Can selenium prevent cancer? Is there really a Santa Claus?
Yes, Virginia, selenium CAN prevent cancer. Unfortunately, you would need to take a lethal dose of selenium. You might not see another Christmas, but at least you can say you prevented cancer!
On Christmas Eve, just as Santa began to make his annual rounds, network TV news reported that the element selenium (faithful readers of the periodic table of elements know it as "Se") may prevent cancer if ingested in sufficient, but non-toxic, amounts.
Not only was selenium the lead story on ABC World News, but ABC was so impressed that it did a selenium reprise at the end of its half-hour news program.
Naturally, I was intrigued. So I broke out my copy of the Journal of the American Medical Association. I quickly became un-intrigued.
First, the study was not designed to test whether selenium could prevent any and all cancers. The study was designed only to test whether selenium prevented skin cancer. Because it was not designed to consider the many potential (if not likely) biases and confounding risk factors relevant to overall cancer prevention, the study likely was likely inadequate to pass judgment on the overall cancer prevention issue.
Ironically, Clark et al. could not even associate selenium with a reduction in skin cancer incidence!
But faced with the likelihood of having a non-publishable study (typically, scientific journals are about as interested in negative studies as tabloid newspapers are in inspirational Christmas stories), the ever-resourceful Clark et al. reached for the stars.
Citing studies that report selenium to have an anti-tumorogenic effect in animals, Clark et al. married this THEORY to the observed reduction in overall cancer incidence among their study population (i.e., 37 percent less cancer in the group who took selenium).
Nice try. But no cigar! At least not yet.
Selenium was associated with a slight decrease in all cancers taken together, particularly lung, prostate and colorectal cancer. But, selenium was NOT associated with decreases in leukemia or breast, esophogeal, skin, bladder and other cancers.
Given that Clark et al. have postulated that selenium acts through some GENERAL cancer prevention mechanism, they have a lot of explaining to do about why selenium only had an effect on SOME types of cancer.
Also, selenium was only WEAKLY associated with decreased cancer incidence. It is elementary epidemiology that weak associations are not reliable. Clark et al.'s conclusion is doubly suspect given that the study was not designed to examine overall cancer prevention.
Nevertheless, Ebeneezer, this study has a potentially bright side.
Over the last 30 years, public health researchers and environmentalists have been at war with the periodic table of elements. Lead, arsenic, mercury, chlorine, radon, radium, sodium, plutonium, cadmium, etc. You name the element, they say it's bad for us. Maybe this study will signal a comeback for the period table and its elements.
Finally, even if selenium doesn't prevent cancer, it still has uses. For example, selenium is the active ingredient in dandruff shampoo. That's appropriate, considering these very flaky yuletide conclusions.