A 1994 survey by the Academy of Emergency Medicine of the most widely read medical research journals found that 80 percent of published research consists of positive studies. Scientific knowledge develops incrementally over time and isn't a one-study endeavor. Be wary of any one study. It's likely to mean less than it claims. Another problem with these ominous studies is that their relevance to the individual is often oversold.
Much research relies on epidemiology, the study of disease in actual human populations.
But epidemiology's strengths are also its Achilles' heel. Epidemiology is about observed rates of disease in particular small populations, not future risks to all beings. Many individuals will be at greater risk of cancer and many will be at lower risk. And most of the time it's impossible to identify with any accuracy who's at greater risk. But claims of causation are rarely true.