Junkfood Science: Vitamins and prostate cancer

May 16, 2007

Vitamins and prostate cancer

Millions of men came home from work to be greeted by news that the vitamins they’ve been taking, believing to be good for them, could increase their risks for prostate cancer.

For years, we’ve heard that preventing cancer means a healthy diet with lots of fruits and vegetables, and rich in vitamins, anti-oxidants and all that jazz. But a new study reported that men most conscientiously following a healthy lifestyle had higher risks of advanced and fatal prostate cancers. According to Reuters:

Too Many Vitamins Could Raise Prostate Cancer Risk

Men who pop too many vitamins in the hope of improving their health may in fact be raising their risk of the deadliest forms of prostate cancer, especially men with a family history of the disease, researchers said.... The researchers followed 295,344 men over five years to see if there was a link between multivitamin use and prostate cancer.

“We didn't see any relationship with overall prostate cancer," said Dr. Michael Leitzmann, a National Cancer Institute investigator who worked on the study.... In men who took too many multivitamins, the risk of aggressive cancer increased by one third, and the risk of fatal prostate cancer doubled compared to those who took no multivitamins...

The study, led by Karla A. Lawson, Ph.D., at the National Cancer Institute in Bethesda, MD, looked through the NIH-AARP Diet and Health Study database for over 295,000 men who had returned questionnaires that had been mailed to 3.5 million AARP members in 1995-6. The men had answered food-frequency questions, as well as questions on their vitamin usage, family history, demographics and lifestyles. The researchers searched through cancer registries to identify prostate cancers that had been diagnosed five years later. The AARP database was used to look for associations with the men’s diet and vitamin usage. They found no association at all between vitamin usage and total or localized prostate cancers. There was also no association between advanced cancers and vitamins taken up to seven days a week. But one or more extra vitamin a week jumped their risks for advanced cancers by 32% and fatal cancers by 98%.

As we know, these types of data dredges looking for risk factors — associations — that are meant to alarm us, needn’t. The relative risk numbers the researchers found, while they may sound impressive, were also way under what would be considered tenable for these types of studies. This study, in essence, was a nonfinding.

The most valuable message we can take away from epidemiological studies of nonfindings like this one, is what not to concern ourselves about. In this case, vitamins don’t have special abilities to prevent or protect men from prostate cancers. And in fact, the researchers couldn’t find that any single vitamin or supplement made any difference in risks. So much for the magic of vitamin pills.

Other nonfindings in this study refuted other beliefs in the special cancer-fighting powers of certain “healthy” foods and lifestyles. The men taking the most vitamins and minerals (and with the highest risks for advanced and fatal prostate cancers) were those with the “healthiest” lifestyles. They had the lowest consumptions of red meat and the highest of fish and tomatoes, and they had the highest levels of physical activity. There were also fewer smokers among them, compared to the men at the lowest risks. The men with the highest risks for advanced and fatal prostate cancers were also slimmer, with lower body mass indexes than the men at the lowest risk! I wonder why they didn't headline with one of these correlations?

The news quoted one of the NCI investigators saying they didn’t know which particular vitamin was driving cancer but that their findings were “a red flag.”

We know, though, not to let epidemiological studies and their correlations get our goat. Correlations are not causation. Instead of magical beliefs that cancer is something under our control and the punishment for “bad” diets and behaviors, there were more likely explanations suggested in this study’s findings.

Cases of identified prostate cancer were associated with higher family histories for prostate cancer and among men more likely to seek PSA exams and cancer screenings. So, elderly men with family histories for cancers may have been more likely to have screenings and their cancers identified. Such a simple explanation makes more sense than that an extra vitamin pill causes cancer, doesn’t it?

PS. Want another reminder that data dredge epidemiological studies can, and do, pull out all sorts of irrelevant correlations that can even contradict each other depending on what the researchers set out to find? Another study from this very same AARP data base reported in January that “obesity” doubled men’s risks for advanced and fatal prostate cancers. The opposite this study found! The more likely explanation above applies to that study, too. :)

The next study that comes along will no doubt try to scare us with some new risk to our health. When it hits the news, we’ll just laugh and change the television channel, right guys?

Bookmark and Share