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The science in favor of coffee: Six key studies

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In helping to draft the next set of Dietary Guidelines for Americans, an expert federal panel offered this good news about coffee.

“Moderate coffee consumption can be incorporated into a healthy lifestyle,” the group wrote. By moderate, the group meant three to five cups per day, or about 400 milligrams of caffeine.

Their conclusions were based on a review of dozens of studies conducted over the years. When all of the results of those studies are totted up in research efforts known as meta-analyses, the data indicated either that coffee seemed to bear no relation to heart disease and mortality, or indicated that moderate coffee intake was associated with health benefits, not harm.

In their summary of the evidence, the group said the evidence was “strong and consistent” that moderate coffee consumption has nothing to do with chronic diseases such as heart disease and cancer. Indeed, coffee seemed to be associated with better health.

“Consistent observational evidence indicates that moderate coffee consumption is associated with reduced risk of type 2 diabetes and cardiovascular disease in healthy adults,” the group said, though it warned against taking up coffee for health advantages.

The observational evidence is not perfectly consistent, however. For example, a study involving more than 43,000 people published in 2013, showed that coffee drinkers less than 55 years old had a significantly higher mortality rate.

Listed below are some of the key studies cited by the expert panel as support for their opinion. While the group reviewed the evidence on the connection between coffee and other diseases, a focus of the research involves possible links between coffee and heart disease/ mortality, which are the subjects of these studies.

For the other side of the argument, read the key studies that link coffee to heart attacks and hypertension, which is linked here.

“Long-Term Coffee Consumption and Risk of Cardiovascular Disease: A Systematic Review and a Dose-Response Meta-Analysis of Prospective Cohort Studies”
Circulation, November 2013

Finding: This study, which with 1.2 million subjects was one of the largest, suggested that drinking three cups a day might be good for you. It indicated that drinking about 3.5 cups per day was associated with a 15 percent reduction in heart disease. Drinking about five cups a day, meanwhile, did not raise heart disease risks compared to people who drank very little coffee or none at all.

Coffee consumption and risk of coronary heart disease: a meta-analysis.
Nutrition, Metabolism & Cardiovascular Diseases, December 2006
Finding: While this paper is cited as evidence by the panel for its coffee finding, it seems fairest to see this as a split decision. The researchers looked at two types of research - cohort studies, which look at large groups over time, and case-control studies, which compare people who have a disease, the “cases”, with people who don’t, the “controls.” The two methods of research turned up different results. When researchers totted up the results from ten cohort studies, they found no association between coffee drinking and heart disease. When they totted up the results from the case-control studies, though, they found that people who drink more than three cups per day seemed to be at higher risk of heart disease.

Coffee consumption and risk of coronary heart diseases: A meta-analysis of 21 prospective cohort studies
International of Cardiology, November 2009
Finding: There was no overall association between coffee consumption and heart disease, although it appeared that in women moderate coffee drinking was associated with a lower risk of heart disease.

A meta-analysis of prospective studies of coffee consumption and mortality for all causes, cancers and cardiovascular diseases
European Journal of Epidemiology, July 2013
Finding: Drinking more coffee was associated with a lower rate of death.

Coffee consumption and mortality from all causes, cardiovascular disease, and cancer: a dose-response meta-analysis.
American Journal of Epidemiology, October 2014
Finding: People who drank three or four cups of coffee a day had the lowest risks of death by any cause, or death by heart disease.

Coffee consumption  and total mortality: a meta-analysis of twenty prospective cohort studies
British Journal of Nutrition, April 2014
Finding: This meta-analysis of twenty studies indicated that mortality rates were lower for people drinking more coffee than for those drinking less. The apparent benefits seemed stronger in Europe and Japan than in the United States.