Today's Livestrong newsletter broaches the topic of Vitamin D, something that I have been interested in ever since the Cancer Society of Canada suggested that large doses of Vitamin D can help prevent or fight cancer. Other health experts have suggested that Vitamin D deficiencies (hypovitaminosis D) of Canadians could be attributing to our higher instances of auto-immune disorders, like MS.
Vitamin D (commonly referred to as the "sunshine vitamin") plays an important role in both our physical and mental health. The vitamin is made by our bodies when our skin is exposed to direct ultraviolet rays from the sun for at least 20 mins at a time. The problem with living in Canada is that we don't get a lot of sunshine and we often don't go out in the sun unprotected (sunscreen hampers this process).
I can't recommend to you how much Vitamin D you should supplement your diet with as I am not an expert, but I can suggest to you to go off and research it yourself to determine what would benefit your lifestyle. Personally, in the winter I will take up to 1000 IU a day and in the summer I often drop it down to 400 IU a day and will sometimes even skip it (because I am a sun worshiper and often forget my sunscreen).
Vitamin D is one of only four vitamins that are stored by the body and as such we have been long taught not to take too much of it. This way of thinking is changing with new research and from what I've come to understand it would actually be difficult to ingest enough Vitamin D to produce toxicity (In healthy adults a sustained intake of 50,000 IU per day can produce toxicity after several months). Currently most information I've found suggests the "Tolerable Upper Limit" of Vitamin D is around 2000 IU per day.
Vitamin D is easy to obtain and take in pill form - I would suggest asking your pharmacist to recommend a trusted brand to you if decide to add a supplement to your diet.