Updated Dec 1, 2010, just after the Institue of Medicine pronouncement
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My Vitamin D Opinion
I titled this section with the words "my opinion" because I want to make it absolutely clear that I am giving my opinion. I am a nutritionist, dietitian, and epidemiologist with experience in cancer research, so I feel that I have something to offer on this topic. But always, talk to your doctor if you have any questions about what is right for you with dietary supplements, including vitamin D.
I believe that 600 IU/day recommendation for most adults is set too low. I don't believe that the 10,000 IU/day of vitamin D suggested by advocates of high dose vitamin D are necessary. I think this is overkill for most people and as we've learned with a lot of dietary supplements, more is not necessarily better. Sometimes higher doses of vitamins turn out to cause more harm than good in the long run.
I believe that the recommendation that most people need 1,000 to 2,000 IU per day of vitamin D will be vindicated in the long run. I also believe that most people do not get enough vitamin D from diet alone.
One interesting clinical trial out of Japan really caught my interest and I wish that the IOM panel had given it more weight. The study, which was the gold standard, double-blind, randomized, placebo-controlled trial, found that giving 1,200 IU/day of vitamin D to school kids (around 10 years of age) reduced the risk of flu (influenza A) by 64%. Risk of asthma attacks was reduced by 83% in the group receiving supplements.