Vitamin D is a fat-soluble vitamin that is found in eggs and fatty fish such as salmon and mackerel (and cod liver oil), eggs and fortified foods such as spreads and cereals, but your body can also make its own vitamin D after exposure to ultraviolet rays from the sun. The amount, however, is dependent on the season and your geographic location.
What is Seasonal Affective Disorder (SAD)?
Seasonal affective disorder (SAD) is a form of depression that usually begins in the autumn and continues throughout the winter months. Symptoms include feeling sad or anxious, fatigue, concentration problems, irritability and feelings of guilt and hopelessness.
Although the exact cause of SAD is unclear, numerous studies have suggested the condition may be triggered by lack of sunlight - this idea is supported by the fact SAD is more common among people who live at high latitudes or areas with lots of cloud cover.
One hypothesis behind SAD is that reduced sunlight exposure interferes with the body's biological clock that regulates mood, sleep and hormones. Another theory is that lack of sunlight causes an imbalance of neurotransmitters, such as dopamine and serotonin which are extremely important in regulating mood.
How is SAD linked to Vitamin D deficiency?
In a study conducted at the University of Georgia, researchers present the idea that vitamin D deficiency may be behind all of the theories related to SAD mentioned above.
The researchers identified that vitamin D levels in the body increase and decrease with the changing seasons in response to available sunlight. The researchers note that studies have shown there is a lag of about 8 weeks between the peak in ultraviolet (UV) radiation intensity and the onset of SAD - this correlates with the time it takes for UV radiation to be processed by the body into vitamin D.
Secondly, as vitamin D also plays a part in the synthesis of both dopamine and serotonin it is logical that there may be a relationship between low levels of vitamin D and depressive symptoms. This is supported by studies that have found depressed patients commonly had lower levels of vitamin D.
The researchers also believe there is a link between skin pigmentation and vitamin D levels, which may affect an individual's risk for SAD. They explain that studies have shown that people with darker skin pigmentation are at greater risk of vitamin D deficiency.
Co-author of the research Michael Kimlin, of the Queensland University of Technology, added "What we know now is that there are strong indications that maintaining adequate levels of vitamin D are important for good mental health."
How much Vitamin D should you be taking?
Recent research on vitamin D indicates that many people are deficient in this key vitamin. Further to this Dr. John Cannell, founder of the Vitamin D Council considers the vitamin D guidelines to be too low. He recommends taking 5,000 IU daily until your level is where it should be - vitamin D status can be measured by a simple blood test and it may be an idea to test this every few months if you do have inadequate levels in your body.
A typical maintenance dose ranges from 2,000 to 5,000 IU per day. When supplementing, be sure to take vitamin D3 (cholecalciferol) and NOT Vitamin D2 (ergocalciferol). The latter is the synthetic form which is not effective.
A tip to take away - recent research suggests that it's most effective to take vitamin D with your largest meal!
Please note that a great deal of research is being conducted on the health benefits of vitamin D, and it's a controversial topic, so recommendations in regard to ideal level, dose and timing may change. The Vitamin D Council is a good resource for all the latest research findings.