Increased levels of anxiety and depression during winter months occur in the normal population and are most likely related to short days with lower light levels. Some individuals are very sensitive to this decrease in sunlight and thus develop seasonal affective disorder (SAD), or "winter depression." More than 80 percent of SAD sufferers are women with an age of onset generally in the third decade. Symptoms of SAD include carbohydrate craving, hypersomnia, lethargy, and changes in circadian rhythms. Several theories have been proposed to explain SAD including disrupted circadian rhythms, delayed circadian rhythms, low levels of serotonin, and low levels of melatonin.
Could a lack of vitamin D also play a role in "winter depression?" Vitamin D is a steroid synthesized in the skin by conversion from 7-dehydrocholesterol in response to ultraviolet B radiation and subsequently undergoes hydroxylations in liver and kidney to become the active hormone 1,25-dihydroxyvitamin D3.
Researchers from the Department of Psychology, The University of Newcastle in Callaghan, New South Wales, Australia, gave forty-four healthy subjects 400 units, 800 units, or no vitamin D3 for five days during late winter in a randomized, double-blind study. Results on a self-report measure showed that vitamin D3 significantly enhanced positive affect and there was some evidence of a reduction in negative affect.
Even though this was a very short-term study, adding 400 units to vitamin D to the regimen of someone who suffers with SAD appears to be a good idea. Could everyone benefit to some degree from additional D3 in the winter? Perhaps, but this is difficult to say for certain at this time.
Lansdowne L, Provost S. Vitamin D3 enhances mood in healthy subjects during winter. Psychopharmacology 135:319-323, 1998.