I previously posted about a clinical trial which proved that 1100 IU daily of vitamin D - about triple the recommended amount - can reduce cancer by 77%. Unfortunately, the trial did not test vitamin D in the absence of supplemental calcium, did not test men, and did not test people under 50, so we only know that this works for older women who also take calcium supplements.
There were two things that were interesting about this 2007 result.
The first is that it was a trial - a double blind controlled experiment - and not just a epidemiological study. What's the difference? A study involves gathering data on what people do or have already done and analyzing the data statistically. An experimental trial involves randomly assigning people in advance to a control group or an intervention group and giving the intervention group a drug - or in this case a supplement - and the control group a placebo.
One sees the results from a new epidemiological study on cancer every week or two. This is because it's easy to do a study: there's a lot of data that has already been gathered, and all one has to do is go analyze it in a new way. Unfortunately, studies cannot prove a causal relationship. The best they can show is a correlation. For example, one recent study showed a correlation between eating chocolate and being thin - but we don't know whether that was because eating chocolate causes one to stay thin, because being thin means one feels more free to eat chocolate, or because of some other issue - perhaps more affluent people are both more likely to stay thin and more likely to eat chocolate, even though the two behaviors are otherwise unrelated. There have been some notable cases where the implied causation from study results turns out to be exactly wrong - for example use of hormone replacement therapy to prevent osteoporosis in older women, which showed promise in studies, but later turned out actually to exacerbate the problem.
Controlled trials are much rarer, because it's more difficult to recruit people in advance, and you have to get them to take the medicine - or the placebo - and not just get them to fill out questionnaires. However, controlled trials can actually prove a causal relationship. Since the only difference between the control and experimental groups is whether they take the medicine, you know that, if there's a clear difference in the results, the medicine was the cause of the result, and not just something that happened to correlate to the result. In this case, the trial reported in the 2007 paper actually proved that 1100 IU of extra vitamin D, combined with 1400-1500 mg of extra calcium, prevented over three quarters of cancers in older women.
The second interesting thing about this result was that it took so long to happen. It has been known for more than half a century that cancer rates are higher at higher latitudes, and suspected for as long that the reason was because people at higher latitudes get less sun and thus less vitamin D. Unfortunately, since there's not much money to be had selling a supplement that isn't protected by a patent, no one had bothered to do a clinical trial on the subject - even this result was a side effect of testing the combination of vitamin D and calcium on osteoporosis, with the examination of the cancer result basically an afterthought rather than the purpose of the experiment.
That obviously says something about our health care system. The economic and governmental incentives are set up so that lots of money is spent testing expensive patented ways to cure cancer, but very little on testing inexpensive unpatented ways to prevent cancer, by either private industry or the government. So there was some question whether, even after this 2007 result, anyone would bother to do a trial testing the effects of just vitamin D, without calcium, on men as well as women, and on people under 50 as well as people over 50.
That's why I was pleased to receive a recent letter asking if I would like to participate in a trial testing some of these effects. The new trial will test men over 50 as well as older women, and will test vitamin D in the absence of calcium. It will also test fish oil and the combination of fish oil and vitamin D. It's a 5 year trial, so some time towards the end of the decade we should have a pretty definitive answer on whether vitamin D prevents cancer in older men, and whether it prevents cancer in older women even without extra calcium.
Unfortunately, I had to decline to participate; I'm already taking a vitamin D supplement, and participation in the new study requires that one not take supplemental vitamin D outside of the study medications. I like furthering the cause of science, but not so much that I'm willing to give up something that is likely protecting me from cancer. I'm still glad the study is happening, though.
2007 paper showing that 1100 IU of vitamin D plus 1500 mg of calcium reduces cancer incidence in postmenopausal women by 77% starting after a year:
New study on whether vitamin D or fish oil reduces cancer in men over 50 and women over 55, currently recruiting participants:
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Wow, vitamin D and cancer. That is amazing. Thank you so much for the info. I'm going to take some vitamin D right now. I have been trying to recoup from an illness and i know i should take more vitamins, i just get too lazy. Thanks for your informative blog.