On 2014 Feb 14, David Keller commented:

Sunshine, not vitamin D, combats depression

Depression is associated with vitamin D deficiency. However, vitamin D supplements do not reduce this depression because depression and vitamin D deficiency are both symptoms of the same underlying problem: lack of sun exposure. Exposing the skin to sunshine promotes endogenous synthesis of large amounts of vitamin D, and is the principal natural source of vitamin D for humans. Likewise, retinal exposure to sunshine prevents or treats depression, by stimulating certain endogenous brain neurotransmitters, which is why light-exposure therapy relieves seasonal affective disorder. These facts are all well established. Expecting vitamin D supplements to reduce depression in sunshine-deprived patients is analogous to treating their vitamin D deficiency with anti-depressants.

On 2014 Feb 14, David Keller commented:

Sunshine, not vitamin D, combats depression

Depression is associated with vitamin D deficiency. However, vitamin D supplements do not reduce this depression because depression and vitamin D deficiency are both symptoms of the same underlying problem: lack of sun exposure. Exposing the skin to sunshine promotes endogenous synthesis of large amounts of vitamin D, and is the principal natural source of vitamin D for humans. Likewise, retinal exposure to sunshine prevents or treats depression, by stimulating certain endogenous brain neurotransmitters, which is why light-exposure therapy relieves seasonal affective disorder. These facts are all well established. Expecting vitamin D supplements to reduce depression in sunshine-deprived patients is analogous to treating their vitamin D deficiency with anti-depressants.