Canada and the United States could cut their annual incidence of colon and breast cancer, two of the most common and deadly malignancies, by about 25 per cent if everyone took vitamin D supplements of 2,000 International Units a day, according to a new study.
The recommended dose - which corresponds to the maximum safe level set by Health Canada - comes from a team of researchers at the Moores Cancer Center at the University of California, San Diego, who said in the study that they believe there are "no unreasonable risks" from taking that amount.
Increasing vitamin D intake is "a strong means of prevention," said Cedric Garland, a professor of family and preventive medicine and lead author of the study, which appears today in the Annals of Epidemiology.
He also said that those who already have the cancers could improve their odds of beating the diseases by taking vitamin D as they undergo chemotherapy and radiation treatments, or while dealing with metastases.
"I think it offers the hope of pulling back from the extremely toxic doses of chemotherapy that we think we need right now, and ultimately I think it offers a way of reducing cancer death," he said.
The call by a leading U.S. team researching vitamin D to pop more of the sunshine vitamin comes as the nutrient is emerging as one of the most debated topics in cancer prevention and treatment.
Medical findings that some cancers and other chronic diseases may be linked to having too little of it have become so frequent that the Canadian and U.S. governments have ordered an expert panel to assess whether current intake advice needs to be revised.
The panel is expected to complete its work next year, and in the meantime the governments say people need take only 200 to 600 IU a day, depending on age. This recommendation, set in 1997, is based on bone health and isn't linked to any of the purported anti-cancer benefits.
The new study is one of the most detailed to date to look at the association between blood levels of Vitamin D and the odds of developing colon or breast cancer in the future.
When doctors have conducted these kinds of blood surveys, and followed up years later to see who developed the cancers, they've noticed a striking pattern: Those with the most vitamin D generally have about half the risk of those with the least.
The University of California researchers estimated how much the two cancer rates would fall if everyone raised their blood levels by taking 2,000 IU a day, or the amount in two of the highest-dose supplement pills allowed on the Canadian market.
They selected the 2,000 figure because it's the current government maximum for those not under doctor's care, but Dr. Garland said further research might lead to a higher figure.
The dosage exceeds the 1,000 IU a day recommendation issued in 2007 by the Canadian Cancer Society, the first major public-health group in the world to call for taking the vitamin to cut cancer risk.
The cancer society said non-whites should take 1,000 IU a day year-round, and whites during fall and winter, when a lack of sunlight makes it impossible to make the vitamin the natural way.Not all medical experts are jumping on the vitamin D bandwagon.
The International Agency for Research on Cancer, a United Nations affiliate, called last year for a major drug-style trial to prove the safety and efficacy of vitamin D before health authorities recommend population-wide dosing. Such a trial would likely cost more than $100-million (U.S.) and take years to complete.
The IARC cautioned that high vitamin D levels in blood samples may have little to do with lowering cancer risk, and might just be a sign that people have a healthy lifestyle involving summer exercise and sun exposure.
