Vitamin D Newsletter


Vitamin D Dosage

How much vitamin D should I take?

Before I answer, I have a few questions for you:

  • Where do you live (latitude)?
  • How much do you weigh?
  • What skin type do you have?
  • How much do you go into the sun?
  • What is your 25(OH)D level?
  • During what season of the year was it obtained?
  • How much do you get in your diet?
  • How much do you get in supplements?

You see, the answer is different for everyone. The question also assumes we know the ideal vitamin D blood level. We don't know for sure—around 50 ng/mL is the best current guess.

However, an easy answer is: 2,000 units a day. Life Extension Foundation sells an inexpensive pharmaceutical grade of vitamin D. Two-hundred and fifty of the 1,000 unit capsules cost about $10. Your local health food store should also carry 1,000 unit capsules. Just be sure they don't contain any vitamin A. Beta-carotene is okay, but pre-formed retinols (vitamin A) interfere with vitamin D's function. I do not advise cod liver oil; if you just have to take it, don't take more than 1 teaspoon per day. Get your omega-3s from molecularly distilled fish body oils (Trader Joe's) or by eating wild salmon or sardines. Get your vitamin D by taking vitamin D or by going into the sun, or by combining both.

The government says 2,000 units of vitamin D a day is safe for all adults to take without a doctors supervision. Two thousand units a day will get about 80% of Americans to a vitamin D level of 35 ng/mL or higher with no risk of toxicity. The 20% still lower than that would most likely be Blacks.

For now, if you take more than 2,000 units a day, you should do so either because you are under the care of a health care practitioner who is knowledgeable in regards to vitamin D (unfortunately, there are few of them), or because you know what you are doing. I personally take no vitamin D in the late spring, summer, or early fall because I frequently go into the sun. I take 5,000 units a day in the winter but I know what my vitamin D level is because I get it checked several times a year. If I had cancer, heart disease, Alzheimers disease, multiple sclerosis, or a hundred other common diseases, I might take more than 5,000 units a day—but I would check my calcium and vitamin D levels even more often. I would also follow my doctor's advice about standard medical treatment.

Keep in mind that if you use a sunlamp or a tanning parlor once a week during the winter, you don't have to worry about blood tests because your body will maintain adequate vitamin D blood levels. Just don't get burned.

Also, remember to take calcium tablets if you don't get adequate amounts of calcium in your diet—and most people don't. Trader Joe's sells a good Calcium/Magnesium/Zinc combination product for next to nothing.

Vitamin D Blood Test

What blood test should I have?

The only blood test that can determine vitamin D adequacy is a 25-hydroxyvitamin D test. Whenever I say "vitamin D level" I am talking about a 25-hydroxyvitamin D. Ask your doctor to order a 25-hydroxyvitamin D blood test.

Unfortunately, many doctors order an "activated vitamin D level," thinking it better to measure the most active form of vitamin D. It is not. Activated vitamin D, also known as 1,25 dihydroxyvitamin D or calcitriol, should never be obtained to determine vitamin D sufficiency. Calcitriol is often elevated in vitamin D deficiency. You cannot tell anything about your vitamin D nutrition by measuring a calcitriol level. If your doctor insists on ordering a calcitriol level to determine your vitamin D nutrition, find another doctor.

However, serious problems do exist with the technology used by some laboratories to measure vitamin D levels. Different labs will report different results when given the exact same specimen of blood. Furthermore, the same lab often reports significantly different numbers when sent the same specimen of blood at different times. In general, low numbers are more reliable than high numbers because interfering substances can easily give falsely elevated results. Prominent scientists have issued urgent calls for standardization. Dr. Graham Carter, one of my personal heroes, has dedicated his life to obtaining a standardized, and accurate, vitamin D level. His outfit in London is DEQAS, or Vitamin D External Quality Assessment Scheme. Call your reference lab and insist they participate in DEQAS. DEQAS's phone number in England is +44(0)2083833645.

If you take ergocalciferol, or "vegetarian vitamin D", be warned. Ergocalciferol is not vitamin D, but a vitamin D-like patent drug whose patent has expired. It does not normally occur in the human body and is probably a weak agonist at the receptor site, meaning it may actually partially block vitamin D actions. Ergocalciferol is the villain in most of the reported cases of toxicity in the world's literature. All bets are off in terms of measuring blood levels if you take ergocalciferol. Some of the labs can pick it up and some cannot. Do not take ergocalciferol—it is not vitamin D.

If your doctor prescribes 50,000 units of ergocalciferol (Drisdol) once or twice a week, obtain a bottle of 50,000 unit capsules of cholecalciferol and take them instead. Take one or two per week until your level is around 50 ng/mL. Then stop taking them and begin maintenance therapy at a much lower dose. You could also take one 5,000 unit capsule every day until your vitamin D level is around 50 ng/mL. Then take enough by mouth during the cold months (and go into the sun during the warm months) to keep your 25(OH)D level around 50 ng/mL. (Keep in mind that labs inside the USA usually report results in ng/mL while labs outside the USA use nM/L. One ng/mL is equal to 2.56 nM/L. So 50 ng/mL is about 125 nM/L.)

Take enough real vitamin D3 cholecalciferol to maintain your level around 50 ng/mL, year-round. A 25(OH)D level is the best, and only, way you have of knowing if you are taking enough. However, do not be satisfied with a 50 ng/mL level unless you know how you are getting enough vitamin D to explain the level (i.e., you go into the sun or take supplements). If your level is 50 ng/mL and you don't take supplements, don't go into the sun, don't use a sun booth or a UVB lamp, then the level is probably bogus. Repeat the level.

In general, keep your vitamin D level in the upper one third of the lab's reference range—about 50 ng/mL with the most commonly used test. If you take higher doses, get your calcium checked when you get your 25(OH)D level, just to be safe. If you want to be sure that your hospital is sending their samples to an accurate reference lab, ask the director of the hospital's lab to contact Professor Bruce Hollis or Professor Reinhold Vieth. Both are world-class authorities in vitamin D measurement technology.

Although 1,25-dihydroxyvitamin D (calcitriol) should never be used to diagnose vitamin D deficiency, calcitriol is important in evaluating one cause of high blood calcium, called vitamin D hypersensitivity. High blood calcium rarely occurs due to vitamin D toxicity, but calcium is elevated in people who have vitamin D hypersensitivity, although their vitamin D level will be normal, or even low. Primary hyperparathyroidism is a common cause of vitamin D hypersensitivity, as is sarcoidosis and other granulomatous diseases. It can occasional occur in cancer—about 20% of patients with non-Hodgkin's lymphoma have vitamin D hypersensitivity. Any competent endocrinologist can treat vitamin D hypersensitivity.

Effects of Higher Doses

If humans make 20,000 units of vitamin D after sunbathing for 20 minutes in the summer, why shouldn't I take 20,000 units every day?

Because of what we don't know we don't know. Someone once said all knowledge comes in three categories: (1) what you know you know, (2) what you know you don't know, and (3), the largest category, what you don't know you don't know. I know I know how to speak English; I know I don't know how to speak French; I don't know that I don't know how to speak a language that I don't know exists.

We simply don't know the effects of taking 10,000 or 20,000 units a day for year after year. Although light-skinned humans make about 50,000 of units of vitamin D after getting a sunburn (3 times the minimal erythemal dose), we also know they make progressively less and less vitamin D as their skin produces more and more melanin, thereby tanning. My 16-year-old daughter has noticed that she tans much faster when she has been taking oral vitamin D. That is, high blood levels may tell the skin to make more sunblock (melanin). Undoubtedly, other natural mechanisms exist to prevent toxicity, we just don't know. We do know that when healthy young men took 50,000 units of vitamin D every day for six weeks, average serum blood levels increased by 257 ng/mL. One young man achieved an increase of 400 ng/mL after only six weeks. Although the authors found no evidence of toxicity after this six-week experiment (serum calcium remained normal), 50,000 units a day will eventually turn your internal organs into limestone.

Vitamin D's Future

Where do you predict all this vitamin D research is heading?

I predict the final Food and Nutrition Board's recommendation (in about two decades) will be about 3,000 units a day. I predict that science will eventually show vitamin D deficiency is a major cause of many of the diseases of civilization. I predict that science will eventually show that many of these same diseases of civilization respond favorably to vitamin D treatment. I predict science will eventually prove vitamin D helps prevent and treat some infectious diseases, especially viral respiratory infections like influenza, croup, and the common cold. These are only my attempts to prophesize the future. Remember, only time can tell the difference between a prophet and a madman.

Page last edited: 06 November 2010