Jun
28
Summer Sun and Vitamin D
Jun 2011
By Maureen Williams ND
Vitamin D for healthy bones and more
Why all the fuss about vitamin D? It's long been known that vitamin D helps us to absorb the right amount of dietary calcium and use it to mineralize bone, and deficiency can lead to bone deformities in children and low bone density and increased fracture risk in adults. In recent years, the list of roles we recognize for vitamin D has grown to include mitigating inflammation, keeping the immune system strong, preventing cancerous changes in cells, and keeping nerve and muscle cells healthy.
How do we get enough vitamin D?
Amazingly, our bodies can manufacture all the vitamin D we need from chemicals made in sun-exposed skin cells. We also get vitamin D from eating fish, eggs, and fortified dairy products and cereals, but most of us need the sun or a supplement in order to get enough.
Here are some things to consider:
- The ultraviolet B (UVB) rays needed for vitamin D production are blocked to varying degrees by sunscreen, clothing, clouds, and pollution.
- UVB rays can't pass through glass, so getting sun through the windshield while driving will not increase your vitamin D production.
- Pigments in the skin reduce vitamin D production, so people with dark skin need more sun to make adequate amounts of vitamin D.
- For people living in northern latitudes (like Canada), it is virtually impossible to make adequate amounts of vitamin D in the fall and winter.
If you are fair-skinned, have most of your skin exposed, and aren't using sunscreen, your skin has the capacity to make about 1,000 IU per minute in the middle of a sunny mid-summer day, BUT, lots of factors affect how much D you can make, including how much D you already have in circulation. So, bearing in mind that these are exactly the conditions that put us most at risk of skin cancer, go ahead and get some summer sun-but not too much. Ten to fifteen minutes a day is enough.
Choosing the right supplement
Accepting that most of us don't get enough vitamin D from sun and food, it makes sense to consider supplementing, especially in the winter. The most common form of D used in supplements and food fortification is a synthetic variety called vitamin D2, or ergocalciferol. It is also the only available prescription form of vitamin D. The form of D your body makes, however, is vitamin D3 (cholecalciferol). D3 has been found to raise tissue stores of vitamin D three times as fast as D2. If you want to get the most for your money, or if you are using vitamin D to treat a health condition, look for D3.
[Interesting fact: Animals with fur or feathers don't have sun-exposed skin. Instead, sunlight converts a chemical in the oily secretions in their fur and feathers into vitamin D, and they ingest the vitamin while grooming. Vitamin D3 for supplements is extracted from wool fat that has been exposed to ultraviolet light.]
Testing
Vitamin D breaks down into more than 50 chemicals. One of these-25-hydroxy-vitamin D, or 25(OH)D-is stable enough to be accurately measured in the lab, so this is the test you will get if your doctor wants to check your vitamin D status. There are a few problems with this test:
- Different labs use different methods and get remarkably different results when looking at the same blood samples.
- 25(OH)D levels appear to change very little in some people taking high dose supplements and in some people getting lots of sun in the tropics, suggesting that the relationship between the test result and actual vitamin D status may be more complex than we would wish.
So, until a more reliable test becomes available, it is safe to assume (without testing) that healthy Canadians could use extra D in the winter, and maybe all year.
How much should we take?
In the face of a growing body of evidence that low vitamin D levels leave us at increased risk of heart disease, some autoimmune diseases, some cancers, and possibly diabetes and depression. Officials in the US have recently increased their recommendation for daily intake to 600 International Units (IU) per day for adults and children over one year old and 800 IU for seniors over 70. The Canadian Cancer Society recommends 1,000 IU/day in the winter, as well as the summer if you cover up or use sunscreen all the time or if you have dark skin.
What does the research show? Up to 4,000 IU/day (and probably more) is safe for healthy adults, and 1-2,000 IU/day appears likely to be enough to keep us optimally healthy.
Dr. Williams earned her Doctorate in Naturopathic Medicine from Bastyr University in Seattle in 1995. She is a researcher and writer and has worked in private practice in Vermont and Cortes Island. She now sees patients at the Co-operative Community Health Centre at James Bay and at Cook Street Village Health Centre. www.maureenwilliamsnd.com