Vitamin D plays an important mood-regulating role in humans, a team of scientists has discovered.

An international team of scientists has found a link between the onset of Seasonal Affective Disorder - primarily a winter-time depression-like affliction - and lack of vitamin D.

Sunlight, a natural source of vitamin D, is not as abundant in winter months, especially in higher elevations where there may be increased cloud formations.

Alan Stewart of the University of Georgia, and his team, said one theory behind SAD is that reduced sunlight interferes with the body's internal clock. The internal clock regulates sleep, hormones and mood.

Stewart's team also suggested that lack of sunlight leads to an imbalance in the neurotransmitters dopamine and serotonin, which are responsible for regulating mood, according to a report published in Medical News Today.

The study is significant in that it shows that the amount of vitamin D in the body has a direct relationship to the onset, strength and duration of the affliction.

"Vitamin D likely functions in a more foundational and regulative role in potentiating the sub-mechanisms associated with the depressive and seasonality factors," the researchers said.

Michael Kimlin of the Queensland University of Technology in Australia, a co-author of the study, said Vitamin D plays a crucial role in the synthesis of serotonin and dopamine. Low levels of these neurotransmitters have been associated with depression, Disabled World reported.

The study is not the first to research the relationship between Vitamin D and mental health. Last July, a scientist and his team at Isfahan University of Medical Sciences in Iran found that participants lacking vitamin D were 2.16 times more likely to have schizophrenia than participants with normal vitamin D levels.

Findings on the subject have been published in the journal Medical Hypotheses.