Harvard Health Letter | June 2007
A more D-manding diet
Some experts say we should have a lot more vitamin D in our diets because it’s protective against several diseases.
Vitamin D has long been recognized as vital to bone health because the body needs the vitamin to absorb calcium. But research has suggested that it may be good for a lot more than just bones. Ample intake of vitamin D may help fend off a wide range of conditions, including colon cancer, diabetes, and physical weakness in old age. Meanwhile, another batch of studies has found that many people, especially as they grow older, have low levels of vitamin D in their blood. Our skin has an amazing ability to produce vitamin D when it’s exposed to sunlight, but with age, the skin becomes less productive. The problem is made worse by older people spending more time indoors. Rickets is the classic children’s disease caused by vitamin D deficiency. It has re-emerged as a problem in some African American communities.
Because of the evidence for shortfalls and the possibility of added benefits, some experts think the recommendations for vitamin D are set way too low. The vitamin D enthusiasts say adults should be getting at least 1,000 IU (International Units) a day. The committees of experts convened by the
The experts — who include Dr. Walter C. Willett, chair of the Harvard School of Public Health’s nutrition department — noted that 400 IU doesn’t increase the amount of vitamin D circulating in the blood very much. Depending on how much a person started out with, they said a daily intake of about 2,000 IU — the upper limit — is necessary before blood levels get high enough for vitamin D to have its full disease-fighting effects.
Current vitamin D guidelines
71 and older
The daily intake for adults recommended by some experts is 800–1,000 IU.
the Sun as a Source of Vit D
That’s a lot of vitamin D. Expanding and increasing fortification would be one way to increase intake. In the
Now getting more sun exposure is another, more controversial, way to increase vitamin D levels, because it means changing the advice to avoid sun and wear sunscreen to protect against skin cancer and other forms of skin damage. Some analysis shows that any increase in skin cancer from adding a small amount of unprotected sun exposure would be offset by declines in other forms of cancer that it might reduce.
Some vitamin D researchers want to see “safe sun” recommendations that would actively encourage people to get 15 minutes or so of sun a few times a week — without sunscreen, which blocks the UV radiation that triggers vitamin D production in the skin.
The pressure to revise vitamin D recommendations is building. The American Cancer Society is preparing its first comprehensive set of guidelines for skin cancer prevention. So stay tuned.
There’s been a lot of disappointing news about vitamins, but vitamin D stands out as a bright spot.
It looks like we need to start thinking about short exposures to Sun as another factor on our healthy lifestyle list. It seems almost intuitive that the Sun, being an integral element of energy in our world, much like water, should have a part in keeping us healthy. So start asking yourself the following questions every so often:
- How often are you getting Sun exposure per week?
- Is it more than 15 minutes?
- Are you protecting your skin if its more than 15 minutes?