Low vitamin D heightens breast-cancer mortality rate
Disease twice as likely to spread in women deficient in the nutrient, study finds
Women diagnosed with breast cancer are nearly twice as likely to have the disease spread to other parts of their bodies and are 73 per cent more likely to die from it if they have low levels of vitamin D, according to a Canadian study.
The research is being heralded as significant because it raises the possibility of treating breast cancer using an everyday nutrient that is widely available over the counter for only pennies a day. It also suggests that doctors may one day routinely check the vitamin D status of their patients and correct low levels through supplementation to improve their odds of beating the cancer.
The findings, released yesterday by the American Society of Clinical Oncology, are the first time researchers have been able to link not having enough of the sunshine vitamin to the progression of breast cancer and the fate of those with the dreaded disease.
The study is of particular importance to women in Canada, where vitamin D insufficiency is endemic because the country’s weak winter sunlight isn’t strong enough for nearly half the year to create the nutrient the natural way, through the action of strong ultraviolet light on skin.
Only one in four women in the study had adequate amounts. Surprisingly, younger women tended to have the lowest levels because they generally didn’t use vitamin D supplements, which older women often take to prevent bone fractures.
“Vitamin D deficiency is common,” observed Pamela Goodwin, senior investigator at Mount Sinai Hospital’s Samuel Lunenfeld Research Institute in Toronto and principal researcher on the study. “It’s associated with high-grade tumours, and in our data set, it’s associated with an increased risk of [cancer spread] and death.”
Other researchers said the finding is putting vitamin D in the spotlight.
“The whole vitamin D story is important,” says Larry Norton, a medical oncologist at the Memorial Sloan-Kettering Cancer Center in New York and scientific adviser to the Breast Cancer Research Foundation, which financed the study. He said vitamin D is “critical for general health,” including people with cancer.
The American Society of Clinical Oncology, one of the world’s major organizations for cancer doctors, considered the Canadian study to be among the most important to be discussed at its coming annual meeting, where it will be formally presented later this month.
The study was conducted at three Toronto hospitals affiliated with the University of Toronto, and followed for more than a decade the lives and deaths of 512 women diagnosed with breast cancer between 1989 and 1995. All the women gave a blood sample before their cancer treatments started, from which their vitamin D status was determined. All had cancer at early stages that had not spread to other organs, and had an average age of 50.
Researchers were interested in looking at vitamin D because breast-cancer cells have receptors able to use it. These receptors influence an estimated 30 to 40 genes that, among other functions, play a role in cell reproduction, a crucial factor in the out-of-control growth characterized by cancer.
Although this new research indicates that poor vitamin D status raises the risk of death from breast cancer, Dr. Goodwin said scientists haven’t yet determined through clinical trials the optimum amount to be taken in supplement form for the best odds of fighting the disease, and she cautioned that cancer patients shouldn’t react to her findings by taking big doses.
That is because the research also raised the possibility that vitamin D is something of a Goldilocks nutrient: having too little or too much isn’t desirable, and the optimum may lie somewhere between the extremes.
What gave researchers pause was that among the 106 women who died during the 11-year study period were a small number with relatively high vitamin D levels, although there were so few of them that the results weren’t statistically significant and could have been due to chance.
The group of women in the study with the lowest rate of death had levels of a circulating form of vitamin D –known as 25-hydroxyvitamin D – in their blood of about 80 to 120 nanomoles/litre. But the average was far lower, at only 58 nmol/L.
Cancer spread – also known as metastases – was also associated with vitamin D status. The researchers found women with insufficient levels were 94 per cent more likely to have the disease spread by 10 years after diagnosis than those with sufficient levels.
Dr. Goodwin also cautioned that while the research has found an association between vitamin D and cancer progression and death, proving conclusively that low levels were the cause would require a drug-style trial.
Nonetheless, 10 years after their diagnoses, 85 per cent of the women with sufficient levels of vitamin D were still alive, but only 74 per cent of those with deficiencies.
Dr. Goodwin said that women don’t have to be part of a research program to have their vitamin D levels checked because provincial health plans will pay for the test, if ordered by a doctor, and she said it is a good idea for women worried about the nutrient to have such an analysis done.
Women can raise their blood levels of vitamin D through increased spring and summer sun exposure – with experts typically recommending short periods to minimize skin cancer risk – and through supplements.
Breast cancer is expected to strike about 22,400 Canadian women this year, making it the leading cause of cancer among women. An estimated 5,300 will die from it.
source: The Globe and Mail