After reviewing over 100 articles on vitamin D and seasonal affective disorder (SAD), an international team of researchers hypothesizes that a lack of vitamin D may play a foundational role in the development of SAD. SAD is a form of seasonal depression that strikes in the fall and winter months. The researchers published their conclusions in the journal Medical Hypotheses. They suggest several reasons as to why changes in vitamin D levels during the winter may be a key cause of SAD, rather than simply one factor among others, including:
Vitamin D levels vary in accordance with changes in sunlight and the onset of SAD.
Lower vitamin D levels have been found in depressed individuals, compared to controls.
Vitamin D affects the levels of serotonin and dopamine in the central nervous system, which has been linked to depression.
Vitamin D is concentrated in regions of the brain containing circadian timing systems, which have also been associated with SAD.
In addition to this new research, some, but not all, human trials have found that taking vitamin D improves mood in individuals both with and without SAD. In one study, mood improved in people without SAD when they took 400-800 IU per day, for five days. In another study, mood improved in people with SAD when they took a very large, one-time dose of 100,000 IU. Nevertheless, always be sure to talk to a health care practitioner before starting a new supplement, especially if you intend to take a large dose, or one that is higher than what is recommended on the label.
Source: Medical Hypotheses