was modeled as a level-2 predictor of FeNO because it was measured only once (at the end of the study). Three control variables were also included in the analysis: respiratory symptoms (measured at each assessment and hence a level-1 predictor) and age and gender (level-2 predictors; see Table 2 for the list of variables in the model). In our second analysis, we investigated the nature of the relation between the level-1 (repeatedly measured) predictors and FeNO. Hedeker and Gibbons (2006) have shown that variables that are measured repeatedly over time are comprised of a between-individuals component and a within-individual component, as indicated by the following formula: Xij ¼ Xmeani þ Xdeviationsij where Xij is the value of a predictor X for individual i at time point j, Xmeani is the mean of X for individual i over all the time points, and Xdeviationsij is the difference between the value of Xij at assessment j and the mean of X across all assessments for individual i. This formula parses each assessment of X into a between-individuals (Xmeani, the Table 1 Descriptive statistics of variables for N = 35 healthy participants.

PSS MSPSS PANAS-NA HADS-D HADS-A FeNO (ppb)

Possible range

Minimum

Maximum

Mean

Standard deviation

0–44 12–84 0–40 0–21 0–21

2.0 13.0 0.0 0.0 1.0 5.0

30.0 77.0 11.0 16.0 17.0 94.0

18.6 63.3 3.3 3.7 6.8 20.5

7.7 13.4 3.1 3.6 3.7 16.9

Note: PSS = Perceived Stress Scale, MSPSS = Multidimensional Scale of Perceived Social Support, PANAS-NA = Positive Affect Negative Affect Schedule, negative affect subscale, HADS-D = Hospital Anxiety and Depression Scale, depression subscale, HADSA = Hospital Anxiety and Depression Scale, anxiety subscale, and FeNO = Fraction of exhaled nitric oxide. Values of participants at the first of the 5 weekly assessments, except for PSS, which was measured only at the last assessment, retrospectively covering the previous 4 weeks.

Table 2 Results of multi-level modeling analysis testing the association of psychological factors with FeNO. Overall analysis Between/within analysis Predictor PSS HADS-D HADS-A MSPSS PANAS-NA Gender Age Respiration symptoms

Between component Within component 0.006 0.013 −0.005 0.011⁎⁎⁎ −0.003 0.638⁎⁎⁎ −0.032⁎ −0.013

0.005 0.009 0.031 −0.002 0.029 0.649⁎⁎⁎ 0.027+ −0.030

– 0.014 0.008 0.015⁎⁎⁎ −0.005 – – 0.003

Note: A “–” under the Within Component indicates that no within-individual variance component was tested since these variables did not change across assessments. + p ≤ .10. ⁎ p ≤ .05. ⁎⁎ p ≤ .01. ⁎⁎⁎ p ≤ .001.

mean level of X for individual i) and a within-subjects component (Xdeviationsij, the deviations of X at each assessment from its average across the assessments). This analysis allows us to break down the results of the above overall analysis to examine the extent to which the between-individuals effects as opposed to within-individual effects account for the overall relations between our predictors and NO. Xdeviationsij over time are modeled as a time-varying predictor of outcome in level 1 of the MLM. Xmeani, on the other hand, is as an individual level variable, modeled in level 2 of the MLM. The mean and deviations of all of our predictors that were measured over time (social support, negative mood, HADS-A, and HADS-D) were included in the MLM model predicting FeNO, along with average stress level and the three control variables: gender, age, and respiratory symptoms (see Table 2 for the list of variables in the model). In this model, the deviation scores reflect the relation between the predictors and FeNO within individuals, over time, while the mean scores reflect the between-individuals relation between average levels of each predictor for each individual with average levels of FeNO. In a subsequent model, we also controlled for menstrual cycle and birth control use in female participants only. Because previous research suggests that social support could moderate the relation between perceived stress and FeNO, we conducted an additional analysis including the interaction of social support with each of the other psychological predictors. Non-significant interactions were then dropped and the final analysis was recomputed. We used the approach suggested by Aiken and West (1991) to decompose these interactions. This approach uses all the data in the sample to provide model based predictions of the relation between perceived stress and FeNO at high social support (1 SD above the mean of social support) and at low levels of social support (1 SD below the mean of social support). We also explored this interaction from the other perspective in which we examined the relation between social support and FeNO at high levels of perceived stress (1 SD above the mean of perceived stress) and at low levels of perceived stress (1 SD below the mean of perceived stress). 3. Results 3.1. Participant characteristics at first assessment Our total participant sample consisted of 35 psychology students (10 males and 25 females). The mean age was 20.5 years (SD = 5.4). Participants reported the following racial backgrounds: 57.1% Caucasian Non-Hispanic (n = 20), 8.6% Caucasian Hispanic (n = 3), 8.6% Asian (n = 3), 5.7% African American (n = 2), and 20% listed their race as “mixed” or “other” (n = 7). Table 1 shows the means of main predictors for the first visit.

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3.5. Exploratory analyses

3.2. Overall associations of FeNO with social support and other psychosocial variables The MLM analysis showed that higher levels of social support were associated with higher FeNO, b = 0.011, t(97) = 3.06, p = 0.003, and d = 0.62. None of the other predictors (negative affect, anxiety, depression, and perceived stress) were related to FeNO (ps N .311). This analysis also showed that males had higher FeNO than females, b = 0.639, t(40) = 3.85, p b 0.001, and d = 1.22, and younger participants had higher FeNO than older ones, b = −0.032, t(38) = −2.33, p = 0.026, and d = 0.76. 3.3. Analysis of within- and between-individual associations of FeNO with social support and other psychosocial variables Using the MLM model which disaggregates the between-individuals and within-individual effects of the predictors of FeNO, we found that increases in social support were associated with higher levels of FeNO within the individual, over time, b = 0.015, t(73) = 3.50, p = 0.001, and d = 0.82. There were no other significant associations between FeNO and any of the other within-individual predictors (ps N 0.326). Also, none of the relations between FeNO and the between-individuals predictors were significant (ps N 0.346). 3.4. The association of FeNO with the interaction between social support and other psychological variables To determine if perceived stress moderated the effect of our psychological variables on FeNO, we added the interactions between stress and each of our psychological variables (social support, negative affect, depression, and anxiety) to our first, overall MLM model. Nonsignificant interactions were then dropped and the model was recomputed. Our final model revealed a significant Perceived Stress × Social Support interaction, b = − 0.001, t(114) = 2.29, p =0.024, and d = 0.43. We found that for participants with high social support (1 SD above the mean [SS ≥ 75]), stress was not at all related to FeNO, b = − 0.006, t(58) = − 0.47, and p = 0.639. For participants with low levels of social support (1 SD below the mean [SS ≤ 55]), stress was also not significantly related to FeNO, but the relation was slightly positive, b = 0.013, t(57) = 1.07, and p = 0.291. Exploring the interaction from the other perspective (perceived stress moderating the effect of stress on FeNO), we found that for those reporting high levels of stress (PSS ≥ 24), social support was not related to FeNO, b = 0.002, t(104) = 0.35, and p = 0.730. On the other hand, for those reporting low levels of stress (PSS ≤ 10), social support was highly related to FeNO, b = 0.016, t(59) = 3.89, p b 0.001, and d = 1.00 (see Fig. 1).

Log (FeNO)

Social Support and FeNO at High and Low PSS 4 3.8 3.6 3.4 3.2 3 2.8 2.6 2.4 2.2 2

High PSS Low PSS

15

30

45

60

359

75

Social Support Note. The y axis represents log(FeNO) and not raw FeNO values. Fig. 1. The relationship between social support and FeNO at high and low scores of the Perceived Stress Scale (PSS). The y axis represents log(FeNO) and not raw FeNO values.

We also investigated whether any of the three subscales of the MSPSS (support from Family, Friends, or from Significant Others) were particularly related to FeNO. We replaced the MSPSS total score in our first MLM model with the three MSPSS subscales. Although the subscales as a group were significantly related to FeNO, χ2 (3) = 15.60, p = 0.001, none of the individual scales was significantly associated with FeNO over and above the others (ps N 0.222). Findings from the two MLM analyses did not change when we excluded social support, nor when we excluded the one female participant who had very high values of FeNO compared to healthy standards (94 and 202 ppb for the first two assessments in which she participated). We also reran the model for females only, including menstrual cycle phase and use of birth control included as covariates, and their interaction, as additional covariates. None of these predictors were significantly related to FeNO (ps N 0.202), and the other results reported above did not change. 4. Discussion Building on previous findings, this study sought to examine the relationship between psychosocial factors and FeNO in healthy individuals. Specifically, we were interested in associations between social support and FeNO, over and above previously demonstrated associations of FeNO with stress and negative affect variables. Changes in FeNO have been previously found to be associated with stress, depression, and negative affect (Ritz and Trueba, 2014). In this study, we built and expanded on these findings by also examining the role of social support in FeNO, a factor which has previously been found to be related to other inflammatory and immune biomarkers (Costanzo et al., 2005; Friedman et al., 2005; Lutgendorf et al., 2000; Lutgendorf et al., 2005) and cardiovascular physiology (Angerer et al., 2000; Kamarck et al., 1990). We also sought to study within-individual effects by the use of a longitudinal design with repeated measurements over a one-month time period. Of all the psychological factors examined in this study, social support was the only factor significantly related to FeNO. Overall, greater perceived social support was related to greater FeNO. When examining the three subscales of our social support measure (Family, Friends, and Significant Others), we found that none of these subscales was significantly related to FeNO over and above the others. The analysis separating the between- and within-individual effects showed that this overall relation was primarily due to the withinsubject effect across time because it was significant while the between-individuals effect was not. It is possible that FeNO differences between individuals may be primarily related to other factors that are not necessarily associated with social support, such as gender, age, or individual metabolic differences (Bucca et al., 2012). This pattern of results for social support may also be a function of the lower variance of the within-subject changes in NO versus differences in NO between individuals. Prior findings suggest that social support is associated with changes in a range of immune parameters in individuals that are healthy, as well as in those with a medical condition. Lower emotional support among HIV-infected men has been related to greater reductions in CD4 cell counts in subsequent years of a longitudinal study (Theorell et al., 1995). Spouses of individuals suffering from cancer that reported higher social support levels had stronger immune system reactions to challenges, as indicated by stronger natural killer cytotoxicity and greater proliferation responses to phytohemaglutinin (Baron et al., 1990). Another study found that high social support from friends was related to a stronger cellular immune response; Epstein Barr virus VCA antibody titers to a latent virus among highly educated women with breast cancer diagnoses or in the process of awaiting further diagnosis after an abnormal mammogram (Fagundes et al., 2012). In contrast, findings also suggest that lower social support is related to a reduced

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immune response to Hepatitis B vaccinations (Glaser et al., 1992), and loneliness, indicating a lack of social support, has a similar effect (Pressman et al., 2005). Taken together, these findings suggest that low social support and loneliness may make individuals more susceptible to infections. Indeed, Cohen et al. (1997) found that individuals with greater and diverse social networks were less likely to have a respiratory infection after being inoculated with a virus. Social support has also been found to be related to cardiovascular health. Low social support has also been associated with an increased risk of atherosclerosis (Angerer et al., 2000; Knox et al., 2000; Seeman and Syme, 1987) The effect of social support on biomarkers has also been previously examined as a moderator of stress, in which social support acts as a buffer to the negative effects of stress on biomarkers. Therefore we also tested social support as a potential moderator between psychological predictors such as: perceived stress, depression, negative affect and outcome: FeNO. We found that the association between psychological factors and FeNO was independent of social support. However, we did find a significant interaction between perceived stress and social support predicting FeNO. In particular, we found that social support was linked to higher FeNO only when our participants had low stress. Further, our results are consistent with previous studies which found that the association of stress and health-linked biomarkers is dependent on social support (Frasure-Smith et al., 2000), although we did not see a specific significant relation between stress and FeNO for participants with low social support. It is possible that we did not find a significant relationship between stress and FeNO at either high or low levels of social support because stress was measured at a single point. Thus, we were unable to ascertain the relation between fluctuations of stress and fluctuations in FeNO over time, which might have been a more sensitive test. The findings presented in our study may contribute to the previous research; they suggest that social support can have positive implications for health by its association with increasing NO production or release. The health implications of alterations in FeNO are difficult to ascertain, because FeNO is derived from several cell sources in different quantities which can lead to either beneficial or detrimental effects. We are not aware of studies that have determined the proportion of FeNO produced by each cell source. However, there is some evidence to suggest that the FeNO levels in individuals with chronic airway inflammation have a greater proportion of NO derived from iNOS (Roos et al., 2014), whereas in healthy individuals, FeNO is more a product of basal constitutive NO (Barnes and Kharitonov, 1996). cNOS activity produces basal NO in low quantities that can be temporarily upregulated with certain signals. This NO production is associated with beneficial effects on health. In contrast, proinflammatory signals can activate iNOS activity leading to a much higher expression of NO that is associated with detrimental and cytotoxic effects (Barnes, 1996; Esch et al., 2002). It could be that for individuals with abnormally elevated FeNO, further increases in NO would be detrimental to their health, while individuals with low or normal levels may benefit from an increase in NO. Independent of the source of the FeNO, overall research suggests that a reduction in FeNO can also have a range of adverse health consequences. NO production protects against infections from pathogens such as fungi, protozoa, and helminthes (MacMicking et al., 1997) and viruses (Vareille et al., 2011). In addition, NO has also been found to have bactericidal and bacteriostatic properties that aid in fighting bacterial infections (Chakravortty and Hensel, 2003). Reductions in NO expression in immune cells such as macrophages and epithelial cells in the presence of a pathogen can increase the risk of infection. NO can also induce natural killer cell activity and reduce auto-reactive T cell responses (Esch et al., 2002). NO expression is also closely related to cardiovascular health. NO expressed from endothelial cells can increase the blood supply to tissues, thus preventing ischemia (Bolli, 2001). It also protects against thrombosis by preventing the aggregation of platelets and their adherence to vascular walls (Bian et al., 2008). There is evidence that FeNO is inversely related to atherosclerosis

(Salonen et al., 2012) and that NO can reduce the likelihood of hypertension by altering basal vascular tone (Bian et al., 2008; Welch and Loscalzo, 1994). Reduced FeNO levels have been found in individuals with heart failure related to elevated vascular tone and pulmonary vascular tone (Sumino et al., 1998) and in patients with pulmonary arterial hypertension (Kaneko et al., 1998; Ozkan et al., 2001). In contrast to previous findings (Trueba et al., 2013), we did not observe that FeNO was related to depression, negative affect, anxiety, or perceived stress. One possible explanation for these null findings is the limited range of depressive symptoms during the course of the 5 weeks. In contrast to our previous findings on the association between depression and FeNO in the context of final exam stress, in this study we measured basal FeNO levels across several weeks in which there was relatively low challenge. This difference in methodology between the two studies may explain the diverging findings. The findings presented in this study should be interpreted while considering a number of limitations. First, FeNO measurements do not distinguish the exact source of NO production. NO values presented in this study could potentially reflect the expression of NO from endothelial, neural, or epithelial cells. Interpretations with respect to specific health implications need to be made with caution, as NO is related to a broad range of health outcomes. Second, the majority of the participants in our study were female students and healthy, which limits the generalizability of our findings to other populations. Third, although we excluded individuals with asthma and allergic rhinitis, we did not directly test for atopy in participants, making it possible that some of the participants were asymptomatic atopics. Atopy is related to elevated FeNO expression (Horváth and Barnes, 1999), thus allergy-induced FeNO elevations or possible exacerbations of undetected allergies may have occurred, affecting our study of between- and within-individual associations. Although confounds may be mostly unsystematic, they could have reduced our chance to demonstrate significant associations with psychological variables. Fourth, our sample size was small. These findings should therefore be replicated in studies with larger sample sizes. Replicating our findings in studies that examine the relationship between FeNO and social support in a laboratory setting where social support is manipulated would further strengthen our findings. Fifth, some participants missed some of their weekly appointments, resulting in 20% missing data. Although our MLM models include all participants regardless of missing data, we cannot definitively determine that the missing data did not impact our results. Finally, our study was naturalistic and correlational; therefore, these findings should be replicated using an experimental design. Overall, the findings of this study provide preliminary evidence that social support is associated with greater NO production or release in health. Although this study was not able to determine the health consequences of changes in FeNO due to increased social support, it is possible that these social support-induced increases in FeNO may be beneficial to immune, respiratory, and cardiovascular health. Future research should further examine the impact of social support on health as it relates to changes in FeNO. Studying the relationship between social support and FeNO may also be informative in populations suffering from chronic disease. Acknowledgments We thank Elizabeth Ebb for her help in collecting the data. References Abba, A.A., 2009. Exhaled nitric oxide in diagnosis and management of respiratory diseases. Ann. Thorac. Med. 4, 173–181. Aiken, L.S., West, S.G., 1991. Multiple Regression: Testing and Interpreting Interactions. Sage Publications Inc., Newbury Park, CA. Alving, K., Janson, C., Nordvall, L., 2006. Performance of a new hand-held device for exhaled nitric oxide measurement in adults and children. Respir. Res. 7, 1–17. American Thoracic Society, European Respiratory Society, 2005. ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled

A.F. Trueba et al. / International Journal of Psychophysiology 93 (2014) 356–362 lower respiratory nitric oxide and nasal nitric oxide. Am. J. Respir. Crit. Care Med. 171, 912–930. Angerer, P., Siebert, U., Kothny, W., Mühlbauer, D., Mudra, H., von Schacky, C., 2000. Impact of social support, cynical hostility, and anger expression on progression of coronary atherosclerosis. J. Am. Coll. Cardiol. 36, 1781–1788. Appleyard, K., Egeland, B., Sroufe, L.A., 2007. Direct social support for young high risk children: relations with behavioral and emotional outcomes across time. J. Abnorm. Child Psychol. 35, 443–457. Arnal, J.F., Dinh-Xuan, A.T., Pueyo, M., Darblade, B., Rami, J., 1999. Endothelium-derived nitric oxide and vascular physiology and pathology. Cell. Mol. Life Sci. 55, 1078–1087. Barnes, P.J., 1996. NO or no NO in asthma? Thorax 51, 218–220. Barnes, P.J., Kharitonov, S.A., 1996. Exhaled nitric oxide: a new lung function test. Thorax 51, 233–237. Baron, R.S., Cutrona, C.E., Hicklin, D., Russell, D.W., Lubaroff, D.M., 1990. Social support and immune function among spouses of cancer patients. J. Pers. Soc. Psychol. 59, 344–352. Belvisi, M.G., Stretton, C.D., Yacoub, M., Barnes, P.J., 1992. Nitric oxide is the endogenous neurotransmitter of bronchodilator nerves in humans. Eur. J. Pharm. 210, 221–222. Bian, K., Doursout, M.F., Murad, F., 2008. Vascular system: role of nitric oxide in cardiovascular diseases. J. Clin. Hypertens. 10, 304–310. Bogdan, C., 2001. Nitric oxide and the immune response. Nat. Immunol. 2, 907–916. Bolli, R., 2001. Cardioprotective function of inducible nitric oxide synthase and role of nitric oxide in myocardial ischemia and preconditioning: an overview of a decade of research. J. Mol. Cell. Cardiol. 33, 1897–1918. Bucca, C., Cicolin, A., Guida, G., Heffler, E., Brussino, L., Rolla, G., 2012. Exhaled nitric oxide FeNO in non-pulmonary diseases. J. Breath Res. 6, 27–104. Carpiano, R.M., 2007. Neighborhood social capital and adult health: an empirical test of a Bourdieu-based model. Health Place. 13, 639–655. Chakravortty, D., Hensel, M., 2003. Inducible nitric oxide synthase and control of intracellular bacterial pathogens. Microbes Infect. 5, 621–627. Chen, E., Strunk, R.C., Bacharier, L.B., Chan, M., Miller, G.E., 2010. Socioeconomic status associated with exhaled nitric oxide responses to acute stress in children with asthma. Brain Behav. Immun. 4, 444–450. Chrapko, W.E., Jurasz, P., Radomski, M.W., Lara, N., Archer, S.L., Le Mellédo, J., 2004. Decreased platelet nitric oxide synthase activity and plasma nitric oxide metabolites in major depressive disorder. Biol. Psychiatry 56, 129–134. Cohen, S., Kamarck, T., Mermelstein, R., 1983. A global measure of perceived stress. J. Health Soc. Behav. 24, 385–396. Cohen, S., Doyle, W.J., Skoner, D.P., Rabin, B.S., Gwaltney, J.M., 1997. Social ties and susceptibility to the common cold. JAMA 277, 1940–1944. Costanzo, E.S., Lutgendorf, S.K., Sood, A.K., Anderson, B., Sorosky, J., Lubaroff, D.M., 2005. Psychosocial factors and interleukin‐6 among women with advanced ovarian cancer. Cancer 104, 305–313. Eller, N.H., Netterstrom, B., Gyntelberg, F., Kristensen, T.S., Nielsen, F., Steptoe, A., Theorell, T., 2009. Work-related psychosocial factors and the development of ischemic heart disease: a systematic review. Cardiol. Rev. 17, 83–97. Esch, T., Stefano, G.B., Fricchione, G.L., Benson, H., 2002. Stress-related diseases — a potential role for nitric oxide. Med. Sci. Monit. 8, 103–118. Fagundes, C.P., Bennette, J.M., Alfano, C.M., Glaser, R., Povoski, S.P., Lipari, A.M., Agnese, D.M., Yee, L.D., Carson III, W.E., Farrar, W.B., Malarkey, W.B., Chen, M., KiecoltGlaser, J.K., 2012. Social support and socioeconomic status interact to predict Epstein–Barr virus latency in women awaiting diagnosis or newly diagnosed with breast cancer. Health Psychol. 31, 11–19. Frasure-Smith, N., Lespérance, F., Gravel, G., Masson, A., Juneau, M., Talajic, M., Bourassa, M.G., 2000. Social support, depression, and mortality during the first year after myocardial infarction. Circulation 101, 1919–1924. Friedman, E.M., Hayney, M.S., Love, G.D., Urry, H.L., Rosenkranz, M.A., Davidson, R.J., Singer, B.H., Ryff, C.D., 2005. Social relationships, sleep quality, and interleukin-6 in aging women. Proc. Natl. Acad. Sci. U. S. A. 102, 18757–18762. Glaser, R., Kiecolt-Glaser, J.K., Bonneau, R.H., Malarkey, W., Kennedy, S., Hughes, J., 1992. Stress-induced modulation of the immune response to recombinant hepatitis B vaccine. Psychosom. Med. 54, 22–29. Gratziou, C., Rovina, N., Lignos, M., Vogiatzis, I., Roussos, C., 2001. Exhaled nitric oxide in seasonal allergic rhinitis: influence of pollen season and therapy. Clin. Exp. Allergy 31, 409–416. Hare, J.M., Nguyen, G.C., Massaro, A.F., Drazen, J.M., Stevenson, L.W., Colucci, W.S., Fang, J. C., Johnson, W., Givertz, M.M., Lucas, C., 2002. Exhaled nitric oxide: a marker of pulmonary hemodynamics in heart failure. J. Am. Coll. Cardiol. 40, 1114–1119. Harkins, M.S., Fiato, K.L., Iwamoto, G.K., 2004. Exhaled nitric oxide predicts asthma exacerbation. J. Asthma 41, 471–476. Hedeker, D., Gibbons, R.D., 2006. Longitudinal Data Analysis. John Wiley & Sons Inc., Hoboken, NJ. Herbert, T.B., Cohen, S., 1993. Stress and immunity in humans: a meta-analytic review. Psychosom. Med. 55, 364–379. Höglund, C.O., Axén, J., Kemi, C., Jernelöv, S., Grunewald, J., Müller-Suur, C., Smith, Y., Grönneberg, R., Eklund, A., Stierna, P., Lekander, M., 2006. Changes in immune system regulation in response to examination stress in atopic and healthy individuals. Clin. Exp. Allergy 36, 982–992. Horváth, I., Barnes, P.J., 1999. Exhaled monoxides in asymptomatic atopic subjects. Clin. Exp. Allergy 29, 1276–1280. Kamarck, T.W., Manuck, S.B., Jennings, J.R., 1990. Social support reduces cardiovascular reactivity to psychological challenge: a laboratory model. Psychosom. Med. 52, 42–58. Kaneko, F.T., Arroliga, A.C., Dweik, R.A., Comhair, S.A., Laskowski, D., Oppendisano, R., Thomassen, J.M., Erzurum, S.C., 1998. Biochemical reaction products of nitric oxide as quantitative markers of primary pulmonary hypertension. Am. J. Respir. Crit. Care Med. 158, 917–923.

361

Knox, S.S., Adelman, A., Ellison, R.C., Arnett, D.K., Siegmund, K., Weidner, G., Province, M.A., 2000. Hostility, social support, and carotid artery atherosclerosis in the National Heart, Lung, and Blood Institute Family Heart Study. Am. J. Cardiol. 86, 1086–1089. Kullowatz, A., Rosenfield, D., Dahme, B., Magnussen, H., Kanniess, F., Ritz, T., 2008. Stress effects on lung function in asthma are mediated by changes in airway inflammation. Psychosom. Med. 70, 468–475. Le Mellédo, J.M., Mahil, N., Baker, G.B., 2004. Nitric oxide: a key player in the relation between cardiovascular disease and major depressive disorder? J. Psychiatry Neurosci. 29, 414–416. Lim, K.G., Mottram, C., 2008. The use of fraction of exhaled nitric oxide in pulmonary practice. Chest 133, 1232–1242. Lutgendorf, S.K., Anderson, B., Sorosky, J.I., Buller, R.E., Lubaroff, D.M., 2000. Interleukin-6 and use of social support in gynecologic cancer patients. Int. J. Behav. Med. 7, 127–142. Lutgendorf, S.K., Sood, A.K., Anderson, B., McGinn, S., Maiseri, H., Dao, M., Sorosky, J.I., Geest, K.D., Ritchie, J., Lubaroff, D.M., 2005. Social support, psychological distress, and natural killer cell activity in ovarian cancer. J. Clin. Oncol. 23, 7105–7113. MacMicking, J., Xie, Q., Nathan, C., 1997. Nitric oxide and macrophage function. Annu. Rev. Immunol. 15, 323–350. Ozkan, M., Dweik, R.A., Laskowski, D., Arroliga, A.C., Erzurum, S.C., 2001. High levels of nitric oxide in individuals with pulmonary hypertension receiving epoprostenol therapy. Lung 17, 233–243. Pacher, P., Beckman, J.S., Liaudet, L., 2007. Nitric oxide and peroxynitrite in health and disease. Physiol. Rev. 87, 315–424. Pisi, R., Aiello, M., Tzani, P., Marangio, E., Olivieri, D., Chetta, A., 2010. Measurement of fractional exhaled nitric oxide by a new portable device: comparison with the standard technique. J. Asthma 477, 805–809. Pratt, L.A., Ford, D.E., Crum, R.M., Armenian, H.K., Gallo, J.J., Eaton, W.W., 1996. Depression, psychotropic medication, and risk of myocardial infarction. Circulation 94, 3123–3129. Pressman, S.D., Cohen, S., Miller, G.E., Barkin, A., Rabin, B.S., Treanor, J.J., 2005. Loneliness, social network size, and immune response to influenza vaccination in college freshmen. Health Psychol. 24, 297–306. Ricciardolo, F.M., 2003. Multiple roles of nitric oxide in the airways. Thorax 58, 175–182. Ricciardolo, F.L., Geppetti, P., Mistretta, A., Nadel, J.A., Sapienza, M.A., Bellofiore, S., Maria, G.U.D., 1996. Randomised double-blind placebo-controlled study of the effect of inhibition of nitric oxide synthesis in bradykinin-induced asthma. Lancet 348, 374–377. Ricciardolo, F.L., Sterk, P.J., Gaston, B., Folkerts, G., 2004. Nitric oxide in health and disease of the respiratory system. Physiol. Rev. 84, 731–765. Ritz, T., Trueba, A.F., 2014. Airway nitric oxide and psychological processes in asthma and health: a review. Ann. Allergy Asthma Immunol. 112 (302–208). Ritz, T., Ayala, E.S., Trueba, A.F., Vance, C.D., Auchus, R.J., 2011. Acute stress-induced increases in exhaled nitric oxide in asthma and their association with endogenous cortisol. Am. J. Respir. Crit. Care Med. 183, 26–30. Roos, A.B.., Mori, M., Grönneberg, R., Österlund, C., Claesson, H.E., Wahlström, J., Nord, M., 2014. Elevated exhaled nitric oxide in allergen-provoked asthma is associated with airway epithelial iNOS. PLoS One 9, e90018. Salonen, I., Huttunen, K., Hirvonen, M.R., Dufva, J., Groundstroem, K., Dufva, H., Salonen, R.O., 2012. Exhaled nitric oxide and atherosclerosis. Eur. J. Clin. Investig. 42, 873–880. Seeman, T.E., Syme, S.L., 1987. Social networks and coronary artery disease: a comparison of the structure and function of social relations as predictors of disease. Psychosom. Med. 49, 341–354. Selley, M.L., 2004. Increased E-4-hydroxy-2-nonenal and asymmetric dimethylarginine concentrations and decreased nitric oxide concentrations in the plasma of patients with major depression. J. Affect. Disord. 80, 249–256. Sessa, W.C., 2005. Regulation of endothelial derived nitric oxide in health and disease. Mem. Inst. Oswaldo Cruz 100, 15–18. Srivastava, N., Barthwal, M.K., Dalal, P.K., Agarwal, A.K., Nag, D., Seth, P.K., Srimal, R.C., Dikshit, M., 2002. A study on nitric oxide, β-adrenergic receptors, and antioxidant status in the polymorphonuclear leukocytes from the patients of depression. J. Affect. Disord. 72, 45–52. Stefano, G.B., Esch, T., 2005. Integrative medical therapy: examination of meditation's therapeutic and global medicinal outcomes via nitric oxide review. Int. J. Mol. Med. 16, 621–630. Sumino, H., Sato, K., Sakamaki, T., Masuda, H., Nakamura, T., Kanda, T., Nagai, R., 1998. Decreased basal production of nitric oxide in patients with heart disease. Chest 113, 317–322. Theorell, T., Blomkvist, V., Jonsson, H., Schulman, S., Berntorp, E., Stigendal, L., 1995. Social support and the development of immune function in human immunodeficiency virus infection. Psychosom. Med. 57, 32–36. Thorsteinsson, E.B., James, J.E., 1999. A meta-analysis of the effects of experimental manipulations of social support during laboratory stress. Psychol. Health 14, 869–886. Trueba, A.F., Smith, N.B., Auchus, R.J., Ritz, T., 2013. Academic exam stress and depressive mood are associated with reductions in exhaled nitric oxide in healthy individuals. Biol. Psychol. 93, 206–212. Uchino, B.N., 2006. Social support and health: a review of physiological processes potentially underlying links to disease outcomes. J. Behav. Med. 29, 377–387. Vareille, M., Kieninger, E., Edwards, M.R., Regamey, N., 2011. The airway epithelium: soldier in the fight against respiratory viruses. Clin. Microbiol. Rev. 24, 210–229. Watson, D., Clark, L.A., Tellegen, A., 1988. Development and validation of brief measures of positive and negative affect: the PANAS scales. J. Pers. Soc. Psychol. 54, 1063–1070.

362

A.F. Trueba et al. / International Journal of Psychophysiology 93 (2014) 356–362

Welch, G., Loscalzo, J., 1994. Nitric oxide and the cardiovascular system. Card. Surg. 9, 361–371. Yang, K., Xie, G., Zhang, Z., Wang, C., Li, W., Zhou, W., Tang, Y., 2007. Levels of serum interleukin IL-6, IL-1β, tumour necrosis factor-α and leptin and their correlation in depression. Aust. N. Z. J. Psychiatr. 41, 266–273. Yates, D.H., Kharitonov, S.A., Thomas, P.S., Barnes, P.J., 1996. Endogenous nitric oxide is decreased in asthmatic patients by an inhibitor of inducible nitric oxide synthase. Am. J. Respir. Crit. Care Med. 154, 247–250.

Zigmond, A.S., Snaith, R.P., 1983. The hospital anxiety and depression scale. Acta Psychiatr. Scand. 67, 361–370. Zimet, G.D., Powell, S.S., Farley, G.K., Werkman, S., Berkoff, K.A., 1990. Psychometric characteristics of the Multidimensional Scale of Perceived Social Support. J. Pers. Assess. 55, 610–617.