Aug 13, 2010 - 11:57 pm
Study shows links between survival and the vitamin as part of a balanced diet
The findings, reported in the American Journal of Clinical Nutrition, do not prove that vitamin B6 improves prostate cancer survival. But they do point to an association between survival and amounts of the vitamin that are readily attainable through a balanced diet.
Researchers found that among 525 Swedish men with prostate cancer, the one-quarter with the highest B6 intakes were 29 percent less likely than those with the lowest intakes to die of the disease during the study period.
Men in the former group averaged 2.2 to 2.9 milligrams of vitamin B6 per day, while those in the latter group got 1.3 to 1.9 milligrams daily. The recommended vitamin B6 intake for men age 50 and younger is 1.3 mg per day, while older men are encouraged to get 1.7 mg.
The protective effect of B6 appeared confined to men whose tumors had not yet spread beyond the prostate at the time of diagnosis.
When the researchers considered only these men, they found that those who got the most B6 had only 5 percent of the risk of dying as their counterparts with the lowest intakes of the vitamin.
The results offer "exciting preliminary support" for dietary factors in long-term prostate cancer survival, according to lead researcher Dr. Julie L. Kasperzyk, a post-doctoral fellow at the Harvard School of Public Health in Boston.
However, she told Reuters Health, the findings "will need to be confirmed or refuted in additional, larger studies before recommendations can be made to the general public or to prostate cancer patients."
Cancer arises from the uncontrolled growth of genetically abnormal cells -- which, in theory, means that the B vitamins could affect the development or spread of certain cancers.
For their study, Kasperzyk and her colleagues looked at the intakes of vitamins B6, B12, folate, riboflavin and methionine among 525 prostate cancer patients who were followed for up to 20 years. Few men took dietary supplements, Kasperzyk said, so the study focused on consumption from food.
Overall, 42 percent of the men died of prostate cancer during the study period. The odds were lower, however, among those with the highest vitamin B6 intakes -- although there was no evidence of protection among men diagnosed with advanced cancer.
None of the other nutrients was linked to prostate cancer survival.
Kasperzyk said that vitamin B6 has a number of functions in the body that are not shared by the other nutrients her team studied.
"What is most relevant to prostate cancer," she explained, "is the potential link between vitamin B6 and reduced responsiveness of the prostate to testosterone."
It's well known that testosterone helps fuel prostate tumors' growth and spread, and lab research suggests that B6 can dampen that response, Kasperzyk noted.
"We did not directly measure this relationship in our study," she added, "but it provides a plausible explanation."