Results
A total of 396 respondents (99 % response rate) aged 18–40 years completed the questionnaire, skin test measurement using FSTCM and Mx 18, anthropometric measurement, and blood test for vitamin D. The mean ± SD age of the respondents was 28.06 ± 4.09 years. A total of 77.5 % were of Malay ethnicity, followed by 11.2 % Chinese, 8.8 % Indian and 2.5 % others (Table
1). A total of 358 (90.4 percent) of respondents had serum 25(OH)D < 50 nmol/L. The median concentration of serum 25(OH) D was 27.11 nmol/L with a minimum value of 7.50 nmol/L and a maximum value of 121.43 nmol/L. Meanwhile, 43.9 percent respondents had serum 25(OH)D < 25 nmol/L. Only five respondents (1.3 %) had enough vitamin D (serum ≥ 75 nmol/L) (Table
2).
Table 1
Socio-demographic, antenatal, skin characteristics and vitamin D intake of first trimester pregnant women (N = 396)
A) Socio-demographic factors |
Age (year) | | | 28.06 ± 4.09 (min = 18, max = 40) |
Ethnic groups | | | |
Malay | 307 | 77.5 | |
Chinese | 44 | 11.2 | |
Indian | 35 | 8.8 | |
Others | 10 | 2.5 | |
Educational status | | | |
Primary School | 16 | 4.0 | |
Secondary School | 149 | 37.6 | |
Tertiary School | 231 | 58.4 | |
Working Status | | | |
Working | 301 | 76.0 | |
Not working | 95 | 24.0 | |
Household members | | | 3 (2,4) (min = 2, max = 12) |
Household income per month | | | RM3500 (2800,5000) (min = RM900, max = RM20 000) |
B) Factors related to antenatal |
Week of pregnancy | | | 10 (8,12) (min = 4, max = 12) |
Gravidity | | | 2 (1,3) (min = 1, max = 9) |
Parity | | | 0 (0,1) (min = 0, max = 6) |
Smoking status | | | |
Yes | 3 | 0.8 | |
No | 393 | 99.2 | |
Last Child Birth | | | |
≤ 2 years | 124 | 61.1 | |
>2 years | 79 | 38.9 | |
Not applicable (first pregnancy) | 193 | | |
Still breastfeeding | | | |
Yes | 41 | 22.9 | |
No | 138 | 79.1 | |
Not applicable (no child) | 217 | | |
Body Mass Index (BMI) before pregnancy(kg/m2) | | | 22.69 (19.95, 26.36) (min = 14.29, max = 53.90) |
Weight at first antenatal visit (kg) | | | 57.70 (49.60,68.00) (min = 33.00, max = 148.70) |
C) Factors related to skin |
Fitzpatrick skin classification | | | |
Skin type I -II | 103 | 26.0 | |
Skin type III | 173 | 43.7 | |
Skin type IV-VI | 120 | 30.3 | |
Melanin Indices (using Mexameter 18) (0-999.000) | | | 302.17 (245.00, 302.17) (min = 133.33, max = 949.33) |
Sun protection score (0-8) | | | 5 (4,5) (min = 0, max = 7) |
The length of time exposed to sunlight (minutes per week) | | | 37.50 (0,150) (min = 0, max = 1680) |
D) Factors related to vitamin D intake |
Intake of vitamin D in food (IU/day) | | | 202.16 (124.94, 334.62) (min = 13.50, max = 1523.12) |
The number of respondents taking antenatal supplements | | | |
Taking supplements containing vitamin D | 44 | 11.1 | |
Taking supplements without vitamin D intake | 6 | 1.5 | |
Not taking supplement | 346 | 87.4 | |
Calcium and vitamin D supplement | | | |
No | 386 | 97.5 | |
Yes | 10 | 2.5 | |
Intake of vitamin D from food and supplements (IU/day) | | | 220.04 (137.88, 376.45) (min = 15.10, max = 1523.12) |
The level of vitamin D taken from food and supplements (IU/day) | | | |
<200 IU/day | 178 | 44.90 | |
≥200 IU/day | 218 | 55.10 | |
Table 2
Serum vitamin D (25(OH)D) concentrations among first trimester pregnant women (N = 396)
Serum concentration of 25 (OH)D nmol/L | | | 27.11 (19.87,36.99) (min = 7.50, max = 121.43) |
Serum concentration of 25 (OH) D nmol/L (categorized) | | | |
<25.00 nmol/L | 174 | 43.9 | |
25-49.99 nmol/L | 184 | 46.5 | |
50-74.99 nmol/L | 33 | 8.3 | |
≥75 nmol/L | 5 | 1.3 | |
Serum concentration of 25 (OH) D nmol/L (categorized) | | | |
<50 nmol/L | 358 | 90.4 | |
≥50 nmol/L | 38 | 9.6 | |
Table
3 shows the association between each independent variable with hypovitaminosis D. Age, ethnicity, education level, Fitzpatrick classification, melanin indices, sun protection score and intake of vitamin D from food have association with hypovitaminosis D (
p < 0.05). The crude OR (95%CI) for intake of vitamin D from food was 0.998 (0.997,0.999) with
p value 0.042. When the data was fixed into two decimal point, it was not significant. The selected independent variables (
p <0.25) were age, ethnicity, education level, household income per month, household number, weeks of pregnancy, number of children/parity, Fitzpatrick classification, melanin index, sun protection score, vitamin D intake from food (IU/day), vitamin D intake from food and supplement (IU/day), and the level of vitamin D in foods and supplements (IU/day). However, in order to prevent the occurrence of multicollinearity, melanin index, vitamin D intake from food and supplements, and the level of vitamin D in foods and supplements (IU/day) were not included in the multivariable analysis. The Fitzpatrick classification was chosen as the method for skin color measurement because it is simple and easy to measure. Meanwhile, only vitamin D intake from meals was selected as the p value was lower. Employment status, monthly household income, household number, gestational age, parity, last child birth, breastfeeding, pre-pregnancy BMI, weight at first antenatal visit and length of time exposed to sunlight were not significantly associated with hypovitaminosis D (Table
3).
Table 3
Combination of descriptive and simple logistic regression analysis to show the relationship between risk factors and hypovitaminosis D (N = 396)
Age(year)c
| 27.91 ± 3.95 | 29.47 ± 5.07 | 0.91 | (0.84, 0.99) | 0.026 |
Ethnic groupsc
| Malay | 296 (96.40) | 11 (3.60) | 22.42 | (9.63, 52.21) | <0.001 |
Chinese | 24 (54.50) | 20 (45.5) | 1.00 | |
Indian | 32 (91.40) | 3 (8.60) | 8.89 | (2.36, 33.40) | 0.001 |
Others | 6 (60.00) | 4 (40.00) | 1.25 | (0.31, 5.06) | 0.754 |
Education levelc
| Primary | 11 (68.80) | 5 (31.20) | 1.00 | |
Secondary | 136 (91.30) | 13 (8.70) | 4.75 | (1.43, 15.80) | 0.011 |
Tertiary | 211 (91.30) | 20 (8.70) | 4.80 | (1.52, 15.18) | 0.008 |
Working Status | Working | 275 (91.40) | 26 (8.60) | 1.00 | 0.252 |
Not working | 83 (87.40) | 12 (12.60) | 0.65 | (0.32, 1.35) |
Household income per monthc
| 3500 (2800,5000) | 3750 (2500,5250) | 1.00 | (1.00, 1.00) | 0.060 |
Household membersc
| 3 (2,4) | 3 (2,5) | 0.90 | (0.75, 1.07) | 0.225 |
Weeks of pregnancy at first antenatal visitc
| 10.0 (8.0,12.0) | 11.5 (8.0,12.0) | 0.89 | (0.77,1.02) | 0.100 |
Parityc
| 0 (0,1) | 1 (0,1) | 0.79 | (0.61, 1.03) | 0.083 |
Last child birth | ≤ 2 years | 111 (89.50) | 13 (10.50) | 0.86 | (0.43,1.75) | 0.686 |
>2 yearsa
| 247 (90.80) | 25 (9.20) | 1.00 | |
Breastfeeding | Yes | 36 (87.80) | 5 (12.20) | 0.74 | (0.27,2.01) | 0.552 |
Nob
| 322 (90.70) | 33 (9.30) | 1.00 | |
BMI before pregnant (kg/m2) | 22.76 (20.00,26.25) | 22.15 (19.75,26.58) | 1.02 | (0.96,1.09) | 0.499 |
Weight at first antenatal visit (kg) | 57.85 (49.30,68.54) | 57.03 (51.49,65.61) | 1.01 | (0.98,1.03) | 0.569 |
Fitzpatrick Classificationc
| Skin type I-II | 83 (80.60) | 20 (19.40) | 1.00 | |
Skin type III | 163 (94.20) | 10 (5.80) | 3.93 | (1.76,8.77) | 0.001 |
Skin type IV-VI | 112 (93.30) | 8 (6.70) | 3.37 | (1.42,8.03) | 0.006 |
Melanin Indices (using Mexameter) | (0-999.000) | 306.17 (254.17,373.67) | 242.83 (181.08, 354.00) | 1.01 | (1.00,1.01) | 0.006 |
Sun protection score | (0-8)c
| 5 (4,5) | 3.5 (1,5) | 1.77 | (1.42,2.21) | <0.001 |
Total of respondents exposed to sunlight (10 am-2 pm) | Yes | 201 (90.10) | 22 (9.90) | 1.00 | |
No | 157 (90.80) | 16 (9.20) | 1.07 | (0.55,2.11) | 0.836 |
The length of time exposed to sunlight (minutes in week) | 35 (0,150) | 55 (0,210) | 1.00 | (1.00,1.00) | 0.570 |
Intake of vitamin D from food (IU/day)c
| 197.51 (122.70,332.05) | 263.81 (142.90,460.55) | 1.00 | (1.00,1.00) | 0.042 |
Intake of vitamin D from food and supplements (IU/day) | 215.080 (132.93,361.98) | 302.135 (147.89,515.74) | 1.00 | (1.00,1.00) | 0.064 |
The level of vitamin D in foods and supplements (IU/day) | | | | |
<200 IU/day | 165 (92.70) | 13 (7.30) | 1.64 | (0.82,3.32) | 0.165 |
≥200 IU/day | 193 (88.50) | 25 (11.50) | 1.00 | |
During the multivariable analysis there was no multicollinearity or interaction between variables. Hosmer Lemeshow goodness-of-fit was not significant and no outliers. Receiver Operating Characteristics (ROC) area under the arches of this study was 0.866 with p <0.001 and can accurately predict 86 % cases. The final model is shown in Table
4. Interpretation of the final model is as follows; 1) Malay pregnant women in first trimester have a 34 times higher risk to have hypovitaminosis D compared to Chinese pregnant women, 2) Indian pregnant women in the first trimester have a 17 times higher risk of hypovitaminosis D compared to Chinese pregnant women, and 3) Pregnant women in the first trimester with a secondary or tertiary level of education have 12 times and 14 times higher risk respectively to have hypovitaminosis D compared to pregnant women with a primary level of education. The forecast model of having hypovitaminosis D among pregnant women in the first trimester was: logit (P) = ln [P/1-P] = -1.61 + [3.52*Malays] + [2.82* Indians] + [2.50*secondary school education] + [2.67*tertiary school education] (Table
4).
Table 4
Multiple logistic regression analysis to determine the predictors of hypovitaminosis D (serum 25(OH) D < 50 nmol/L)
Ethnic groups | | | | |
Chinese | | 1.00 | | |
Malay | 3.52 | 33.68 | (2.81,88.56) | <0.001 |
Indian | 2.82 | 16.86 | (3.78,75.20) | <0.001 |
Education level | | | | |
Primary | | 1.00 | | |
Secondary | 2.50 | 12.12 | (2.71, 54.16) | 0.001 |
Tertiary | 2.67 | 14.38 | (3.31, 62.45) | <0.001 |
Constant | −1.608 | 0.200 | | 0.032 |
Discussion
In this study, the prevalence of hypovitaminosis D among pregnant women with various ethnicities and skin colors was high. Hypovitaminosis D is expected to be high as previous studies related to vitamin D conducted in Malaysia among children and Malay women were also high. The prevalence of hypovitaminosis D (serum 25 (OH) D < 50 nmol/L) among children aged 7 to 12 years old in primary schools in Kuala Lumpur was 70.4 % [
3]. Whereas, for Malay women (222 respondents) with mean ± SD age 47.7 ± 4.6 years, their mean ± SD serum 25(OH) D was 36.2 ± 13.4 nmol/L [
19]. This high prevalence of hypovitaminosis D was due to age, abdominal obesity and metabolic syndrome affecting vitamin D levels. The mean ± SD serum 25(OH) D among Malay ethnic in our study was 27.4 ± 12.5 nmol/L with mean ± SD age 27.6 ± 3.9 years. The serum vitamin D level was low probably because our respondents were first trimester pregnant women who may have morning sickness and limited outdoor physical activity. Hamid et al. [
20] reported that the prevalence of hypovitaminosis D (25 (OH) D serum <50 nmol/L) among pregnant women in the second and third trimester was 60 and 37 % respectively. The prevalence declined due to a significant increase in the intake of multivitamins in the third trimester [
20]. This is in line with our study, where the prevalence of hypovitaminosis D (25 (OH) D serum <50 nmol/L) in the first trimester was high (90.4 %) and only 11.1 % took supplements containing vitamin D. Moreover, most of them had just started the supplements and the results may not have affected their vitamin D status yet.
Maghbooli et al. [
21] reported that the prevalence of vitamin D deficiency (serum 25(OH)D <25 nmol/L) among pregnant women in Tehran was 70.6 % and the prevalence of severe vitamin D deficiency (serum 25(OH)D <12.5 nmol/L) was 28.8 %. They classified the level of serum 25 (OH) D into four groups; below 12.5 nmol/L as severe, 12.5 to 24.9 nmol/L as moderate, 25 to 34.9 nmol/L as mild, and more than 34.9 nmol/L as normal [
21]. In comparison, our results showed a much lower prevalence of vitamin D deficiency with 43.9 % having serum 25(OH)D <25 nmol/L (Table
2). This may be due to the multiethnic nature of our respondents. Ethnic Chinese in this study had better vitamin D results compared to Malays and Indians which contribute to the decrease of the overall measure. The low vitamin D status in Tehran was probably due to wearing of full dress and veil among all women, regardless of race and religion.
Data related to the prevalence of hypovitaminosis D among pregnant women in Southeast Asia is limited. Hien et al. [
10] reported that among pregnant women and those of reproductive age (15–49 years old) in Vietnam, the prevalence of having serum 25(OH)D < 50 nmol/L and < 75 nmol/L was 7 and 48 % respectively. The prevalence of hypovitaminosis D (serum 25(OH)D < 50 nmol/L) was low because the respondents comprised of both pregnant and non pregnant women, from a mix of urban and rural district, with some working in the farming sector. These contrasted with our study where our samples were pregnant women who lived in an urban district, in which none of them were farmers.
Charatcharoenwitthaya et al. [
22] stated that among pregnant women in Thailand, serum 25(OH)D < 75 nmol/L in the first trimester was 83.3 %, 30.9 % in the second trimester and 27.4 % in the third trimester. There were no predictive factors for serum 25(OH)D < 75 nmol/L in the first trimester. In the second trimester, there were two factors that predict inadequate vitamin D, namely not taking antenatal vitamins (OR 4.28; 95 % CI: 1.33–13.75;
p < 0.05) and inadequate serum vitamin D levels in the first trimester (OR 5.10; 95 % CI: 1.93–13.47;
p < 0.01). Predictors of low vitamin D among the third trimester pregnant women were they did not take milk that has been fortified with vitamin D (OR 11:42; 95 % CI: 3.12–41.86), did not take antenatal vitamin supplements (OR 9.70; 95 % CI: 2.28–41.19) and had low vitamin D level in the first trimester (OR 10.58; 95 % CI: 2.89–38.80). Lack of vitamin D was not found in pregnant women who consumed antenatal vitamin supplements. However, 20 pregnant women who consumed antenatal vitamins with vitamin D at least 400 IU/day still had inadequate vitamin D levels in the third trimester [
22]. Charatcharoenwitthaya et al. [
22] suggested that vitamin D deficiency is common among pregnant women in Thailand, especially in the first trimester [
16]. Their study was similar to ours, where intake of vitamin D supplement or prenatal vitamins containing vitamin D in the first trimester was not associated with adequate serum 25(OH)D level. This was due to only 11.1 % respondents took vitamin D supplements or antenatal vitamin supplements containing vitamin D in the first trimester.
Pérez-López et al. [
23] stated that the prevalence of hypovitaminosis D (serum 25(OH)D <50 nmol/L) for pregnant women in Spain was 22.7 %. The study revealed that the factors associated with hypovitaminosis D were season of sampling, nulliparity, maternal weight and non-Caucasian ethnic groups [
23]. The prevalence of hypovitaminosis D (serum 25 (OH) D <50 nmol/L) in our study was four times higher than Spain. The difference may be due to factors such as sample size, methodology, study design, sampling season, as well as ethnic and genetic characteristics of the participants, and/or other factors which may affect the biological diversity of the results.
Our main problem is the variation in the definition of vitamin D deficiency. The laboratory measurement techniques for measuring vitamin D are also different. In order to standardize the level of vitamin D, cut off point for serum 25(OH) D of <50 nmol/L was used for comparison between various studies. This concentration has been used in other vitamin D studies in Malaysia [
1,
2,
24]. In fact, there are a few studies abroad that also used the term hypovitaminosis D as serum 25(OH)D <50 nmol/L [
25‐
27].
Chailurkit et al. [
28] stated that hypovitaminosis D was higher among adult in Thailand. Their research involved a Thai population aged 15 to 98 years with a sample size of 21 960. Their low serum 25(OH)D was associated with young urban women. Meanwhile, the mean ± SD serum 25(OH)D in their study was 73.0 ± 0.8 nmol/L [
28], which is far greater than the median (IQR) serum 25(OH)D in our study which is 27.11 (19.87, 36.99) nmol/L. This may be related to predictors used by Chailurkit et al. [
28] that were included in our study selection criteria. Our study was conducted in an urban district in the first trimester of pregnancy among mothers aged between 18 and 40 years. The significant predictive factors after multivariable analysis in our study were ethnic group, educational status and dietary intake of vitamin D. However, the study by Chailurkit et al. [
28] covered both urban and rural areas.
The majority of respondents in our study were Malay pregnant women (77.5 %) aged around 28 years old with a high level of education (58.4 %), working (76.0 %), with a household number of three and a total family income around RM3500. Ethnicity plays an important role and was one of the predictors for hypovitaminosis D in our study. Green et al. [
2] found that Chinese women in Kuala Lumpur had 14 nmol/L higher concentrations of serum 25 (OH) D with a lower prevalence of hypovitaminosis D compared to Indians and Malays. Rahman et al. [
29] also mentioned similar findings, where the level of serum 25(OH)D was significantly lower in postmenopausal Malay women (44.4 ± 10.6 nmol/L) compared to Chinese women (68.8 ± 15.7 nmol/L). In our study, first-trimester Malay and Indian pregnant women had 34 times and 17 times higher probability of hypovitaminosis D respectively compared to Chinese pregnant women. This finding may be related to sun protection factor and skin color. Majority of Malay respondents have skin color type III, Indian respondents have skin color type IV and Chinese respondents have skin color type II. Mean ± SD sun protection for Malay, Indian and Chinese respondents were 4.73 ± 0.76, 3.17 ± 1.20 and 2.02 ± 1.41 respectively (not in table). After the analysis of the data among Malay ethnicity, the risk factors for hypovitaminosis D were health education status (secondary education) and high sun protection score.
In term of education, 4 % of pregnant women only attended primary school education. This result was expected as the samples were recruited from urban areas. Leffelaar et al. [
30] claimed that in their study, among 4236 pregnant women in Amsterdam, there was a significant association between education level and serum 25 (OD) levels. They reported that women with low education have lower serum 25(OH)D compared to highly educated women (
p < 0.001). This result is also similar to the study by Van Den Berg et al. [
31], where in their cohort study of 2274 pregnant women in the Netherlands, serum 25(OH)D level in early pregnancy was significantly and positively associated with education level. Logistic regression analysis was carried out to show that women with lower education had lower serum 25(OH) D and higher risk of small for gestational age (SGA) fetuses (OR 1.95 [95 % CI; 1.20–3.14]). Holvik et al. [
32] also claimed that increased duration of education was associated with increased serum 25(OH)D among women. The association was not valid for men [
32]. Rock [
33] reported that a higher level of education, physical activity and a lower BMI were associated a higher intake of multivitamins-multiminerals.
Educational status was one of the significant predictors for hypovitaminosis D in our research, albeit with a negative association. Our findings showed that primary education predicted a higher serum 25(OH)D, in contradiction with previous studies. This is likely due to more exposure of respondents with lower education to sunlight in their daily activities as a result of poorer amenities such as lack of protective private transportation (e.g car) and holding a manual job with prolonged solar exposure. Sunscreen cream may be a luxury not available to this group of women during outdoor activities. However, this assumption would not be effective for countries with less exposure to the sun, where low education was associated with lower serum 25(OH)D, perhaps as a result of less dietary intake of vitamin D and less opportunity for sunbathing leisure and vacation. Hien et al. [
10] claimed that work status (farmer versus non farmer) have significant impact on vitamin D levels, where farmers had higher levels of serum 25(OH)D compared to non-farmers. However, their study did not mention the association between educational level and serum 25(OH) D.
Mithal et al. [
26] concluded from other studies in developing countries that economic status and high family income showed a lower prevalence of hypovitaminosis D in all age groups. High-income families provided better outdoor activities for school teenagers, better antenatal care facilities for pregnant women, consumed balanced diet and could afford vitamin D supplements for their older people. Most of the studies claimed that there was no association between household income per month and vitamin D status [
34]. This was similar to our study where household income was not associated with hypovitaminosis D. Our respondents were first trimester pregnant women, some of them were having morning sickness that causes poor dietary intake. They probably rarely spent their time outside home and avoided exposure to the sun. Their unstable condition prevented them from having a balanced diet and being active despite a high household income.
Our study reported that 51.3 % of respondents were pregnant more than once, 54.8 % had no children, 99.2 % did not smoke, 61.1 % had last child birth two years ago and below, median (IQR) BMI before pregnancy was 22.69 kg/m
2 (19.95, 26.36) and median (IQR) body weight in the first antenatal visit was 57.70 kg (49.60, 68.00). None of the antenatal history associated with vitamin D status. Charatcharoenwitthaya et al. [
22] also claimed that there was no significant relationship between pre-pregnancy BMI parity or gravidity with insufficient vitamin D level in any trimester. Clifton-Bligh et al. [
25] who conducted a study on 307 pregnant women in Australia also showed similar results where the weight (
p = 0.87) or BMI (
p = 0.35) was not associated with serum 25(OH)D levels.
However, several studies showed associations between BMI and serum 25 (OH) D. The higher the BMI, the lower the serum 25(OH)D [
1,
3,
13]. This was not found in our study as most of our respondents have normal weight, aged about 28 years and were in their first pregnancy. Wortsman et al. [
35] reported that BMI had a negative moderate correlation with serum 25(OH)D after irradiation (
r = -0.55,
p = 0.003). They also claimed that obesity was related with hypovitaminosis D [
35]. This may be due to a decreased ratio of body surface area to bulk with increased body weight and deposition of nutritional elements such as vitamin D in body fat.
Majority of our respondents had skin type III, median (IQR) melanin indices of 302.17 (245.00, 302.17), median sun protection score of 5 (4,5) and length of time exposed to sunlight (minutes per week) of 37.50 (0150) minutes. We have divided skin type into three classes, skin types I-II, skin type III and skin types IV-VI. This classification is based on the Fitzpatrick skin reactions when exposed to the sun. Skin type I-II is pale or fair, flammable and rarely turns dark/tan. Skin type III is flammable and turns dark, and is the commonest type in the United States. Skin types IV to VI, do not burn but easily turns dark [
18]. Many previous studies reported that skin color type was associated with serum 25(OH)D. Clemens et al. [
36] claimed that increased skin pigmentation can reduce the transmission of ultraviolet rays to synthesize vitamin D3 and this leads to a high risk of vitamin D deficiency. Armas et al. [
37] also stated the same opinion that any effect of ultraviolet (UV) on the level of serum 25 (OH) D depends on skin pigmentation and the amount of UV received. Our study showed similar results where fair skin such as Chinese had a higher level of serum 25(OH) D. Initially, by using simple logistic regression analysis, the skin color type, melanin index measurement and sun protection score showed correlation with vitamin D status (
p < 0.05). After using multivariable analysis (binary logistic regression), the final model showed that ethnicity is a predictor of serum 25(OH) D levels. Malay ethnicity was associated with high sun protection score, while Indian ethnicity was associated with high skin pigmentation. Clifton-Bligh et al. [
25] also reported that serum 25(OH) D was associated with ethnicity, whereby serum 25(OH) D levels were lower in women who originated from the Indian subcontinent and the Middle East.
Self-reported duration of time exposed to sunlight (minutes per week) in this study showed that respondents tend to spend more time indoors than outdoors between 10 am until 2 pm in the afternoon. Of 396 respondents, 223 (56.31 percent) were exposed to sunlight between 10 am and 2 pm. Although more than half of respondents were exposed to sunlight, most of them were exposed for only a short period of time with median (IQR) length of time exposed of 37.50 (0150) minutes in a week. In addition, most Malaysians avoid going out at that particular time of day because of the hot and sunny weather. Certain dress code and sun block had limited the ability of the skin to synthesize vitamin D.
Vitamin D intake from food is one of the modifiable factors that can reduce the risk of hypovitaminosis D. A total of 55.1 % of respondents have met the Malaysian Recommended Nutrient Intakes (RNI) for vitamin D in pregnant women which require intake of 5 μg (200 IU) per day [
38,
39] (Table
1). Although over half of respondents had met the RNI for vitamin D (≥200 IU/day), many respondents still had serum 25(OH)D < 50 nmol/L. The RNI is considered too low as many pregnant women had serum 25(OH)D < 50 nmol/L. Meanwhile, the Institute of Medicine [
40] reported that the Recommended Dietary Allowance (RDA) of vitamin D for pregnant mothers is 600 IU/day. Charatcharoenwitthaya et al. [
22] also claimed that there was a significant difference in serum 25(OH)D between pregnant women who took 400 IU or more vitamin D as supplements during the antenatal period and pregnant women who took < 400 IU/day or none (OR 0.19; 95 % CI: 0.06 to 0.56, p <0.01).
There are several limitations in this study, one of which was recall bias, as data was obtained through interview. In order to avoid such problems, a trained interviewer would often use different questions with the same meaning or repeat the questions several times. The other issue was the compliance to the antenatal vitamins prescription as there were no pill calculations. The confidence interval was relatively huge for ethnic groups. Although the overall sample size was sufficient, the sample size for Chinese and Indian were not adequate. Malaysian survey carried out in 2010 claimed that the Malays have high fertility rate of 2.8 children per woman, compared to 1.8 and 2.0 children among every Chinese and Indian woman respectively. The prevalence of hypovitaminosis D (serum < 50 nmol/L) may not be comparable to other populations as our respondents were first trimester pregnant women staying in town with no involvement in any agricultural activity.
Finally, awareness of high prevalence and dangers of hypovitaminosis D during pregnancy needs to be highlighted to health care workers so that they are better informed of factors influencing vitamin D status. Health care workers should also know the functions and the sources of vitamin D, so that advice could be given to patients especially those with lactose intolerance or low milk consumption during pregnancy. Calcium supplement with vitamin D should be given earlier to those who do not consume adequate milk during pregnancy to prevent adverse health effects to the mother and fetus.
Acknowledgements
The authors would like to thank the Director General of Health Malaysia for permission to publish this paper, all respondents, Mr Khairulnizan Abd Rani, and Dr Ahamad Jusoh and all health care staff in Petaling District Health Office who were directly or indirectly involved in this study. This work was supported by the Exploratory Research Grant Scheme from the Ministry of Education (ERGS/1/2013/SKK07/UKM/02/2) and the National University of Malaysia Fundamental Grant (FF-039-2013).