The epidemiologists at the National Cancer Institute who conducted the study, which appeared in last week’s New England Journal of Medicine, were cautious in interpreting the results. People in the study who drank coffee – 90 percent of the overall group – were more likely to smoke. That more than wiped out any gains from coffee drinking.
But even that group showed benefits from having a morning cup of java or five. “There was a similar effect among former smokers and a weaker effect – not statistically significant – in current smokers,” said Neal Freedman, an investigator in the division of cancer epidemiology and genetics at NCI.
There are more than a thousand chemicals in coffee, so it is impossible to pinpoint or even guess what might be responsible for the positive benefits associated with heavy coffee drinking. The make-up of the brew is also affected by how it is made and the type of beans, where they come from and how they are roasted, none of which was measured in the survey.
Previous association studies have shown coffee drinkers are less likely to develop Alzheimer’s or Parkinson’s disease, suffer gallstones or develop heart disease. A few studies have shown reduced incidence of various forms of cancer, but most have come up empty on that front. The largest – the Nurses Health Study that followed over 100,000 nurses recruited in 1989 – showed a 17 percent reduction in risk of early mortality, similar to the current study which covered both men and women.
This latest study followed more than 402,260 older adults – members of AARP between the ages of 50 and 71 – between 1995 and 2008. Observational studies (as opposed to controlled clinical trials) cannot make definitive claims about cause and effect since they only show an association between a behavior and a result.
The researchers only surveyed the coffee drinking habits of the participants when they first enrolled in the study. Yet Freedman is fairly confident about the results. “People may have changed the amount of coffee they drink, but coffee drinkers tend to drink the same amount of coffee over their lives,” he said.