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Wednesday November 5, 2008 (foodconsumer.org) -- Taking vitamin B supplements like folic acid, vitamin B 6 and vitamin B 12 regularly may not help prevent cancer, according to a new study led by Dr. Shumin Zhang and colleagues at Brigham and Women's Hospital and Harvard Medical School.
The study published in the Journal of the American Medical Association followed 5,442 female health professionals at the average age of 63 in the United States for 7.5 years and found taking B vitamins pills did not reduce risk of cancer or risk of dying from cancer. The women had cardiovascular disease or risk factors like high blood pressure or high cholesterol levels.
The researchers found, however, among women aged 65 and older, those getting the daily B vitamins had a 25 percent reduced risk of developing any type of cancer and a 38 percent reduced risk of developing breast cancer.
A health observer cautioned that regardless of the findings, the study was not a trial and the results of it did not mean to say that taking vitamin B supplements are useless or definitely prevent cancer. Trials are needed to confirm any findings.
The study is not the first looking at the link between vitamin B supplements and risk of cancer. And some have found some positive associations.
One study published in the June 1 2007 issue of Cancer Research found that high dietary intake of b vitamins like folate, vitamin B6 and vitamin B12 reduced risk of pancreatic cancer by 81 percent, 73 percent and 59 percent respectively compared to low intake of these vitamins.
The study led by Eva Schernhammer, M.D., Dr.P.H. of medicine at Harvard Medical School and colleagues also found that supplementation of these B vitamins were linked with increased risk of this rare yet lethal malignancy.
According to the researchers, study participants who reported they used multivitamins and whose blood carried only traces of these B vitamins had a 139 percent increased risk of developing pancreatic cancer.
"All we can say is that a person who has reason to be concerned about their risk of developing this cancer, which is relatively rare but quite deadly, should maintain a normal weight and eat their fruit and vegetables," said Schernhammer.
They compared food intake and vitamin use in 208 pancreatic cancer and 623 cancer free controls and found these associations.
The study was not meant to provide any explanation as to how B vitamins reduce or increase risk of the cancer. But Dr. Schernhammer speculated that B vitamins may fuel growth of existing pancreatic cancer.
Some animal studies suggest that "if there is a dormant tumor, folate and other similar vitamins may stimulate growth."
Dr. Schernhammer said this may be the same case if a person does not take enough of these vitamins consistently through diet, and then suddenly take vitamins supplements.
But the question is why the dietary B vitamins did not increase the cancer risk? No one knows anything for sure. But the dose may make the difference.
One study in the journal Gut found people with either high or low levels of folate in the blood had lower risk of colorectal cancer, but those with moderate levels were twice as likely to develop the disease.
The study led by researchers from Umea University, Sweden involved 226 people with colon cancer and 437 controls from the Northern Sweden Health and Disease Cohort. Participants were surveyed for their lifestyle including diet and blood samples were analyzed for circulating serum levels of folate.
While epidemiological studies yielded inconstant conclusions, some laboratory studies support the notion that vitamins prevent cancer.
One animal study published in the December 2007 issue of the Journal of Nutrition showed that mild deficiency of dietary folate and other B vitamins alters multiple components of the Wnt pathway, raising risk of colorectal cancer.
Early preclinical and clinical studies suggest that depletion of folate increases the risk of colorectal carcinogenesis.
Biochemical functions of folate depend on the adequate availability of other 1-carbon nutrients such as riboflavin, vitamin B-6 and vitamin B-12, prompting researchers to believe that deficiency of other B vitamins may also play a role in the increased risk of colorectal cancer.
In the study, Z Liu from Tufts University and colleagues from University of Southern California and Harvard Medical School fed 96 mice diets with different combinations of B vitamin depletion for 10 weeks.
They found DNA strand breaks within the Apc mutation cluster region were induced by folate depletion and inadequate availability of riboflavin, vitamin B-6 and vitamin B-12. But this effect was not seen when folate alone was deficient.
Apoptosis, programmed cell deaths that are missing in cancer cells, was attenuated by the combined deficiency of B vitamins, but not by deficiency of one or two single nutrients, Liu and team found.
All the evidence suggests that B vitamins together are important in fighting cancer.
Folate is found in many foods including bananas, oranges, leafy green vegetables, asparagus, broccoli, and many sorts of beans and peas, and fortified cereals. Vitamin B6 is found in fortified cereal, bananas, salmon, turkey, chicken, potato, spinach and vitamin b 12 is found in clams, mussels, crab, salmon, and beef, to name a few. |
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