Depression is a serious lifestyle disease that often has no known cause. Treatment of depressive symptoms can be highly difficult as no clear mechanism of development has been explained. This suggests that depression is multifactorial and a large number of factors can influence its development. Increasingly, the Western diet is being associated with development of depression. This relates to the inability of the Western diet to supply adequate amounts of many nutrients, some of which may be required for mental health. One nutrient that may play a central role in the development of depression is vitamin D. Western populations have a high incidence of depressive symptoms and a high incidence of vitamin D deficiency. Based on this observations a number of studies have investigated the relationship between vitamin D and depressive symptoms in Western populations. Results from these studies have confirmed that there exists an association between low levels of vitamin D and the development of depressive symptoms.
Receptors for vitamin D are present on neurones in many areas of the brain, suggesting that vitamin D is required for normal neuronal function. In particular vitamin D receptors are present in the cingulate cortex and the hippocampus, two areas of the brain that are thought to be involved in the development of depression. Vitamin D is known to play a central role in a number of important physiological processes that may explain its association with depression, including brain development, neuroimmunomodulation, neuroprotection, the regulation of neuronal growth and neuroplasticity. Vitamin D receptors are also known to be present in the promoter regions of serotonin genes, indicating vitamin D may be required for serotonin synthesis. A deficiency of vitamin D may therefore affect all of these functions, particularly in the cingulate cortex and the hippocampus, and this may be a contributory factor in the development of depressive symptoms. The association between poor vitamin D status and depressive symptoms may explain the mood deterioration often experienced during long periods where sunlight exposure is not possible.
Associations are interesting, but they do not confirm a cause and effect. Therefore clinical studies have been used to investigate the effects of vitamin D supplementation on depressive symptoms. In one such study, researcher administered 20,000 or 40,000 IU of vitamin D3 (cholecalciferol) per week (2857 or 5714 IU vitamin D per day, respectively) to subjects with depressive symptoms. The length of the study was 1 year. Subjects with 25-hydroxyvitamin D levels below 40 nmol/L scored higher for depressive traits compared to those subjects with 25-hydroxyvitamin D above 40 nmol/L. In the group given vitamin D supplements there was a significant improvement in the depressive symptoms experienced by the subjects, and this was most evident in those with the most severe depressive scores (and the lowest 25-hydroxyvitamin D levels). Therefore vitamin D supplements may provide relief from depressive symptoms and this effects might be most pronounced in those with the most severe depression.
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