Vitamin D deficiency during pregnancy is relatively common and may cause significant adverse health issues for both mother and child. Studied health issues associated with low vitamin D status during pregnancy include preeclampsia, gestational diabetes, post postpartum depression, and low birth weight.
Recent research reports that having given birth two or more times, giving birth to more than one child at a time (e.g. twins), and non-tanned skin are significant risk factors for vitamin D deficiency during pregnancy.
Dr Andersen and colleagues in Denmark recruited 1,108 pregnant women who took part in the prospective “Odense Child Cohort.” Participants completed a questionnaire reporting skin tone, country of birth, pregnancy height and weight, and sun exposure habits. The researchers received information about body mass index (BMI), smoking habits, and the number of pregnancies the woman has had from examination notes. Between the 8th and 16th week of gestation, blood samples were drawn to assess vitamin D status.
The researchers found that 27.8% of the participants were vitamin D insufficient, while 3.5% were deficient or severely deficient. However, it must be pointed out that the researchers considered vitamin D insufficiency as < 20 ng/ml and deficiency < 10 ng/ml. If the authors used a cutoff point of 30 ng/ml, 70% of participants would be considered insufficient.
The authors report:
“Adjusted predictors of vitamin D insufficiency were overweight and smoking, whereas having a self-reported ‘darker white’ skin compared to ‘pale white’ or ‘white’ and being nulliparous [first pregnancy] were protective. The association between darker self-reported skin tone to higher vitamin D levels in an almost exclusive Caucasian population is interpreted as a result of tanning (increased UVB-exposure) rather than race-dependent darker skin.”
Interestingly, the number of times a woman has given birth was inversely correlated with vitamin D levels, regardless of season. The researchers also found that increased maternal age was surprisingly associated with increased vitamin D levels, particularly during winter months.
A small percentage of participants in the study were of non-European origin (classified as having one parent born outside Europe). Not surprisingly, non-European origin was associated with an increased risk of vitamin D deficiency during the summer season, most-likely due to decreased vitamin D synthesis compared to women of European origin. The vitamin D levels of the two groups were not significantly different during winter months.
In regards to smoking, insufficiency among smokers was most prevalent during the winter, but not summer months, suggesting smokers had lower overall supplemental and/or dietary intake of vitamin D.
The present study does have numerous limitations including small sample size, lack of generalizability (participants are mainly of European descent), the use of self-reported data in regards to skin tone, and lack of information on supplementation and dietary vitamin D intake.
The researchers suggest that evaluation of current supplement guidelines is needed to decrease the risk of health problems as a result of D deficiency during pregnancy.