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Vitamin D: A dosing down?

Posted on behalf of Tiffany O’Callaghan

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A new report concludes that huge doses of the vitamin D are unwarranted and may even be harmful, and it suggests that most Americans and Canadians aren’t suffering from a deficiency in the “sunshine vitamin”. The Institute of Medicine (IOM) report analyzed findings from more than 1,000 studies of vitamin D and calcium intake.

In recent years, there have been a flurry of studies examining the potential benefits of vitamin D for everything from helping equip the immune system to fight infections to potentially inhibiting the growth of cancerous cells. Yet all this research has failed to indicate just how much vitamin D is needed to stave off deficiency. The last recommendations from the IOM released in 1997 suggested that, depending on age, 200 to 600 international units (IUs) of vitamin D was an “adequate intake” to maintain health.

Yet, as the Associated Press points out, as more studies have emerged suggesting protective benefits, some advocates have recommended that people consume amounts as high as 2,000 IUs per day, and many supplements are now sold in doses of 1,000 IUs.


The new report goes beyond the earlier adequate intake recommendations to establish dietary reference guidelines that are nowhere near those high levels. According to the report, people under age 70 need no more than 600 IUs of vitamin D per day, while seniors may require up to 800 IUs to maintain bone health.

Why the discrepancies? The report authors believe that inconsistency in blood tests — and in the cut off points used to determine deficiency — may have contributed to inconsistencies in recommendations as well as inflated numbers of people with D deficiency. (As they point out, whether or not someone was deemed deficient could have hinged on which lab processed the blood test.) In fact, according to the report, an analysis of vitamin D levels in national blood samples found that the majority of Americans and Canadians are getting plenty of both vitamin D and calcium.

Regarding further benefits of vitamin D — for cancer prevention or for treating diabetes, as some studies have suggested — the IOM committee pointed to inconsistent and conflicting results and found that there was not yet enough rigorous evidence to suggest a substantial benefit beyond the amount needed to maintain healthy bones.

Of course, with so many hopes hinging on vitamin D, these new recommendations certainly won’t put the subject to rest. Yet, until there is more definitive science beyond the benefits to bone health, the IOM committee recommends proceeding with caution. After all, as committee chair and nutrition expert A. Catharine Ross said in a statement about the findings: “Past cases such as hormone replacement therapy and high doses of beta carotene remind us that some therapies that seemed to show promise for treating or preventing health problems ultimately did not work out and even caused harm. This is why it is appropriate to approach emerging evidence about an intervention cautiously, but with an open mind.”

Image: photo by Perfect Insecto http://www.flickr.com/photos/perfectoinsecto/4291561083/] via Flickr under Creative Commons

Comments

  1. Report this comment

    Tom said:

    Get that blood test to see if you need Vitamin D supplements (http://amzn.to/f7QlX1). Too much is Toxic. Too much calcium and Vit D can cause kidney stones.

  2. Report this comment

    Pete said:

    There is no evidence that vitamin d in the form we are considering here causes kidney stones, they form when doctors start giving people active vitamin d and disrupt the bodies ability to control calcium levels. You cannot get active vitamin d without a doctor’s prescription.

    Too much vitamin d is toxic but it sets in after about 6 months of 40,000IU a day.

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    Saibal Mitra said:

    I don’t think that you would be able to get to the recommended diet regarding fruits vegerables meat etc. etc. using the same logic as used w.r.t. vitamin D. E.g., where is the hard evidence that eating two pieces a fruit per day, keeps cancer away?

    Instead, one should look at nutrion, vitamins etc. from the perspective of optimal body function and take into account the fact that evolution must have led to an optimal outcome. Then, if we taking this perspective on vitamin D, a very relevant fact is that vitamin D is not going to be produced unless the Sun is not high in the sky. Since vitamin D acts as a hormone in the body, switching on genes etc., this must have been a deliberate choice.

    So, one has to ask why you would want to let the body function differently if the Sun doesn’t rise high in the sky anymore. An obvious answer could be that it is advantageous to save energy before the arrival of Winter. One can imgine that in Fall when the Sun doesn’t rise high in the sky anymore, the drop in vitamin D levels is used to modulate the immune function. Then this may come at the risk of a higher chance of getting cancer, however, it will help the animal to build up more fat reserves to make it through winter.

    Also the less fat reserves an animal has to begin with, the sooner vitamin D levels will start to fall (vitamin D is stored ion body fat), so it will start to start saving energy sooner.

    Now, the lower vitamin D levels get the more energy saviong measures will be taken. Getting calcium from food is not free of charge. The concentration of calcium in food isn’t particularly high and there is a cheap alternative available: getting it from the bones where the concentration of calcium is much higher.

    Balancing the benefits of maintaining the skeleton and getting more energy to make it through winter, one can imagine that at the end of Winter, it may be advantageous to forego maintaining the bones for a few weeks to save energy when digesting food that is now in very short supply.

    So, if this picture is correct, the vitamin D level at which the bones are on the threshold of being properly maintained, should be considered to be extremely low levels and one should really focus on the vitamin D levels people get when they spend a lot of time outdoors when the Sun is high in the sky as healthy vitamin D levels.

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