Smoking during pregnancy reduces vitamin D levels in a Finnish birth register cohort

Abstract

Objective Maternal vitamin D level in pregnancy may have implications for both the mother and fetus. Deficiency of vitamin D has been linked to several pregnancy complications and fetal skeletal health. Smoking has been associated with reduced serum level of the vitamin D metabolite, 25-hydroxyvitamin D (25(OH)D). Design A nested case-control study within the Finnish Maternity Cohort, a population-based cohort which includes first-trimester sera from 98 % of pregnancies in Finland since 1987. The selection consisted of women with uncomplicated pregnancies. We studied serum concentration of 25(OH)D in 313 non-smoking and forty-six self-reported smoking pregnant women. Setting We hypothesize that pregnant smokers may have an increased risk of low 25(OH)D levels especially during winter months. Participants A control group from an unpublished pregnancy complication study consisting of 359 uncomplicated pregnancies. Individuals who reported that they do not smoke were considered 'non-smokers' (n 313) and those who reported continued smoking after the first trimester of pregnancy were considered 'smokers' (n 46). Results Smokers had significantly lower levels of 25(OH)D irrespective of sampling time (P