Vitamins Reduce Cancer Risk--Relatively Speaking

A new study shows that women who take multivitamins and folic acid during pregnancy reduce the chance that their baby will develop some childhood cancers by almost 50%. Your first question on reading this should be "50% of what?"

In other words, you want to know what the absolute risk of developing pediatric cancer is. Then you can figure out whether a 50% reduction (the so-called relative risk) is a lot or a little.

Fortunately, the overall risk of childhood cancer--such as leukemia or neuroblastoma--is very low. Joseph Hall of the Toronto Star, for example, characterizes the absolute risk of neuroblastoma this way: "the disease affects about one in every 6,500 children under five years in North America."

Do the math and you realize that he's talking about a 0.015% chance of developing neuroblastoma. A 50% reduction in relative risk means that the real-world chance of developing a neuroblastoma has dropped from 0.015% to less than 0.008%.

Such a slight decrease is not a bad thing--especially when you consider how easy it is to take vitamin supplements during pregnancy and how devastating neuroblastoma can be. But most health stories in the popular media focus on relative risk and ignore absolute risk, giving you an incomplete picture.