what they said (Hover the mouse cursor over underlined words for more info)

Ingesting about three times as much vitamin D as the norm may lower an individual's risk of developing colon, breast or ovarian cancer, a study says.

North Americans typically ingest 320 units a day of the vitamin, consisting of 200 from food and 120 from supplements. Daily intake of about 1,000 units may cut the odds of getting colon cancer by about half, and the chances of getting breast or ovarian cancer by about a third, according to the researchers.

Vitamin D supplements could reduce cancer incidence and mortality "at low cost, with few or no adverse side effects," the researchers said in an article appearing in the February 2006 issue of the American Journal of Public Health.

The original article can be found at: http://www.canada.com/vancouversun/news/story.html?id=6068538a-3638-4be7-a85c-bd489a798d46&k=19079

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what we said (Hover the mouse cursor over underlined words for more info)

This story on the health benefits of vitamin D is drawn from a meta-analysis of studies examining the impact of this important vitamin on colorectal, breast and ovarian cancer. The story's major flaws concern the lack of detail on the evidence on which the health claims are made, the inappropriate use of relative numbers and insufficient detail on the potential side effects or adverse effects that may be associated with too much vitamin D.

In terms of benefits, the article unfortunately only reports relative numbers noting that "1,000 daily units may cut the odds of getting colon cancer by about half, and the chances of getting breast or ovarian cancer by about a third". These benefits of "a third" or "a half" are meaningless numbers without context. Unless a person has an understanding of what their baseline risks of developing these diseases are, these relative numbers make little sense. In other words, if your risk of developing colon cancer is 2 in a million, and can be reduced, by vitamin D supplementation to 1 in a million that is a 50% reduction. The two ways to describe that risk reduction is a 50% relative risk reduction or a "1 in a million" ( 0.000001%) absolute risk reduction.

It appears that the journalist did not journey too far from the press release issued by the University of San Diego, and failed to secure any comments from researchers outside the study.

It was good to see that costs of a daily supplement, and alternative sources (various foods, and sunlight) of Vitamin D are mentioned. There is a large body of evidence suggesting Vitamin D possesses cancer-preventative properties, yet a better understanding of the strength of that evidence would provide the reader with better insights into whether or not they need to purchase a daily supplement of Vitamin D.

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