Physiological functions for vitamin D have been hypothesised based on the presence of the vitamin D receptors on the cells of interest. One such group of cells are neurones and glial within the central nervous system which have been shown to possess the vitamin D receptor. Brain regions that possess the vitamin D receptor also possess the ability to metabolise 25-hydroxyvitamin D to 1,25-hydroxyvitamin D, the active form of the hormone. This suggests that the central nervous system is affected by the presence of circulating vitamin D. The function of vitamin D in the central nervous system is not fully understood, but epidemiological research suggests an inverse association between depression and vitamin D. Sun exposure is required for skin production from vitamin D, and sun exposure is also known to relieve mild depression. Therefore vitamin D could be beneficial in cases of depression.
Research investigating the association between vitamin D and depression have produced some positive result. For example, researchers1 have used a cross-sectional and prospective study design to assess the effects of vitamin D from supplements and food on the risk of developing depressive symptoms. Subjects were post-menopausal women who had enrolled on the Women’s Health Initiative Observational Study and who were between 50 to 79 years at baseline. Depressive symptoms were assessed at baseline and at a follow-up 3 years later using the Burnam scale and medical records. Women with a food intake of vitamin D of over 800IU vitamin D/d had a prevalence odds ratio of 0.79 compared to women with a food intake of vitamin D of less than 100IU. Women without depression at baseline had a 20% lower risk of depressive symptoms if they had a food vitamin D intake over 400IU compared to under 100IU.
These results suggest that vitamin D intakes from foods are inversely associated with depression. However, the evidence from supplemental use of vitamin D was less consistent. This is interesting, because supplemental vitamin D should produce similar results when compared to food based vitamin D. This suggests that a confounding variable is possibly cause of the inverse association between vitamin D from food and the risk of depressive symptoms. Because vitamin D is present in so few foods, it is interesting to speculate about the possible confounding variable. Fish contains vitamin D and can be high in n-3 long chain polyunsaturated fatty acids. One of the fatty acids, docosahexanoic acid (DHA, C22:6 (n-3)) has been reported previously to benefit brain function and may be beneficial at preventing depression. Care should therefore be taken when analysing the data in this study.
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