For years, coffee was regarded as an unhealthy indulgence and even a possible carcinogen, but research shows coffee is not a carcinogen and suggests that the beverage is associated with better health outcomes when consumed in moderation, Dawn MacKeen reports for the New York Times.

Cheat sheets: Evidence-based medicine 101

Coffee was thought of as a carcinogen

Part of coffee's bad rap stemmed from the belief that it was a carcinogen. When a coffee bean is roasted, it produces the chemical acrylamide, which according to the American Cancer Society (ACS), has been shown to increase the risk of cancer in mice and rats when it is placed in the animals' drinking water at doses "1,000 to 10,000 times higher than the levels people might be exposed to in foods." The belief even prompted a lawsuit in 2010 to push California's coffee industry to eliminate acrylamide from the roasting process and include a warning label on the beverages.

However, public health experts have cautioned against extrapolating results from animal trials to humans, and recent research has even suggested that coffee might actually reduce the risk of developing several cancers. As a result, the World Health Organization in 2016 removed coffee from a list of "possible carcinogens," stating there is "no conclusive evidence for a carcinogenic effect of drinking coffee."

How coffee shook the bad rap

Around the same time that WHO removed coffee from the "possible carcinogens" list, the drink's image got a big boost from U.S. dietary guidelines, MacKeen reports. In 2015, HHS issued dietary guidelines that, for the first time, recommended moderate coffee drinking as part of a healthy diet.

Previous research on coffee hadn't controlled for lifestyle factors, like whether heavy coffee drinkers were also smokers, MacKeen reports. Once it did, it showed that coffee was actually good for you.

According to Erikka Loftfield, a research fellow at the National Cancer Institute, "The evidence is pretty consistent that coffee is associated with a lower risk of mortality."

One 2017 review in the BMJ found that, the majority of the time, coffee was associated with a health benefit, not a harm. For that review, researchers looked at over 200 other study reviews and found that moderate coffee consumption was associated with lower rates of cardiovascular disease and premature death from all causes.

That said, Jonathan Fallowfield, a professor at the University of Edinburgh and co-author of the BMJ study, cautioned that much of the research on coffee's health benefits has been observational and therefore correlational rather than causal. "We don't know for sure if coffee is the cause of the health benefits," he said. "These findings could be due to other factors or behaviors present in coffee drinkers."

Remember moderation

And while recent research points to associations between coffee consumption and health, scientists say it's important to remember to consume caffeine in moderation, not excess.

There isn't much research on how having more than 400 milligrams of caffeine a day will affect a person's health, according to HHS' dietary guidelines, but it's possible higher doses of caffeine might cause caffeine intoxication, which leads to shakiness, nervousness, and irregular heartbeat.

Limiting caffeine consumption is particularly important for certain populations, MacKeen reports. For instance, some health care providers recommend expecting mothers cap caffeine consumption at 200 milligrams a day or less because caffeine can travel through the placenta to the fetus. That said, according to the American College of Obstetricians and Gynecologists, research has yet to determine how much caffeine is safe to consume during pregnancy.

Another group that should be careful when drinking coffee are people who metabolize caffeine slowly, MacKeen reports. According to Giuseppe Grosso, an assistant professor in human nutrition at University of Catania in Italy, some people have a genetic variant that slows the metabolism for caffeine, leading them to drink several cups of coffee but only experience the caffeine intake of having consumed one cup.

But for the average person, doctors say drinking coffee in moderation shouldn't cause any concern, MacKeen reports. Sophie Balzora, a gastroenterologist and clinical associate professor of medicine at NYU School of Medicine, said, "Robbing people of their coffee seems cruel" (MacKeen, New York Times, 2/13).