“How much vitamin D should I take?” 22. August 2008 William Davis (17) It’s probably the number one most common question I get today: “How much vitamin D should I take?”Like asking for investing advice, there are no shortage of people willing to provide answers, most of them plain wrong. The media are quick to offer advice like “Take the recommended daily allowance of 400 units per day,” or “Some experts say that intake of vitamin D should be higher, as high as 2000 units per day.” Or “Be sure to get your 15 minutes of midday sun.”Utter nonsense. The Food and Nutrition Board of the Institute of Medicine has been struggling with this question, also. They have an impossible job: Draft broad pronouncements on requirements for various nutrients by recommending Recommended Daily Allowances (RDA) for all Americans. The Food and Nutrition Board has tried to factor in individual variation by breaking vitamin D requirements down by age and sex, but what amounts to a one-size-fits-nearly-all approach. Much of the uncertainty over dosing stems from the fact that vitamin D should not be called a “vitamin.” Vitamins are nutrients obtained from foods. But, outside of oily fish, you'll find 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 and you can activate the vitamin D in a shiitake mushroom by exposing it to ultraviolet radiation. Dairy products like milk (usually) contain vitamin D because the USDA mandates it. But food sources hardly help at all unless you’re an infant or small child. It all makes sense when vitamin D is viewed as a hormone, a steroid hormone, not a vitamin. Vitamin-no, steroid hormone-D exerts potent effects in tiny quantities with hormone-like action in cells, including activation of nuclear receptors. It is the only hormone that is meant to be activated by sun exposure of the skin, not obtained through diet. But the ability to activate D is lost by the majority of us by age 40 and even a dark tan is no assurance that sufficient skin prohormone D activation has taken place. As with any other hormone, such as thyroid, parathyroid, or growth hormones, dose needs to be individualized. Imagine you developed a severely low thyroid condition that resulted in 30 lbs of weight gain, lose your hair, legs swell, and heart disease explodes. 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? (There’s another world in which a one-size-fits-all approach to hormone replacement has been widely applied, that of female estrogen replacement. In conventional practice, there’s no effort to identify need, estrogen-progesterone interactions, nor assess the adequacy of dose, not to mention the perverse non-human preparation used.) With thyroid hormone, ideal replacement dose of hormone ranges widely from one person to another. Some people require 25 mcg per day of T4; others require 800% greater doses. Many require T3, but not everybody. 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 dose 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 “rules” often broken. My office experience with vitamin D now numbers nearly 1000 patients. The average female dose is 4000-5000 units per day, average male dose 6000 units per day to achieve a blood level of 60-70 ng/ml, though there are frequent exceptions. 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. (Of course, this is a Wisconsin experience. However, regional differences in dosing needs diminish as we age, since less and less vitamin D activation occurs.)Let me reiterate: Steroid hormone-vitamin D dose needs to be individualized. There’s only one way to 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, by your skin color, size, 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 steroid hormone-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 the money 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, a fraction of the cost of a one month supply of a drug for diabetes.) 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.)