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Answers to Vitamin D Questions from a Leading Physician

John Cannell, M.D. answers some basic questions about the hottest nutrient topic in nutrition research

by Craig Weatherby

The following Q&A comes from the July, 2008 edition of the Vitamin D Council newsletter.

Written by nutrition-savvy physician John Jacob Cannell, M.D., the Council's newsletter never fails to enlighten in refreshingly frank fashion.

Fish fit the vitamin D bill; Sockeye salmon stand out

Certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.

Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:

Vitamin D per 3.5 ounce serving*

Sockeye Salmon687 IU

Albacore Tuna544 IU

Silver Salmon430 IU

King Salmon236 IU

Sardines222 IU

Sablefish169 IU

Halibut162 IU

*For our full test results, click here.

We've edited it for length by leaving out some questions about the differences in vitamin D tests. For the full version, look in the Vitamin D Council publication archives. (As of today, the current issue was not yet posted, but it should be up on this page soon.)

Dr. Cannell also wants us to know that this past March, the The Toronto Globe and Mail printed what he considers the best press article ever written about vitamin D, titled “The vitamin D miracle: Is it for real?

Here's the Q&A with Dr. Cannell, from the The Vitamin D Newsletter for July, 2008:

1. How much vitamin D should I take?

I don't know.

2. How often should I have a 25-hydroxy-vitamin D blood test?

I don't know.

3. Why don't you know?

The reason I don't know is that everyone's situation is either a lot, or at least a little, different.  How much vitamin D you need varies with age, body weight, percent of body fat, latitude, skin coloration, season of the year, use of sunblock, individual variation in sun exposure, andprobablyhow ill your are.

As a general rule, old people need more than young people, big people need more that little people, fat people need more than skinny people, northern people need more than southern people, dark-skinned people need more than fair skinned people, winter people need more than summer people, sunblock lovers need more than sunblock haters, sun-phobes need more than sun worshipers, and ill people may need more than well people.

Regular readers should understand the reasons behind all these statements except for the last one. However, don't feel bad, no one understands it.  Vitamin D is used by the body, metabolically cleared, both to maintain wellness and to treat disease.

This is what I'd do. If you live in Florida and sunbathe once a week, year around, do nothing. If you use suntan parlors once a week, do nothing. However, if you have little UVB exposure, my advice is as follows:

  • Well children under the age of two should take 1,000 IU per day, over the age of two, 2,000 IU per day.
  • Well adults and adolescent between 80 pounds and 130 pounds should start with 3,000 IU per day, over 130 pounds but less than 170 pounds, 4,000 IU per day and over 170 pounds, 5,000 IU per day.

Two months later have your doctor order your first 25-hydroxy-vitamin D blood test.  Yes, start the vitamin D before you have the blood test. Then adjust your dose so your 25(OH)D level is between 50 and 70 ng/ml, summer and winter.  These are conservative dosage recommendations.

Most people who avoid the sunand virtually all dark-skinned peoplewill have to increase their dose once they find their blood level is still low, even after two months of the above dosage, especially in the winter.

One more thing. Everyone has different vitamin D machinery. For example, regular run-of-the-mill rickets does not require much vitamin D to be cured. However, two other forms of rickets, both rare, one caused by a defective vitamin D receptor and the other by a malfunction of the enzyme that activates vitamin D, requires either much more vitamin D or activated vitamin D (calcitriol) itself.

It seems likely that there is as much variation in the amount and functionality of the enzyme that activates vitamin D as there is in the vitamin D receptor. Furthermore, there are probably tissue variations as well. That is, one vitamin D deficient child gets rickets, another autism, another asthma, and yet another type-1 diabetes because functionality of the vitamin D machinery is genetically variable both between children and within children's tissues.

Therefore, some people, who have genetically determined decreased functionality of the machinery in different tissues, will need more vitamin D. How much more, we do not know. However, should you have a child with autism, they will usually need more than a normal child to overcome their genetic defects.  None of what I say in this last paragraph has been proven, it is theoretical.

4. What blood test should I have?

The only blood test that can diagnose vitamin D deficiency is a 25-hydroxy-vitamin D [25(OH)D]. Get your levels above 50 ng/ml, year around.

Unfortunately, about 10-20% of the doctors in the USA order the wrong test. They order a 1,25-dihydroxy-vitamin D, thinking that by measuring the most potent steroid in the system, they are getting useful information. They are not. 1,25-dihydroxy-vitamin D is an adaptive hormone; it goes up and down with calcium intake.  Furthermore, as 25(OH)D is a weak steroid, when 25(OH)D levels are low, the body compensates by increasing the amount of the potent steroid, 1,25-dihydroxy-vitamin D.

Thus, a common cause of high 1,25-dihydroxy-vitamin D is low 25(OH)D or vitamin D deficiency. So these doctors see the 1,25-dihydroxy-vitamin D is normal or high and tell their patients that they are OK when they are vitamin D deficient, advice that may prove fatal.

Furthermore, the reference labs in this country know this is occurring but, to date, have not taken steps to educate the doctors ordering the test because the reference labs make more money off a 1,25-dihydroxy-vitamin D than they do from a 25-hydroxy-vitamin D.

Although the misdiagnosis of vitamin D deficiency may prove fatal, the doctors, and the reference labs, are ordering and processing the wrong test.

5. Where should I get my vitamin D supplements?


6. What is the ideal level of 25(OH)D?

We don't know. However, thanks to Bruce Hollis, Robert Heaney, Neil Binkley, and others, we now know the minimal acceptable level. It is 50 ng/ml.  In a recent study, Heaney et al enlarged on Bruce Hollis's seminal work by analyzing five studies in which both the parent compound, cholecalciferol, and 25(OH)D levels were measured. It turn out that the body does not reliably begin storing the parent compound (cholecalciferol) in fat and muscle tissue until 25(OH)D levels get above 50 ng/ml.

The average person starts to store cholecalciferol at 40 ng/ml, but at 50 ng/ml, virtually everyone begins to store it for future use.  That is, at levels below 50 ng/ml, the body is usually using up the vitamin D as fast as you make it or take it, indicating chronic substrate starvation, not a good thing.
  • Hollis BW, Wagner CL, Drezner MK, Binkley NC. Circulating vitamin D3 and 25-hydroxyvitamin D in humans: An important tool to define adequate nutritional vitamin D status. J Steroid Biochem Mol Biol. 2007 Mar;103(3-5):631-4.
  • Heaney RP, Armas LA, Shary JR, Bell NH, Binkley N, Hollis BW. 25-Hydroxylation of vitamin D3: relation to circulating vitamin D3 under various input conditions. Am J Clin Nutr. 2008 Jun;87(6):1738-42.

7. When I asked my doctor for a 25(OH)D blood test, he just laughed and said it was all idiotic.  What can I do?

Help me unleash the dogs of war, the plaintiff attorneys. If you read about past nutritional epidemics caused by society, such as beriberi or pellagra, you will realize that education alone will take decades.

Physicians successfully fought against the idea that thiamine deficiency caused beriberi for decades. However, things are different now. The agents of change in modern America, as obnoxious as they are, are plaintiff attorneys.

Once the first malpractice lawsuits claiming undiagnosed and untreated vitamin D deficiency led to breast cancer, autism, heart disease, etc., get past summary judgment, and they will, and end up in front of a jury, and they will, things will change rapidly.

One of the main reason physicians do what they do is fear of lawsuits. In a matter of months, arrogance and ignorance will give way to 25(OH)D tests and vitamin D supplementation.

  • Goodwin JS, Tangum MR. Battling quackery: attitudes about micronutrient supplements in American academic medicine. Arch Intern Med. 1998 Nov 9;158(20):2187-91.

8. The vitamin D Council takes money from Bio Tech Pharmacal and Lifespan Nutrition and now you are a consultant for Diasorin. With those conflicts, how can I believe what you say?

Believe what you want, most people do anyway.  As far as conflicts, I am actively soliciting them.  No conflicts means no money and I don't want to work in a maximum security hospital for the criminally insane all the rest of my life. (Whoops, I meant a "liberty impaired haven for the mentally challenged who are criminally defiant".)

Furthermore, the Vitamin D Council cannot do what we need to do on $12,000.00 per year (what we get from Bio Tech Pharmacal).  So if you know anyone or any business with some money to donate that would create a conflict, send them our way.

9. My blood test came back at 120 ng/ml.  Am I toxic?

No, vitamin D toxicity has never been reliably documented with 25(OH)D levels less than 200 ng/ml.  Ranges for humans living and working in the sun are between 50 and 100 ng/ml.

John Cannell, MD

The Vitamin D Council

Editor's Note: The Vitamin D Council is a non-profit organization trying to end what Dr. Cannell calls “the epidemic of vitamin D deficiency” (Click to learn more about the Vitamin D Council and Dr. Cannell).

He relies on donations to publish the newsletter and maintain the Council's website. You can subscribe or contribute online on the Vitamin D Council home page. Or, send your tax-deductible contributions to:

The Vitamin D Council

9100 San Gregorio Road

Atascadero, CA 93422