Pre- and Postnatal Vitamin D Beneﬁts
One of the primary roles of vitamin D is the regulation of calcium and phosphorus absorption and metabolism for bone health. This role is especially important during pregnancy and lactation because bones develop rapidly during this period. Women have less skin pigmentation than men, a ﬁnding attributed to women's greater need for vitamin D during pregnancy and lactation.27 Insufﬁcient vitamin D intake during infancy can result in biochemical disturbances, reduced bone mineralization, slower growth, bone deformities, and increased risk of fracture – the hallmarks of rickets.28 Indeed, rickets has been reported among breast-fed African-American infants in several southern states.29,30
The relationship between maternal vitamin D/calcium and fetal bone development was reviewed by Specker.31 Most of the papers reviewed reported an effect of maternal vitamin D status on both maternal and infant calcium homeostasis, but did not report whether infant bone mineral density (BMD) was affected.
Low birth weight (LBW) appears to be a consequence of vitamin D insufﬁciency during pregnancy. The topic was reviewed by Fuller, who hypothesized that insufﬁcient serum 25(OH)D levels disrupted calcium homeostasis, leading to intrauterine growth retardation, premature labor, and hypertension, all of which are risk factors for LBW infants.32 Subsequent papers seem to support the hypothesis that African-American and Asian-Indian mothers have much higher rates of LBW infants in the United States than do European Americans or Hispanic Americans.33-35 This may be in part because Hispanic Americans have a slightly higher consumption of vitamin D than African Americans,36 as well as lighter skin. Also, Koreans born in winter tend to have lower BMD than those born in summer.37
Children born prematurely are likely to have enamel defects in both primary and permanent teeth.38 Maternal vitamin D sufﬁciency is required for proper fetal tooth development,31,39 as well as adequate calcium. An additional beneﬁt of sufﬁcient vitamin D and calcium during pregnancy is good maternal bone health. Studies report 2-4 percent bone density losses during pregnancy that are exacerbated by calcium and vitamin D deﬁciency.31
Maternal and infant 25(OH)D sufﬁciency also appears to greatly reduce the risk of type 1 diabetes mellitus (DM). A study of vitamin D supplementation during the ﬁrst year of life found those receiving the highest amounts in Finland had an odds ratio of 0.2 of developing type 1 DM compared with those receiving no supplements.7,40 In further support of this hypothesis, mechanisms were investigated in a mouse model,41 and vitamin D receptor (VDR) alleles have been associated with risk of type 1 DM.42 The VDR bind 1,25-dihydroxy vitamin D3 (1,25(OH)2D) to its target cells and organs where it performs certain functions. The fact that VDR alleles are associated with a particular disease gives further support to vitamin D having an effect. In addition, there is an excess summer birth rate for those who develop type 1 DM.43 The most likely explanation is that maternal vitamin D insufﬁciency occurs during the second trimester of pregnancy, a time when the pancreas is likely to develop. Risk of type 1 DM related to vitamin D status should be considered when revising vitamin D guidelines.44
Maternal and infant 25(OH)D sufﬁciency is also linked to signiﬁcant reduction of risk for multiple sclerosis (MS). Vitamin D is hypothesized to reduce the risk of MS by strengthening the immune system against viral infections, a theoretical etiological factor in MS.45-47 Adequate serum 25(OH)D levels during pregnancy appear to reduce the risk of MS, as evidenced by seasonal variations in birth rate for those who later develop MS, with spring being the season of greatest birth rate for MS.48,49 A recent paper suggests vitamin D supplementation during pregnancy as a way to reduce the risk of fetal inclination toward MS.50
A study in England found birth seasonality was related to later diagnosis of bipolar disorder,51 strongly suggesting that the risk of bipolar disorder can be reduced through sufﬁcient vitamin D intake during pregnancy. The same can be said of anxiety neurosis, for which there is a very pronounced springtime excess birth rate; for example, in New South Wales.52 It is likely several other mental disorders and birth defects associated with springtime excess birth rates will be linked to maternal vitamin D deﬁciency earlier in pregnancy.