Four Cups a Day: What the Studies Say About Coffee and Health

Two cups, the headline says, aren't enough. The claim comes from an Inverse piece published in June 2018, and it rests on a new study in PLOS Biology and a run of earlier research, all pointing toward roughly four cups of coffee a day as a level that may do the body some good.

Start with the heart, where coffee's reputation has been worst. Critics have long held that it harms the heart, and since too many cups make people jittery, that view has gone largely unchallenged. The PLOS Biology study argues otherwise. Its co-authors, Joachim Altschmied and Judith Haendeler, both biologists at the University of Dusseldorf, told Inverse: "We've disproved what doctors have told your grandma: Don't drink coffee if you have a heart problem."

Their finding is about mechanism. They say four cups a day delivers enough caffeine to push a protein called p27 into the mitochondria of heart cells, which helps those cells work more efficiently. Altschmied adds that it is already known that four or more cups lower the risk of heart attack, stroke, and diabetes.

The article then lists four benefits drawn from other work. The first is again the heart. Researchers at Sungkyunkwan University in South Korea, led by Dr. Yuni Choi, screened more than 25,000 men and women. Those who drank three to five cups a day were less likely to show coronary artery calcium, an early sign of heart disease.

The second is colorectal cancer. A University of Southern California study found coffee drinking was tied to a 26 percent lower chance of developing the disease. For people drinking more than 2.5 servings a day, the reduction reached as much as 50 percent. The pattern held even for decaf drinkers. Lead author Stephen Gruber said the team was somewhat surprised that caffeine did not seem to matter, which indicates caffeine alone is not responsible for coffee's protective properties.

Third is Alzheimer's disease. Several studies suggest caffeine may protect against dementia, and researchers are beginning to look at long-term effects on cognition beyond the short-term stimulation of the central nervous system. One Portuguese study found coffee drinkers had up to a 65 percent lower risk of Alzheimer's, which the article says could open possibilities for preventing or delaying its onset.

Fourth is the liver. Hepatitis, fatty liver disease, and chronic alcoholism can all lead to cirrhosis, the scarring of the liver. Separate studies in the United States and Italy found that people drinking four or more cups a day had up to an 80 percent lower risk of cirrhosis, especially the alcohol-related kind.

The piece closes on the idea that coffee, unlike other caffeinated drinks, is giving scientists distinctive clues about disease prevention, which suggests it is more than a stimulant. Worth keeping in mind: the article relays these studies secondhand, and much of the evidence is observational, showing association rather than proof of cause. Anyone thinking of changing their habits would do well to read the original studies first.