European Journal of Clinical Nutrition (2002) 56, 51–56 ß 2002 Nature Publishing Group All rights reserved 0954–3007/02 $25.00 www.nature.com/ejcn
ORIGINAL COMMUNICATION Vitamin D deficiency: a concern in premenopausal Bangladeshi women of two socio-economic groups in rural and urban region MZ Islam1, C Lamberg-Allardt1*, M Ka¨rkka¨inen1, T Outila1, Q Salamatullah2 and AA Shamim2 1 Division of Nutrition, Department of Applied Chemistry and Microbiology, University of Helsinki, Finland; and 2Institute of Nutrition and Food Science, University of Dhaka, Dhaka, Bangladesh
Objective: The study was designed to evaluate the vitamin D status in women of different physiological status of two socioeconomic groups in Bangladesh. Design: A cross-sectional study, using serum 25-hydroxyvitamin D (25-OHD), calcium, phosphorus and alkaline phosphatase activity. Setting: Two regions of Bangladesh. The Dhaka city area and west region of Nandail (Betagair Union), Mymensingh. Subjects: Representative subjects of two groups (low socio-economic group ¼ group L, n ¼ 99; and high socio-economic group ¼ group H, n ¼ 90) of Bangladeshi women aged 16 – 40 y. About 87% of the subjects were housewives and the rest, 13%, were distributed among other different professions. Each group comprised of three sub-groups (non-pregnant nonlactating ¼ 1, pregnant ¼ 2, and lactating ¼ 3). Results: The influence of socio-economic status and physiological status on serum 25-OHD concentration (P ¼ 0.038, P ¼ 0.015, respectively), serum calcium concentration (P < 0.001, P < 0.001, respectively) and alkaline phosphatase activity (P < 0.001, P < 0.001, respectively) were observed. The distribution of serum 25-OHD concentration in both groups was shifted overall toward the lower limit of the normal range. Seventeen percent of women in group L and 12% of women in group H had serum 25-OHD concentration < 25 nmol=l. Hypovitaminosis D (serum 25-OHD concentration 37.5 nmol=l) was observed in 50% of subjects in group L and 38% of subjects in group H, respectively. The prevalence of hypovitaminosis was higher in lactating subjects of the groups L and H (63 and 46%, respectively) than in the other sub-groups in the same group. Conclusions: The results of the study suggested that women in Bangladesh were at risk of hypovitaminosis D and lactation was an additional risk factor in low income groups. The situation may increase the risk of bone loss. Sponsorship: The study was supported by the Academy of Finland, University of Helsinki and NorFa, Norway. European Journal of Clinical Nutrition (2002) 56, 51 – 56. DOI:10.1038=sj=ejcn=1601284 Keywords: Bangladesh; socio-economic groups; vitamin D deficiency; women
*Correspondence: C Lamberg-Allardt, Department of Applied Chemistry and Microbiology, Division of Nutrition, Calcium Research Unit, PO Box 27, 00014 University of Helsinki, Finland. E-mail:
[email protected] Guarantors: MZ Islam and C Lamberg-Allardt. Contributors: MZI and CL-A designed the study and are the guarantors for the integrity of the article as a whole. MZI was the principal investigator in the study. He managed the field study including data collection, blood sample collection and laboratory analyses. He prepared the first draft and final version of the manuscript as well as performing statistical analyses together with MK and CL-A. TO provided expertise in the assessment of vitamin D status. QS and AAS provided proper guidance with expertise during field work of this study. Received 20 February 2001; revised 30 May 2001; accepted 6 June 2001
Introduction The endogenous synthesis of vitamin D is influenced by several factors such as the extent of skin exposure to UV radiation, atmospheric pollution, geographical latitude and altitude, season, cloud cover of the sun, time of the day and skin pigmentation (Holmberg & Larsson, 1980; Hutchinson & Hall, 1984). Several studies have been carried out about vitamin D status in subjects of different age groups as well as in women of different physiological conditions of the Asian and Mediterranean immigrants in European countries as well as other developed countries of the world (Gibson et al, 1987; Meulmeester et al, 1990; Brunvand & Haug, 1993; Alfaham et al, 1995; Henriksen et al, 1995; Brunvand et al, 1998; Falch
Vitamin D deficiency MZ Islam et al
52 & Steihaug, 2000). All these studies observed that a higher prevalence of vitamin D deficiency is a problem among the Asian immigrants. Vitamin D is essential for the maintenance of calcium homeostasis and bone mineralisation. Extreme deficiency of vitamin D in adults causes osteomalacia (Gibson, 1990; Chapuy et al, 1992). As evidenced from many studies in Europe and other countries, vitamin D deficiency in pregnant women may have adverse effects on fetal growth, bone ossification, tooth enamel formation, and neonatal calcium homeostasis (Specker et al, 1992; Specker, 1994). A greater weight gain has been observed among Asian women in Britain supplemented with vitamin D during the third trimester of pregnancy (Brooke et al, 1980). Low breast-milk concentrations of vitamin D have been reported among vitamin D-deficient mothers but in non-pregnant non-lactating women the effect of vitamin D deficiency is not clear. Vitamin D deficiency is very likely to happen due to increasing demand at rapid growth in fetal life, infancy, early childhood and puberty, during pregnancy, lactation and in the elderly (Alfaham et al, 1995). Physiological factors, lifestyle and environmental characteristics may be the cause of vitamin D deficiency (Webb et al, 1990; Salamone et al, 1993). Serum 25-hydroxyvitamin D (25-OHD) is used as an index of vitamin D status (van den Berg, 1993). Serum 25OHD concentration is an important determinant of serum calcium concentration and parathyroid function (Zeghoud et al, 1997). Secondary hyperparathyroidism with diminished bone density has been reported in Asian vegetarians, during pregnancy and in the elderly (Lips et al, 1983; Okonofua et al, 1987; Fonseca et al, 1988). A high prevalence of sub-clinical vitamin D deficiency was reported in veiled Kuwaiti women (El-Sonbaty & A-Ghaffar, 1996). High incidences of osteoporotic fractures have been reported in Indian women above 40 y of age (Shatrugana et al, 1990). Vitamin D deficiency was reported in varying degrees in tropical an subtropical countries among children and women (Rab, 1976; Bhattacharyya, 1992; Atiq et al, 1998). In some areas of Bangladesh, a high prevalence of nutritional rickets was reported in children (Ministry of Health and Family Welfare, 1995). Up to this time no study has been carried out on vitamin D status of women in Bangladesh. As Bangladesh is a predominantly Muslim society the practice of purdah (a covered-up style of dress for Muslim women) is very common in women of different socio-economic classes. Women avoid sunshine exposure as they think it makes their skin colour black. These factors predispose to a reduction in endogenous
synthesis of vitamin D. In addition, inadequate dietary intake of vitamin D may result in low vitamin D status. The present study was designed to evaluate the vitamin D status in women with a covered-up style of dress (Shari) of different physiological conditions of high and low socioeconomic groups.
Subjects and methods Subjects The study was conducted in two regions of Bangladesh. Bangladesh lies within a tropical to subtropical monsoon 0 0 climate zone which extends from latitude 20 43 to 26 36 N 0 0 and longitude 88 3 to 92 40 E. The Dhaka city area and west Nandail (Betagair Union), Mymensingh, were selected for subjects in high and low socio-economic groups, respectively. A total of 189 women were included from the two socio-economic groups (low socio-economic groups ¼ group L, n ¼ 99; and high socio-economic group ¼ group H, n ¼ 90) aged 16 – 40 y. The subjects of this study were mainly housewives who were engaged in household activities only (Table 1). They used a covered-up style dress called Shari but their faces and hands were uncovered. Depending on physiological conditions of the subjects each group consisted of three sub-groups (non-pregnant non-lactating ¼ 1, pregnant ¼ 2 and lactating ¼ 3). The socio-economic status was based on family income level. Group L consisted of rural women of precarious income levels, dependent on agricultural labour. The selected area for the subjects of low socio-economic group is located by the River Kachamatia, a tributary of Brahmaputra. It is a flood-prone zone of the country which is also affected by drought during the dry season. The women in group H were selected from affluent families of high income and education level from two locations (Malibag Chowdhurypara and Nakhalpara) in a newly developed part of Dhaka city. The pregnant subjects of the present study were at late first trimester to beginning of second trimester of their pregnancy and lactating subjects were within 2 y of lactation. None of the subjects used any Table 1
Distribution of the subjects in different professions
Socioprofessional classes
Group L
Group H
Percentage of the total subjects
88 4 1 5 1
76 14 — — —
86.8 9.5 0.5 2.6 0.5
Housewife Service Farmer Daily labourer Unemployed
Table 2 Basic characteristics of the study subjects (x s.d.) Sub-groups
L1
H1
P-values
L2
H2
P-values
L3
H3
P-values
Age (y) Weight (kg) Height (cm) 2 BMI (kg=m )
28.0 5.0 37.9 4.3 148.9 4.5 17.1 1.5
29.0 6.0 55.0 8.8 155.3 5.2 22.9 3.7
0.468 0.000 0.000 0.000
23.0 5.0 43.9 5.8 150.5 5.4 19.4 2.6
26.0 4.0 54.4 8.4 153.9 6.2 22.9 3.0
0.022 0.000 0.027 0.000
23.0 4.0 37.8 4.2 148.6 4.2 17.1 1.6
26.0 5.0 51.5 8.2 153.8 5.0 21.8 3.2
0.023 0.000 0.000 0.000
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Vitamin D deficiency MZ Islam et al
53 vitamin D supplementation. Time spent outside by the subjects was not collected. The descriptive data about the characteristics of subjects in two groups are summarised in Table 2. The study was approved by the ethical committee of the Faculty of Agriculture and Forestry, University of Helsinki. During field study in Bangladesh the ethical guidelines of the University of Dhaka were also followed.
between the sub-groups of two socio-economic groups with similar physiological status were carried out with two-sided t test using Bonferroni correction (Munro, 1993). Results are expressed as means s.d. The Mann – Whitney U-test was used for skewed distribution of variables. Taking Bonferroni correction into account the significance level P < 0.0167 was used (when three sub-groups were compared). The Pearson correlation coefficient was used to estimate the relationship between different biochemical variables. The analyses were carried out with Stata Statistical Software (1997).
Methods A blood sample was collected after overnight fasting from the subjects by disposable syringe through venepuncture and protected from sunlight. After clotting, serum was separated by complete centrifuge of blood sample. The serum was collected in tubes and preserved at 7 20 C. Finally, the serum sample was transported to Helsinki on dry ice in a special type of container and preserved in the freezing room of the Division of Nutrition, Department of Applied Chemistry and Microbiology, University of Helsinki for further analysis. Serum 25-OHD was used to evaluate the vitamin D status. The serum 25-OHD concentration was determined by radioimmunoassay method with kits from Nichols Institute (San Juan Capistrano, California, USA). The inter and intra-assay CVs were 14 and 15%, respectively. We defined vitamin D deficiency as serum 25-OHD levels < 25 nmol=l and the reference range was 25 – 120 nmol=l for adults. The serum levels of alkaline phosphatase activity, calcium and phosphate concentration were measured using an Elan Auto Analyzer with spectrophotometrical methods to get additional information about the vitamin D status. The CV for serum alkaline phosphatase activity, serum calcium and serum phosphate were 4.0, 1.4 and 2.9%, respectively. The food composition database used in this study does not contain vitamin D, so estimation of dietary vitamin D intake was not possible. The study was conducted during February to March and April to May in 1995 for low-income and high-income women, respectively. There is no difference in sunshine during this period that could substantially affect vitamin D status (Lamberg-Allardt, 1984).
Results Serum 25-hydroxyvitamin D concentration The nutritional vitamin D status is reflected by the serum 25OHD concentration. The influence of socio-economic status and physiological status on serum 25-OHD concentration (P ¼ 0.038, P ¼ 0.015, respectively) was observed. The serum concentration of 25-OHD was not significantly different between sub-groups L1 and H1 (P ¼ 0.906); L2 and H2 (P ¼ 0.385), whereas sub-group L3 had significantly lower levels of serum 25-OHD concentration compared with subgroup H3 (P ¼ 0.018; Table 3). In this study, no subject had serum 25-OHD level above the normal range (25 – 120 nmol=l) and the whole distribution in both groups was shifted toward the lower limit of the normal range. The observed median value of serum 25-OHD was 36.7 nmol=l in group L. The median value of serum 25-OHD was slightly higher (43.5 nmol=l) in group H (Figure 1). Vitamin D deficiency (serum 25-OHD levels < 25 nmol=l) was detected in 17% of women in group L (majority of them distributed in sub-group L3; ie 32%) and 12% in group H, respectively. Serum 25-OHD concentrations of 37.5 nmol=l resulting in increase of serum parathyroid hormone concentrations, corresponding to hypovitaminosis D (Thomas et al, 1998), were detected in 50% of group L subjects (the prevalence was much higher in sub-group L3 63%) and 38% of group H subjects, respectively.
Other variables Serum alkaline phosphatase activity normally reflects bone turnover and is usually high in vitamin D deficiency. The influence of socio-economic status and physiological status on serum alkaline phosphatase activity (P < 0.001, P < 0.001,
Statistical analyses The statistical analysis was carried out using a w2 test and two-way analysis of variance (ANOVA). Post-hoc analyses Table 3
Serum 25-OHD (nmol=l) concentrations in sub-groups of the two socio-economic groups Group L
Sub-groups L1 L2 L3
Group H
Serum 25-OHD
s.d.
Sub-groups
Serum 25-OHD
s.d.
P-value
39.9 44.8 32.6
12.5 20.0 16.1
H1 H2 H3
40.7 49.0 44.2
10.6 16.7 19.6
NS NS 0.01
NS not significant. Comparison between corresponding sub-groups. P-value calculated by a two-sided t-test after two-way analysis of variance.
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Vitamin D deficiency MZ Islam et al
54 difference was not statistically significant between subgroups L2 and H2 (2.41 0.22 vs 2.33 0.12 mmol=l, respectively; P ¼ 0.096). The serum calcium values were corrected for serum albumin but the results were similar (L1 vs H1, P ¼ 0.008; L2 vs H2, P ¼ 0.026; L3 vs H3, P ¼ < 0.001). The serum phosphate concentration showed a significant difference between sub-group L2 and H2 (1.41 0.18 vs 1.59 0.19 mmol=l, respectively; P ¼ 0.003), but there were no differences between the other two sub-groups of the two socio-economic groups (L1 vs H1, P ¼ 0.237; L3 vs H3, P ¼ 0.346, respectively). None of the subjects took pharmaceutical preparations of vitamin D. In the present study we found no significant correlation between serum alkaline phosphatase and 25OHD in subjects from high income groups, whereas a significant correlation was observed in the low income group (r ¼ 0.25, P < 0.05). Figure 1 Box plot presentation of the distribution of serum 25-OHD in the two socio-economic groups by sub-groups categories.
respectively) was also observed. Serum levels of alkaline phosphatase were significantly higher in sub-groups L2 and L3 of group L compared with their corresponding sub-groups in group H (L2 vs H2, P ¼ 0.047; L3 vs H3, P ¼ 0.002), but the difference was not statistically significant between subgroups L1 and H1 (P ¼ 0.057, Figure 2). None of the subjects in group H had serum alkaline phosphate activity above the reference limit ( > 350 U=l). Two subjects in sub-group L2 of group L had markedly high alkaline phosphates activity (360 and 376 U=l) with normal serum 25-OHD level (47.5 and 67 nmol=l). The serum calcium concentration was significantly lower in sub-group L1 than in sub-group H1 (2.41 0.29 vs 2.61 0.17 mmol=l, respectively; P ¼ 0.002) and in subgroup L3 than in sub-group H3 (2.17 0.22 vs 2.53 0.21 mmol=l, respectively; P ¼ < 0.001), whereas the
Figure 2 Serum alkaline phosphatase concentration in sub-groups of the two groups (bars showing the standard deviation).
European Journal of Clinical Nutrition
Discussion The result of the present study showed suboptimal vitamin D status among adult and premenopausal Bangladeshi women of both high and low socio-economic groups and a relatively higher prevalence of low serum 25-OHD concentrations (below 25 nmol=l) in lactating women of low socio-economic status. The observed mean serum 25-OHD levels among the subjects of this study were in general lower than those reported in US white women (Jacques et al, 1997) but similar to those of European women (Henriksen et al, 1995; Burnand et al, 1992; Lamberg-Allardt et al, 1993). Interestingly, the mean serum concentration of 25-OHD was higher in our subjects compared with the Asian women living in Europe and North America (Gibson et al, 1987; Alfaham et al, 1995; Henriksen et al, 1995) but much lower than healthy women in Thailand (Chailurkit et al, 1996). Vitamin D deficiency as well as higher prevalence of hypovitaminosis D (serum 25-OHD concentrations of 37.5 nmol=l) was observed in the study groups (Thomas et al, 1998). Among the possible explanations of this inadequate vitamin D status in Bangladeshi women of high and low socio-economic status as well as the non-significant difference in serum 25-OHD in the two groups could be avoidance of direct sunshine exposure due to house-bound lifestyle and misconceptions, traditional purdah system or excess clothing. The majority of the subjects in this study were dark-skinned women, and increased skin pigment affects the synthesis of cholecalciferol (Matsuoka et al, 1991). The mean concentrations of serum 25-OHD in pregnant women in the groups of both high and low socioeconomic status was higher compared with other subgroups in the same group but also closer to the vitamin D insufficiency level. Vitamin D deficiency was found in lactating women (sub-groups L3 and H3) in both groups compared with the other sub-groups in same group (the prevalence rate was 63 and 46%, respectively). This finding is consistent with earlier observations that the serum 25-OHD concentration
Vitamin D deficiency MZ Islam et al
55 decreases during the last trimester of pregnancy, which could be reflected in the lactating period (Kokkonen et al, 1982; Lamberg-Allardt et al, 1984). Fish and fish products, fortified margarine and milk are the major sources of vitamin D in many countries. As the locations were in non-coastal regions of Bangladesh, we found that fish consumption was low in both groups and there was no food fortified with vitamin D available at the time the study was performed. Therefore, nutritional vitamin D intake was probably low. An inadequate calcium intake mainly based on cereal sources was observed in the study groups (Islam et al, 2001). The cereal-based diet is known to have high content of phytic acids that inhibit calcium absorption, which may have an unfavourable effect on vitamin D status and bone metabolism (Clements et al, ¨ rkhem, 1988). Calcium 1987; Lawson et al, 1987; Berlin & Bjo deficiency increases the catabolism of 25-OHD in the liver and thereby increases the requirement of vitamin D (Clements et al, 1987). In human beings, exposure to sunlight ultraviolet B (UVB) radiation (290 – 315 nm) is the most important source for photosynthesis of vitamin D in the skin (Olveri et al, 1994). The seasonal variations in UVB radiation and its effect on skin synthesis of vitamin D among the subjects from the Northern Hemisphere have been observed in several studies (Kuoppala et al, 1986; Webb et al, 1988; Lamberg-Allardt et al, 1993; Scharla et al, 1996; Liu et al, 1997) but in a sunny country (Chile) there was no significant difference in serum 25-OHD between seasons (Aguirre et al, 1996). However, the information regarding seasonal variation in serum vitamin D and vitamin D status of different population groups in Bangladesh is scarce. A decrease in the vitamin D status with advancing age has been observed in several studies in different populations (Tsai et al, 1987; 1991; Dubbelman et al, 1993; van der Wielen et al, 1995). Therefore, the findings of this study suggest that elderly individuals in Bangladesh could be at substantial risk of inadequate vitamin D status and further study is recommended to detect the severity of vitamin D deficiency in this population group. The higher level of total alkaline phosphatase (ALP) activity in low income pregnant and lactating subjects (subgroups L2 and L3, respectively) indicated that bone turnover was increased in these sub-groups. Total ALP activity has its limitations as it reflects not only bone ALP activity but also liver and placental ALP activity. However, the higher level of serum ALP activity in low-income lactating women probably reflected bone isoenzymes, because there was a higher prevalence of lower values of serum 25-OHD in this sub-group. All subjects of this study were healthy and reported no diseases known to increase the liver ALP isoenzyme. In conclusion, the results of this study suggest that vitamin D deficiency and borderline vitamin D status are common in adult Bangladeshi women of different physiological statuses. The study indicated that both privileged, better-educated high-income women of an urban environment and the low-income women of a rural environment
were at risk of developing vitamin D deficiency. The prevalence of hypovitaminosis D status was much higher in low-income lactating women than any of the other subgroups of this study. Apparently, the main reasons for this situation are linked to traditional avoidance of sun exposure or lack of direct exposure to sunshine, diet failing to provide an adequate amount of vitamin D, and no use of supplementation. However, there is no reason to believe that these findings are not representative of other Bangladeshi women. Therefore, it is important to pay attention to this rather high prevalence of insufficient or borderline vitamin D status and more active measures need to be taken by giving information to health professionals and the subjects themselves about the importance of vitamin D for health, including the need for out-of-doors exposure to sunlight, adequate dietary intake of vitamin D and implementation of current recommendations to improve their vitamin D status. Further investigation is required to determine the potential benefits of intervention.
Acknowledgements The authors are grateful to Marika Hollme´ n, laboratory assistant, Division of Nutrition, University of Helsinki, for excellent technical assistance. The authors also express their sincere appreciation to the field workers, nurses and participants of this study. The study was funded by the Academy of Finland, University of Helsinki and NorFa, Norway.
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