We don’t yet know whether taking a vitamin D supplement will definitely help in the treatment or prevention of depression. The exact relationship between vitamin D levels and depression is still unclear and more research needs to be carried out, particularly in patients with depression and low levels of vitamin D.

Low levels of vitamin D have been observed in patients with depression and are thought to increase the risk of developing depression in later life. However, there is debate about whether low levels of vitamin D contribute to the development of depression, or whether patients with depression develop a vitamin D deficiency because, for example, they spend less time outdoors. Most of the vitamin D that our body needs is made when our skin is exposed to the sun. Any illness that decreases the amount of time we spend in the sun can have an impact on our vitamin D levels.

So far research has produced conflicting results. One systematic review and meta-analysis suggested that taking a vitamin D supplement may help reduce the symptoms of depression in patients with clinically significant depression. However, in another study taking a vitamin D supplement had no effect on the symptoms of depression in older patients with clinically relevant depression.

More research needs to be conducted to overcome the limitations of the previous studies. The Vitamin D and OmegA-3 TriaL (VITAL) is one such study that is ongoing in the U.S. It is being conducted in 25,871 men and women and is looking at whether vitamin D3 (2000 IU) or omega-3 fatty acids (Omacor® fish oil, 1 gram) supplementation can lower the risk of developing depression and other conditions. To date, the VITAL study has found that taking a vitamin D3 supplement does not lower your risk of cancer, heart attack, stroke or dying from a cardiovascular event. It was found, however, to lower your risk of dying from cancer.