Responding to research indicating that vitamin D may slow the progression of breast, colon and other common cancers, some doctors have begun adding the supplement to their tool kit of cancer therapies alongside more conventional treatments such as radiation, surgery and chemotherapy.
While not all physicians are convinced the evidence is strong enough to warrant taking an extra dollop of the sunshine vitamin, those recommending the course say popping the pills is a simple health strategy that has few, if any, risks and has the added benefit of also improving bone health in those with cancer.
"There is emerging data on breast cancer recurrence rates and vitamin D levels that are quite compelling," says Tracey O'Connor, an oncologist at the Roswell Park Cancer Institute in Buffalo who treats breast cancer and is having her patients take the vitamin.
Giving vitamin D as part of a treatment program for cancer is still relatively new in the medical community, and Roswell Park is one of the first major cancer institutions in North America to have a number of doctors investigating whether wider use of the nutrient may make a difference in the outcome of the disease.
Speaking at a conference this week in Toronto, Dr. O'Connor outlined a protocol she is using for vitamin D in breast-cancer treatment. It involves giving high doses of the supplement to the most deficient patients immediately after they are diagnosed to quickly raise blood levels of the nutrient.
Dr. O'Connor says that having a low level of vitamin D "is quite common" among women with breast cancer, and most patients, typically about 80 per cent, are either deficient or have insufficient amounts.
Current Health Canada dietary recommendations for vitamin D range from 200 to 600 international units a day, depending on age, and were designed to promote bone health and not the far larger amounts being explored for therapeutic possibilities in cancer treatments.
Dr. O'Connor says some breast-cancer patients have such low stores of the nutrient that they need to embark on a crash course of taking up to 50,000 IU a week for several months to bring up their levels. Other patients whose starting levels aren't so poor take a few thousand IU a day. She also monitors blood levels to make sure people don't get too much.
International units are the standard measurement of how much vitamin D is contained in supplements or foods. Multivitamins typically have either 400 or 800 IU, and a cup of fortified milk has 100 IU.
While vitamin D can be taken as a pill, it's also produced naturally in human skin exposed to strong, summertime ultraviolet light, hence it's often given the sunshine vitamin moniker.
In recent years, vitamin D has emerged as one of the most intriguing areas of cancer research. There have been numerous epidemiological studies finding that people with less of the nutrient circulating in their blood are at an elevated risk of developing cancer compared with those who have higher levels. The list of cancers for which this trend has been observed now numbers 18 and includes some of the most common such as colon cancer and breast cancer. Other research has found that those diagnosed with cancer in summer and fall - when blood levels of the vitamin are at seasonal highs because of sun exposure - have longer survival times than people whose cancers are detected in winter and spring.
Although some researchers are fascinated by vitamin D, others are more cautious, in part because previously hyped nutrients, such as beta carotene and vitamin C, were at one time promoted for anti-cancer properties, but subsequent trials didn't confirm any benefits and in some cases even found harm.
Vitamin D also hasn't been subjected to the gold-standard test in medicine, a large-scale, drug-style clinical trial among people who have cancer, to confirm that it slows the progression of the disease.
Pamela Goodwin, an oncologist at Mount Sinai Hospital in Toronto, published research last year indicating there is a possible association between low levels of vitamin D and poor prognoses for those with breast cancer. Women with low levels had an increased risk of recurrence and lower overall survival rates.
But Dr. Goodwin cautioned that such research doesn't prove that vitamin D caused the outcomes she observed.
"We don't have sufficient information yet to conclude that there is a causal association between vitamin D and recurrence," she said. "The jury is still out."
She does recommend having adequate levels of vitamin D for overall good health and said people can achieve this with supplementation of less than 1,000 IU a day.