The Use and Safety of Vitamin D

The use and safety of Vitamin D

The North American official safe upper limits for vitamin D daily intake (D.R.I. ‘97) are:

Infants 0–12 months, 1,000 IU (25 mcg)

Males and females 1 year and older, 2,000 IU (50 mcg)

Pregnant and nursing women, 2,000 IU (50 mcg)

These safe upper limits are not based on any coherent body of evidence, and are currently under review. Linda Meyers, then-director of the Food and Nutrition Board which sets the government's recommended daily intake values for all vitamins and some minerals, stated in 2002 that it was time to look at intake standards again for vitamin D with a view to setting higher limits.

In December ‘04, the F & N board began discussions with nutrition experts on which nutrients needed to be re-evaluated. In the context of widespread hypo-vitaminosis D (vitamin D depletion), a form of malnutrition contributing to the current epidemic of osteoporosis, Vitamin D was put in the first group to be re-examined.

This decision was heavily influenced by two critical papers by Dr Reinhold Veith on vitamin D’s safety and therapeutic index (Vieth ’99, Vieth et al ‘01), and by the simple fact that for most skin types, a full body minimal erythemal dose of UVB light - (ie mowing the lawn on a summer’s day with your shirt off until your skin gets faintly pink) - results in the skin producing about 20,000 units of Vitamin D3 (Holick ’81, Holick ’95). This is 10 times more than the current RDA! Indeed, normal rates of endogenous D synthesis prove that our current RDA values are gravely inaccurate.

It is noteworthy that Ian Munro, the chair of the relevant Institute of Medicine (IOM) committee which sets vitamin levels, wrote a letter to the Journal in which he complimented Vieth’s paper and promised that Veith’s findings would be considered in a future IoM review (Munro ‘01).

Additional data regarding the true safe upper limit of D can be derived from clinical studies in which high doses of vitamin D were used therapeutically, and without toxicity. For example, hyperparathyroidism is successfully managed with 50,000 to 200,000 IU of vitamin D daily (Woodhead et al ‘80), while rickets generally requires a dose of 1,600 IU/day, and may require a daily dosage of 50,000 to as much as 300,000 IU in resistant cases (Eguchi & Kaibara ‘80).

In one of the best documented clinical cases of D toxicity, a man who took 156,000 to 2,604,000 IU of cholecalciferol a day for two years recovered uneventfully after the proper diagnosis, and treatment with steroids and sunscreen (Koutkia et al ‘01). This case actually demonstrates the very high therapeutic index of vitamin D, as the dose ingested over the two-year period is as much as 13,000 times the RDA!

Vitamin D should be used cautiously in certain medical conditions including primary hyperparathyroidism, sarcoidosis, tuberculosis, kidney disease and lymphoma. People with these conditions may develop hypercalcemia in response to increased in vitamin D intake and should consult a qualified health care provider before taking vitamin D supplements. Patients taking digitalis, calcium channel-blockers or thiazide diuretics should have physician supervision before and while taking extra vitamin D.

Nevertheless, we should keep the vitamin D story in perspective. Vitamin D experts are unanimous: the real health problems related to vitamin D are to do with hypo-vitaminosis D.

In temperate zones such as middle and northern Europe, the majority of people do not get enough vitamin D from their diet or from sunshine, and are likely to suffer ill health as a result. The classical vitamin D-deficiency diseases are rickets and osteomalacia, but a surprising number of other conditions have also been linked to a lack of D. These diseases, which show a marked increase the further you live from the equator, include osteoporosis, cancers of the prostate, breast and colon (Garland et al ’85, Glinghammar et al ’97, La Vecchia et al ’97, Langman & Boyle ’98, Martinez & Willett ’98, Blutt & Weigel ‘99, Holt ’99, John et al ‘99), and auto-immune diseases such as Type 1 diabetes, rheumatoid arthritis and multiple sclerosis (as cited in Vioflex section, above). Genetic risk factors for all these diseases are known, and it is no coincidence that many of the risk-denoting genes reduce the body’s ability to utilise vitamin D!

As described in my web site , vitamin D appears to protect against auto-immune conditions by modifying the immune system in a way that damps down tissue-damaging auto-immune reactions. Vitamin D’s anti-cancer mechanism probably includes the induction of re-differentation and apoptosis, combined with anti-angiogenesis (Shokravi et al ’95, Studzinski & Moore ’96, Holt et al ’02, Holick ‘04).

How much Vitamin D should we take?

The US Institute of Medicine of the National Academy of Science admit that they do not yet know what the recommended daily allowance (RDA) of vitamin D should be. Instead, they have suggested an AI (or Adequate Intake) level, which represents the daily vitamin D intake that should maintain bone health and normal calcium metabolism in healthy people (I.O.M. ’99). That’s a major problem ... because the level of D needed to maintain bone health appears to be considerably lower than the dose needed to reduce the risks of cancer and autoimmune disease.

In the lack of any governmental consensus I would at this time back Reinhold Veith and suggest 4000 IU’s (or 100 mcg) of vitamin D / day as an optimal and safe protective dose. Remember, this is less than half the amount of vitamin D that you would produce by sunbathing for half an hour! In fact, the main reason why recommended D intakes are so low is that they were drawn up by nutritionists who were obsessed with diet, and had forgotten what a small contribution dietary D was ‘designed’ to make.

As there are very few natural foods that contain significant amounts of vitamin D, it is quite obvious that we were ‘designed’ to obtain most of our vitamin D through sunlight. In this sense D is not a vitamin at all; the definition of a vitamin is a substance we cannot make for ourselves, but must obtain in small amounts in our diet. However, people living at latitudes where exposure to sunlight is limited during the winter months, and anyone who does not have the inclination or the opportunity to spend time in the sun can easily become depleted or deficient in vitamin D, and would do well to supplement.

Vitamin D supplements are important at any age but they are even more so in the elderly. Older skin is less effective at synthesising vitamin D, and older kidneys are less able to convert vitamin D into its final, active form. (MacLaughlin & Holick ’85, Holick et al ’89, Need et al ’93, Lips ’01). Other groups particularly vulnerable to D depletion include those with darker skins (Harris et al 2000, Nesby-Dell et al ‘02), those living outside the tropics and sub-tropics (Webb et al ’88), those who have little exposure to sunlight (ie house-bound, shift-workers etc) (Webb et al ’90, Fairfield & Fletcher ‘02), and anyone with fat malabsorption conditions such as Crohn’s Disease or celiac disease (Lo et al ‘85).

It is likely, therefore, that all these groups have an increased risk of D-depletion disease, including osteoporosis and the cancers and auto-immune disorders listed above. They can either wait for an illness to develop before offering themselves up to the pharmaceutical-medical establishment; or they can take steps to improve their nutritional status, and look after their own health.

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