There is not a general consensus among researchers that vitamin D supplementation has a direct causal effect on the management of depression and anxiety symptoms.
Effects of Vitamin D in Managing Depression
Some researchers (Casseb et al.) examined a large number of relevant studies and concluded that many clinical studies have indicated that vitamin D supplementation is associated with the reduction of symptoms of depression and anxiety, particularly when the supplementation was carried out in individuals with a major depression disorder (MDD) diagnosis.
Some research finding summaries about the effects of vitamin D:
Higher dose of vitamin D associated with improvements in well-being vs. lower dose
Vitamin D and fluoxetine combination superior to fluoxetine alone in controlling depressive symptoms
Higher dose of vitamin D3 improved depression symptoms after 3 months
Vitamin D levels correlated with BDI-II scores, and vitamin D supplementation improved depressive symptoms in women
Supplementation decreased perinatal symptoms of depression
Improvement in depression scores, sleep quality and metabolic parameters such as homeostasis model of assessment-insulin resistance
Trend of less depression in “daily users” of vitamin D supplement
Mechanism of Vitamin D Effects
Although the underlying pathophysiology of vitamin D in depression is still not fully understood, some mechanisms of depression that are associated with vitamin D are as follows.
Vitamin D and neurotrophic hypothesis. Vitamin D could modulate neurotrophic agents, the abnormal function of which is believed to be associated with various psychiatric diseases.
Vitamin D and monoamine neurotransmission hypothesis. Vitamin D might be involved in depression by directly or indirectly influencing the levels of 5-HT, DA and NE.
Vitamin D and neuroimmunomodulation. Vitamin D may play a neuroimmunological role by regulating the activity and expression of P2X7R gene, thus protecting nerve cells and producing antidepressant effects.
No Consensus Among Researchers
Although some clinical studies have indicated that vitamin D may be useful for the management of symptoms of depression and anxiety disorders, there are also research studies that found no effects of vitamin D supplementation in relieving depression symptoms.
Moreover, many studies found vitamin supplementation is “associated” with reductions in depression symptoms, but researchers are not certain about the nature and direction of the causal relationship between vitamin D levels and anxiety and depression.
As an example, fibromyalgia is a complex problem in which symptoms of anxiety and depression feature prominently. Low levels of vitamin D have been frequently reported in fibromyalgia.
Researchers (Armstrong et al.) say that fibromyalgia patients with high levels of anxiety and depression are less exposed to sunlight and take less vitamin D in the diet; therefore, it may be the fibromyalgia which “causes” the low levels of the vitamin.
Geng, Chunmei, et al. “Vitamin D and depression: mechanisms, determination and application.” Asia Pacific Journal of Clinical Nutrition, vol. 28, no. 4, 2019, pp. 689-694.
Casseb, Gleicilaine A. S., et al. "Potential Role of Vitamin D for the Management of Depression and Anxiety." CNS Drugs, vol. 33, 2019, pp. 619–637.
Armstrong, D. J., et al. "Vitamin D deficiency is associated with anxiety and depression in fibromyalgia." Clinical Rheumatology, vol. 26, 2007, pp. 551–554.