Vitamin D + You: Not a Vitamin, and Not One Size Fits All
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?
In truth, the ideal replacement dose of thyroid hormone can range widely from one person to another. Some people require 25 mcg per day; others require 800% greater doses. Likewise, vitamin D requirements can range widely. I have used anywhere from 1000 units per day, all the way up to 16,000 units per day before desirable blood levels were achieved.
Vitamin D dosage needs to be individualized. Factors that influence vitamin D need include body size and percent body fat (both of which increase need substantially); sex (males require, on average, 1000 units per day more than females); age (older need more); skin color (darker-skinned races require more, fairer-skinned races less); and other factors that remain ill-defined.
But these are "soft" rules. While in my office experience with 1000 patients on vitamin D the average female dose is 4000-5000 units per day, the average male dose is 6000 units per day to achieve a blood level of 60-70 ng/ml (somewhat higher than I've advocated in past), there are frequent exceptions of all stripes. I've had 98 lb women who require 12,000 units, 300 lb men who require 1000 units, 21-year olds who require 10,000 units.
Let me reiterate: Vitamin D dose needs to be individualized.
There's only one way to truly individualize your need for vitamin D and thereby determine your dose: Measure a blood level.
Nobody can gauge your vitamin D need by looking at you, nor by your skin color or other simple measurement like weight or body fat. A vitamin D blood level needs to be measured specifically─period.
Unfortunately, many people balk at this, claiming either that it's too much bother or that their doctor refused to measure it.
I would rank normalizing vitamin D as among the most important things you can do for your health. It should never be too much bother. And if your doctor refuses to at least discuss why he/she won't measure it, then it's time for a new doctor. If you're worried about adding to rising healthcare costs by adding yet another blood test, think of all the money that could be saved by sparing you from a future of cancer, heart disease, osteoporosis, diabetes, etc. The cost of a vitamin D blood test is relatively trivial (around $40-50.)
So, how much vitamin D should you take? Enough to raise your blood level of 25-hydroxy vitamin D to normal. (We aim for a normal level of 60-70 ng/ml.)