Nevertheless, the idea that vitamin D insufficiency plays a role in cancer and other chronic adult diseases continues to gain scientific credence as a plausible theory, earned new respect for the long-underappreciated vitamin.
Though it first drew attention in the 1920s as a cure for rickets (bone health, not cancer, is why Health Canada even has a recommended intake), it has largely been treated like Rodney Dangerfield ever since. In our health-conscious age, it has been overshadowed by supplements such as vitamin C and beta carotene.
But since the Garland brothers kicked off interest in vitamin D with their data on colon cancer, other studies have shown that more than a dozen other cancers, including the big killers, breast and prostate, as well as an array of other diseases appear sensitive to insufficiencies of the vitamin.
The idea behind the research is simple: Humans evolved in a sunlight-filled environment near the equator, and still have countless biological processes exquisitely calibrated to the rich vitamin D levels we would have if we were still basking under the hot sun year-round.
But by migrating to higher latitudes, where strong sunlight is not present during the fall and winter, most humans upset their vitamin D metabolism, creating susceptibilities to chronic ailments that research is now linking to insufficiencies.
The question for Canadians is: If we're so short of a crucial vitamin, shouldn't we be compensating? And if we did, would vitamin D be a proverbial magic pill, capable of curing much of what ails us?
Although the guidelines jointly issued by the U.S. and Canadian governments say adults need only 200 to 600 IU of vitamin D daily, depending on age, the women in Dr. Heaney's study took 1,100 IU daily, while he himself takes 1,500 IU daily.
(Although the international units nomenclature makes the numbers seem large, the actual weight represented by a single IU of vitamin D is dust-like, at less than a millionth of a gram. The vitamin, by acting like a hormone in the body's cells, packs a big biological punch in minute amounts.)
The Canadian Cancer Society is one of the more conservative health-advocacy agencies, but last year became the first major organization in the world to embrace the idea of large-scale, population-wide vitamin D supplementation to combat cancer. It started recommending that white adults take up to 1,000 IU daily in fall and winter, and non-whites, because of their higher susceptibility to vitamin D insufficiency at northern latitudes, take that amount year-round. (Canada doesn't keep national illness statistics by race, so the degree to which non-whites are being affected by ailments linked to low vitamin D levels isn't known.)
The Canadian Pediatric Society followed suit shortly after, calling for pregnant and breastfeeding women to take 2,000 IU daily, with a goal of preventing childhood diseases.
The Canadian Cancer Society's decision came after years of monitoring the research. Vitamin D "kept coming up. It kept hitting the bar that reaches your attention," says Heather Logan, the society's director of cancer-control policy.
"It wasn't one study and that was the end of the story. There were multiple research studies continued to be published in peer-reviewed journals."
One study, in the journal Circulation, found that those with low vitamin D status had a 62-per-cent increased risk of heart failure. Another, published in Archives of Internal Medicine, found that those who take vitamin D supplements cut mortality risk by 7 per cent. A third report, by scientists at the U.S. National Cancer Institute, found that, while vitamin D didn't affect overall cancer-death risk, those with relatively high levels of it in their blood had a 72-per-cent lower risk of dying from colorectal cancer.
Other studies have found that low blood levels are an excellent predictor of who goes on to develop cancer and heart disease and that people diagnosed with cancer during the vitamin D-rich summer have a better prognosis than those diagnosed during winter.
Not everyone is convinced, however. Critics charge that most of the findings - such as the Garlands' cancer maps - constitute only circumstantial evidence. And when the Canadian Cancer Society asked the American Cancer Society to join them in recommending more vitamin D, it refused.
"I think it's fair to say we had discussions and we agreed to disagree on that. Our position is that we really want what I call solid evidence ... that there in fact is a reduction in cancer mortality without a significant increase in risk with vitamin D supplementation," Dr. Lichtenfeld says. He wants to see drug-style clinical trials to validate the benefits and assess the risks, he says, before telling 330 million Americans to start taking supplements.
Similarly, John McLaughlin, vice-president of preventive oncology for Cancer Care Ontario, says the research on vitamin D is too thin at this point to recommend taking higher doses to prevent cancer. He dismisses Dr. Heaney's study as "largely uninformative" because of its small size (about 450 women) and because the subjects also took calcium supplements, which may have affected the results.