For years, vitamin D was the Rodney Dangerfield of the nutrition world: It got no respect.
Vitamin D was viewed as a nutrient necessary in children to prevent rickets, a small quantity necessary to prevent osteopenia (bone-thinning) in adults. Mothers forced foul-tasting cod liver oil on their children. End of story.
But today anyone engaged in Web-based health conversations or reading the newspapers can't help but stumble across many of the unexpected and wonderful new observations surrounding vitamin D: reduction in risk for colon, breast, and prostate cancer; improvement in bone density and improvement in arthritis; reduction in heart attack risk; reductions in falls and fractures; improved memory and clarity of thinking; reduction of blood sugar; reduction in blood pressure, and on and on.
I can personally attest to most of these effects, now that I have helped about 1000 patients replace vitamin D.
But a very common question from people: "How much vitamin D should I take?"
The media are quick to say such things as "Take the recommended daily allowance of 400 units per day," or "Perhaps intake of vitamin D should be higher, maybe 2000 units per day." Or "Be sure to get your 15 minutes of midday sun."
The Food and Nutrition Board of the Institute of Medicine has been struggling with this question, also. They have tried to make broad pronouncements on American requirements for various nutrients by recommending Recommended Daily Allowances (RDA). The Food and Nutrition Board break vitamin D requirements down by age and sex, little better than a one-size-fits-all approach.
First of all, much of the confusion over dosing stems from the fact that vitamin D should not be called a "vitamin." We think of vitamins as nutrients our bodies were meant to obtain from foods. But, outside of oily fish, there is very little naturally-occurring vitamin D in food. (Even in fish, there is generally no more than 400 units per 4 oz. serving.) Sure, there's 20 units in an egg yolk, 100 units per 8 oz of milk because the USDA mandates it, and you can activate the vitamin D in a shiitake mushroom by exposing it to ultraviolet radiation, but those sources hardly help at all.
Vitamin D is better regarded as a hormone, not a vitamin. Vitamin D exerts potent effects in tiny quantities with hormone-like action in cells. It is the only hormone that is meant to be activated by sun exposure of the skin, not obtained through diet. As with any other hormone, such as thyroid hormone, doses should be individualized.
Imagine you developed a severely low thyroid condition that resulted in 30 lbs weight gain, losing your hair, swelling of your legs, and acceleration of heart disease. Would you accept that you should take the same dose of thyroid hormone as every other man or woman your age, regardless of your body size, proportion of body fat, metabolism, genetics, race, dietary habits, and other factors that influence thyroid hormone levels? Of course you wouldn't. Then why would anyone insist that vitamin D be applied in a one-size-fits-all fashion?