Vitamin D - How Much? What Source?
~ March 2009 No.224 ~
Vitamin D has recently been getting much attention as data is showing that this fat soluble vitamin may be involved in a variety of disease processes. An adequate supply of vitamin D is necessary for good bone development. People who are low in vitamin D may have increased risk of hypertension, diabetes and some (colorectal, breast, prostate) cancers; autoimmune diseases, such as multiple sclerosis, or rheumatoid arthritis may also have a vitamin D component
The Dietary Reference Intakes on the Health Canada website recommends between 200 and 2000 IU/day. However, as a result of the recent studies on vitamin D status and health, nutritionists are starting to encourage intakes at the higher intake range. Vitamin D can build up to toxic levels in the body, so some caution is needed
Synthesis in the skin involves UVB radiation that converts 7-dehydrocholesterol to pre-vitamin D3. In the body, pre-vitamin D3 metabolised to 25-hydroxycholecalciferol or 25(OH)D3. The two most important factors that govern the generation of pre-vitamin D3 are the quantity (intensity) and quality (appropriate wavelength) of the UVB irradiation. The pigmentaton in your skin also affects the amount of Viamin D you can produce; people with light skin are able to absorb more Vitamin D producing sunlight, and therefore can produce more natural Vitamin D.
People who live in the northern latitudes, where the hours of sunlight are reduced in the winter season, need to be aware that they may not be producing adequate Vitamin D via skin exposure. Also, people who follow customs that require the covering of the entire body need to be aware that that their natural production of Vitamin D will be compromised.
There is no risk of producing an overdose of vitamin D by exposure to sunlight because the skin's capacity to produce vitamin D is self-limiting - production stops when sufficient is produced.
Although some foods such as milk now contain added Vitamin D, there is mounting evidence that we require even higher levels to prevent a variety of diseases. In many cases, family doctors are recommending supplements to increase the intake of this important vitamin. But remember, Vitamin D is a fat soluble vitamin - it needs fat to be absorbed. Take your Vitamin D supplement with your meal.
Dietary Reference Intakes Health Canada