Have there been any studies on the changes in Vitamin D levels over the course of a year – presumably people will have lower levels in winter.
How do we know how much vitamin D people get from sun? Most of us are city dwellers and spend very little time outdoors, regardless of the season. On top of this, we have all been told to stay out of the sun or use sun screen to avoid skin cancer.
Recommendations regarding vitamin D supplementation have been cautious, but the same caution was not used in devising recommendations regarding sun exposure. We are told to avoid the sun at all costs and wear sunscreens, some of which contain chemicals whose safety is questionable.
Would it not have been more prudent to encourage people to get some sun exposure, but not too much, instead of encouraging us to avoid the sun altogether? We seem to have evolved to require sun exposure for our health, and there is still a great deal we don’t know about its importance to our wellbeing.
Vitamin D is needed for bone and cardiovascular health, as well as to prevent certain forms of cancer. Low levels are thought to play a role in the development of Multiple Sclerosis. It is also important for immune function, and may explain why influenza levels are higher in winter. Vitamin D also activates genes that regulate brain function, which may explain the high prevalence of depression in late winter, when vitamin D levels are lowest.
Check out Emily Deans’ blog, including this article on vitamin D and depression: http://evolutionarypsychiatry.blogspot.ca/2010/07/d-d-depression.html