Page 26 - Spring2009

POTENTIAL DANGERS OF VITAMIN D

Dr, John Cannell of the Vitamin D Council argues that humans do not begin storing vitamin D in fat and muscle tis-
sue until blood levels of 25-hydroxyvitamin D (also known as calcidiol and abbreviated 25(OH)D) reach 50 nanograms
per milliliter (ng/mL) and that below this amount the enzyme that converts vitamin D to calcidiol for storage in the blood
1
suffers from chronic “starvation.” On his Vitamin D Council web site, Cannell now recommends blood levels of calcidiol
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between 50 and 80 ng/mL and supplementation of 1,000 IU for every 25 pounds of bodyweight. For someone weighing
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between 150 and 175 pounds, he thus recommends between 6,000 and 7,000 IU per day from all sources. Cannell and
his co-authors consider vitamin D to be perfectly safe for most people in amounts up to 10,000 IU per day—even while
1
simultaneously recommending people avoid supplementing with vitamin A. In reality, however, these amounts of vitamin
D could be dangerous when combined with low intakes of vitamins A and K as occurs in the general population.
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Cannell and colleagues cite two studies in their journal article justifying the statement that storage of vitamin D begins
at 50 ng/mL. 54,55 The first of these was a preliminary report published in 2007, while the second was a much more thorough
and consequently more accurate report published in 2008. The final report concluded that vitamin D is completely
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converted to calcidiol when serum calcidiol levels are below 35 ng/mL and inputs from diet and sunshine combined are
below 2000 IU per day. Above these levels, the conversion of vitamin D to calcidiol drops to an average of 43 percent
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and much of the remaining vitamin D is stored in body tissues, most likely in adipose tissue. The vitamin D appears to be
released from storage as blood levels of calcidiol decline. The authors observed that other studies have shown calcium
absorption to be maximized and serum parathyroid hormone (PTH, a promoter of bone resorption) to be maximally sup-
pressed at calcidiol levels of 30-34 ng/mL, in close agreement with their own study.
In support of the contention that daily vitamin D intakes of up to 10,000 IU are perfectly safe for most people, Cannell
and colleagues cite a risk assessment published in 2007 that used abnormally high blood and urine calcium levels as its
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indicator of potential toxicity. Clinical vitamin D toxicity, according to these authors, occurs when calcidiol levels exceed
600 ng/mL and is accompanied by pain, conjunctivitis, anorexia, fever, chills, thirst, vomiting and weight loss. If clinical
vitamin D toxicity is the only concern, 10,000 IU of vitamin D per day is likely to be harmless. Evidence suggests, however,
that vitamin D can begin causing less acute adverse effects at much lower levels when intakes of vitamins A and K are
2
inadequate. This is of especial concern because over one quarter of Americans already consume less than half the RDA
for vitamin A, and blood markers for inadequate vitamin K status are universally present in the general population. 58
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2
A recent double-blind, placebo-controlled study found that 400 IU of vitamin D and 1,000 mg of calcium increased
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the risk of kidney stones by 17 percent. As described on page 21 of the main text, the vitamin D may have contributed
to stone formation by increasing the demand for vitamin A in an elderly population counseled to avoid intakes of vitamin
A above the RDA. A 2001 study found that males in South India with calcidiol levels over 89 ng/mL had three times the
risk of heart disease as those with lower calcidiol levels. Vitamin D increases the demand for vitamin K as well as vitamin
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2
A, and deficiency of vitamin K contributes to calcification of all of the soft tissues, including the kidneys, causing kidney
2
stones, and the arteries and aortic valves, leading to heart disease. 60,61 If the association between calcidiol levels and heart
disease represents true causation, which it certainly could, it suggests that calcidiol levels begin contributing to soft tissue
calcification at levels much lower than 89 ng/mL, at least in the absence of adequate levels of its partner vitamins, A and
K .
2
In the third National Health and Nutrition Examination Survey, calcidiol levels of 35 ng/mL were associated with high
bone mineral density (BMD) among all ages and races. In adults over 50, however, the association above this point was
remarkably inconsistent. In whites, it kept increasing until 50 ng/mL and leveled off thereafter. In Mexican Americans,
it began declining after about 40 ng/mL. In blacks, BMD began declining after 35 ng/mL and sharply declining after 50
ng/mL. Whether these differences are due to genetics, differential intakes of other fat-soluble vitamins, differential use of
anticoagulants or other drugs that interact with fat-soluble vitamin metabolism, or other unknown factors, we do not know.
At this stage of the game, however, it makes much more sense to emphasize the importance of obtaining calcidiol levels
between 30 and 40 ng/mL, levels where we have the most solid evidence of benefit and the least indication of harm.
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Average blood levels of calcidiol in people with abundant exposure to sunshine range from 40 to 65 ng/mL. These
levels are most likely perfectly safe when intakes of vitamins A and K from organ meats and animal fats are just as abundant
2
as the sunshine. The research cited above, moreover, suggests that vitamin D would be stored in adipose tissue at these
levels and released when calcidiol levels drop, as they would during the winter in temperate climates—an added bonus for
those who wish to obtain their vitamin D from foods like cod liver oil and fatty fish rather than from supplements during
the winter. People with dark skin, however, should be careful to make sure that their calcidiol levels stay above 35 ng/mL
year-round and use a supplement if necessary. Maintaining levels of 50-80 ng/mL, on the other hand, might be not only
unnecessary, but dangerous in the context of a standard diet deficient in the other fat-soluble vitamins.

24 Wise Traditions SPRING 2009