Concerns about Vitamin D deficiency may bring up an interesting dilemma. Those of us who live outside the tropics, don't eat enough of the foods that naturally have Vitamin D in them, spend little time outside four walls, use sunscreen or even have factors that inhibit normal absorption -- may be deficient in Vitamin D.
RDA's were set to define minimum levels to prevent deficiency conditions -- short on D = rickets. Who would have thought that Vitamin D's functions go far beyond bone health? Studies are piling up with benefits for high blood pressure, autoimmune disease, and cancer and diabetes prevention, to name a few. Other studies show that low levels of D are common.
So what do we do? Eat fatty fish and egg yolks, take cod liver oil, and cautiously get just enough sun. It would be hard to get too much D from food or the sun, but what about supplements? Canadian advisers have already increased the recommended daily intake from 400 IU to 1000 IU, and experts in the US want the FDA to do so too. "Upper levels" have been set higher already. Supplements can fill that gap.
All this seems to be a good move. Increase Vitamin D intake, understand the crucial interaction of D, calcium, magnesium, Vitamin K, and other co-factors and make sure we're getting enough (but not too much). Now my question is -- are we changing the meaning of the RDA (or whatever incarnation it's in now)? Are we proposing a move from minimum nutrition to prevent rickets (or whatever) to a new view that would realistically promote real health?
Another possibility: if Vitamin D can prevent a specific condition, or improve a condition, does that qualify that condition as a deficiency disorder? Cancer? Arthritis? Alzheimers? At the very least, we are certainly reinforcing this truism: Eating well is the best revenge!
THINK AGAIN -- Recommendations for Vitamin D usually specify D3, the natural form found in fish oils and lanolin. D2, either synthetic or from other natural sources, is said to be absorbed only about 1/2 as well. Or is it? A recent study from Boston University found that blood levels are the same when either form is used. In Australia, a study showed fewer falls in elderly women using D2. Stay tuned...