A meta-analysis, published in the journal Advanced Biomedical Research,  which incorporated data from 14 clinical trials concluded that vitamin D plays a crucial role in the mental health of women during and after pregnancy.
 
According to most estimates, postpartum depression (PPD) is experienced by as many at 50-75% of new mothers following delivery, making mental health a significant issue women face. In total, nine of the studies reported that PPD and sleep disorders were significantly and/or directly associated with vitamin D intake. Beyond this, one study reported an indirect association, one study reported a direct association to anxiety but not to PPD, and three studies did not achieve any significant relationship between vitamin D status, sleep disorders, and PPD.
 
“A large amount of research explained adverse effects of PPD on the cognitive and emotional development of infants,” the authors wrote. “While they need sufficient sleep for their energy requirements, hormonal changes may cause energy loss and alter sleep quality, sleep duration, and eating habits in the early weeks of the post partum period.”
 
While the authors could not establish cause in this study, some research has theorized that vitamin D’s functions play a role as a hormone needed for normal brain homeostasis and development. “In the brain, it promotes neurotransmission, neurogenesis, synaptogenesis, amyloid clearance, and the prevention of neuronal death,” the authors said. “The active form of vitamin D is associated with production of serotonin by activating synthesis of tryptophan hydroxylase in the brain and also has protective effects against low levels of dopamine and serotonin. Insufficient levels of vitamin D are associated with several mental disorders such as anxiety, and sleep disorders such as restless leg syndrome (RLS) in pregnant women.”
 
One study, conducted on 796 pregnant women in Australia, measured serum vitamin D concentration at 18 weeks’ gestation, with PPD assessed three days after delivery with an abbreviated form of the Edinburgh Postnatal Depression Scale (EPDS), and it was shown that vitamin D had a protective effect against PPD with an odds ratio of 2.19.
 
In another Australia-based study, investigators analyzed 1040 cord blood samples to evaluate vitamin D level in pregnant women. PPD was then assessed 6 weeks and 6 months after delivery using EPDS – while the main objective of the study was to investigate the impact of omega-3 supplementation on pregnant women, a secondary outcome was that vitamin D did not have a significant association with PPD. However, cord blood has a lower level of vitamin D than maternal blood samples, suggesting that the use of cord blood was a limitation, in addition to the fact that vitamin D analysis was considered a secondary aim of the study.
 
Another study focused on the association between vitamin D, inflammation, and PPD, and found that vitamin D had a marginally significant inverse association with PPD, and that the observed association was mediated by the pro-inflammatory compound interleukin-6.
 
Oddly enough, a case control study found that serum vitamin D actually caused a greater risk of PPD, though the study recommended that vitamin D binding protein concentrations should be assessed, because they play a key role in the bioavailability of vitamin D.
 
In a Japanese study assessing 1319 pregnant women for dietary intake of dairy product by diet history questionnaire, researchers aimed to assess whether higher intakes of dairy products, calcium, and vitamin D during pregnancy could decrease the risk of PPD. They administered the EPDS questionnaire to the participants 3-4 months after delivery, and found no association with PPD risk, however, the lengthy follow-up on the questionnaire was considered a limitation in the study.
 
In another study, 179 pregnant women were examined at gestational weeks 24 and 28, with blood samples collected mid-pregnancy. Women completed the EPDS at 1 week, 6 weeks, and 6 months after delivery, and the study reported that women with PPD symptoms were more likely to have low levels of vitamin D.
 
A cohort study performed in South Carolina evaluated the results of 97 postpartum women, and found that low levels of vitamin D were an effective factor for developing PPD, though there were several confounding factors which were not controlled in the study, the authors said.
 
In another cohort study measuring serum vitamin D level at delivery and PPD in a 3 month survey follow-up of 218 women, the study reported that PPD as measured by the EPDS was most prevalent in women with a low level of vitamin D (less than 10.2 ng/ml) with an adjusted odds ratio of 0.81.
 
In a randomized, placebo-controlled clinical trial measuring outcomes in 81 Iranian women, patients were randomly assigned into three groups to receive either 50,000 IU vitamin D3 every two weeks and 500 mg of calcium daily, a biweekly dose of 50,000 IU vitamin D with a calcium placebo, or a placebo of both nutrients for 8 weeks. At baseline and at the end of the study, vitamin D3 and calcium had significantly lower instances of PPD than vitamin D supplementation alone, or full placebo supplementation.
 
In a study on American women at high risk of depression, which examined the effects of omega-3 supplementation on depressive symptoms, a secondary result showed that low level of vitamin D in early pregnancy was associated with depressive and anxiety symptoms during pregnancy, but not PPD.
 
In a cross-sectional study examining 498 pregnant women at 15.4 weeks on average, a series of depression, anxiety, and stress questionnaires were used to determine the association between serum levels of vitamin D and mental health symptoms, and the study reported an inverse association between anxiety symptoms and vitamin D concentration, especially in patients who did not report physical activity.
 
Another cross-sectional study evaluating low levels of serum vitamin D and associations with sleep disturbance didn’t find any correlation between sleep quality and low levels of vitamin D in an observational study of 92 pregnant women in their third trimester.
 
In a cohort study of 890 pregnant women at 26-28 weeks’ gestation in Singapore, the Pittsburgh Sleep Quality Index was used to measure potential sleeping disturbances, with dietary recall used in addition to vitamin D concentration measurements in plasma, and it was found that vitamin D deficiency had a causal relationship to poor sleep quality and night-time eating.