People with seasonal affective disorder dread the approach of fall and winter. They become blue and depressed during the winter months when the days are short. The cause may be a deficiency of vitamin D due to a lack of sunlight.
Researchers reviewed the findings from more than 100 articles in medical journals and found a relationship between vitamin D and seasonal affective disorder, which is sometimes (and aptly) called SAD.
Vitamin D is made through a reaction of ultraviolet light on a precursor chemical in the skin. It is also found in oily fish and cod liver oil, and it often added to milk. Levels of vitamin D in the bloodstream fluctuate with the seasons in direct relationship to available sunlight.
Studies have shown that there is a lag of about eight weeks between the peak in intensity of ultraviolet radiation in sunlight and the onset of seasonal affective disorder. This lag time correlates with the time it takes for UV radiation to be processed by the body into vitamin D.
Vitamin D is involved with the synthesis of serotonin and dopamine in the brain. Low levels of both of these brain chemicals are linked to depression. It is also important for maintaining bone health. Serious vitamin D deficiency can result in softening of bones, a condition called osteomalacia, or rickets.
"Evidence exists that low levels of dopamine and serotonin are linked to depression, therefore it is logical that there may be a relationship between low levels of vitamin D and depressive symptoms," said Michael Kimlin of the Queensland University of Technology and one of the authors of the study.
The body only needs a few minutes of exposure to sunlight a day to make the vitamin D that it needs. People with darker skin do not process vitamin D as quickly as those with paler skin.
The review was done by researchers from the University of Georgia, The University of Pittsburgh, and the Queensland University of Technology in Australia. It was published in the journal Medical Hypotheses and reported on at Science Daily.com.