Vitamin D: What’s the Right Amount?

To take more than 1000 IU/day or not, that is the question. How much should we be taking? Recently, some Vitamin D research was released suggesting that Canada’s (and the USA’s) current vitamin D recommendations are too low due to some statistical errors that were made when calculating the RDA for vitamin D. If this is true, it could have serious implications for the health status and disease risk of Canadians.

After reviewing the evidence and the error claims put forth, the IOM (Institute of Medicine in the US) and Health Canada concluded that no error was made in the statistical calculation of recommended vitamin D intake. Some fear that increasing vitamin D recommendations would cause more harm than good, but the evidence doesn’t seem to support this notion, at least up to 10,000 IU/day for most people.

One study found that in adults taking 1000 IU/day of vitamin D3 for 11 weeks, their 25(OH)D values increased but their 1,25-dihydroxyvitamin D values didn’t change. This is partly what prompted the Edmonton-based researchers to question the current RDA’s in the first place. 25(OH)D is apparently the most accurate marker of vitamin D status, but it must then be converted into 1,25-dihydroxyvitamin D, the active form of vitamin D. It is generally accepted that blood levels of 25(OH)D should be between 30-50 ng/mL, and that anything less than 30 ng/mL is likely insufficient and any more than 50 ng/mL could be detrimental to some but not all.

The only FDA-approved pharmaceutical form of vitamin D is vitamin D2, not D3. D2 enters the bloodstream but is not converted as efficiently into D3 and therefore 1,25-dihydroxyvitamin D. Toxicity usually occurs at extremely high doses (ie. 50,000-100,000 IU/day), and these high doses are usually the result of physician-directed treatment with vitamin D2. Vitamin D toxicity can indeed cause hypercalcemia in adults, and these effects are even more pronounced in infants. However, researchers speculate that documented cases of vitamin D toxicity in infants that occurred at low doses (1000-1500 IU/day) in the past were probably the result of an underlying disease (ie. William syndrome or a vitamin D hypersensitivity disorder).

While Health Canada allows up to 1000 IU/day for people of all ages to be given in supplement form, the Canadian RDA is still just 600-800 IU/day for adults. Osteoporosis Canada recommends that older adults or adults at high risk take up to 2000 IU/day. In the US, the FDA just increased their RDA for Vitamin D from 400 IU/day to 600 IU/day.
4,000 IU/day is Health Canada’s safe upper limit, and the IOM’s upper limit for adults and teens in the US is 10,000 IU/day. This at least gives some latitude for health care practitioners and the public to make informed decisions about their health needs and vitamin D requirements.

Public nutrient recommendations tend to be more on the conservative side for good reason, and this is due to the need for responsible decisions that affect an entire population with varying body chemistry and needs. There are always exceptions where certain people cannot tolerate a higher dosage recommendation (for example, people with a vitamin D hypersensitivity), and there are always those who require more to reap full benefit (for example, dark-skinned pregnant women). In addition, people of varying race and age may have different requirements (for example, older adults and darker skinned people do not synthesize vitamin D in the skin from sun exposure as easily as younger, lighter skinned people). Therefore, the Canadian Council of Food and Nutrition recommends that public health practitioners familiarize themselves with the current research when working with clients on dosing recommendations. This ensures that each person is being recommended the accurate dose for their specific needs. A one size fits all approach to supplementing and medicine is never the best approach, although unfortunately this is the way we tend to function. Therefore, it is important to note that while Health Canada’s recommendations are probably lower than necessary for most Canadians, they must exercise their responsibility to protect the masses. It is therefore up to health care practitioners to educate their clients and for consumers to seek education and nutritional counseling around the dietary needs for themselves and their families.

So while Health Canada and the IOM have not increased their vitamin D RDA to the proposed 6000 or 7000 IU/day as suggested, the tolerable upper limit rests at 4000 IU/day for adults in Canada. Excessive amounts of a good thing are not always a good thing, so use wisdom and consider your individual situation when deciding how much more vitamin D to take than the standard 1000 IU/day.


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