The science behind cancer warnings on coffee is murky at best

Californians will soon be taking their coffee with cream and a cancer warning, after a court ruled that the state’s retailers must label coffee as containing a carcinogen. The decision followed an eight-year legal battle, which boiled down to a question that has plagued coffee drinkers and scientists alike: Is drinking coffee healthy, or not?

The judge’s ruling, issued Wednesday, says that Starbucks and other coffee sellers failed to show that the health benefits of the brew, which include lowering heart disease, outweigh its cancer risk. But do the new warnings mean you should put your mug down? Here’s what we know — and don’t know — about coffee’s health effects, both good and bad.

What’s in coffee that has raised cancer concerns?

When coffee beans are roasted, the compound acrylamide is produced as a by-product. “Acrylamide is ubiquitous in our food chain. It’s a product of high heat and prolonged cooking, particularly with carbohydrates,” says Len Lichtenfeld, deputy chief medical officer for the American Cancer Society in Atlanta. It’s found in fried potatoes, for example, as well as in cigarette smoke and some products such as adhesives. “It’s a chemical to which we have frequent exposure.”

Is there enough acrylamide in coffee to cause cancer in humans?

Some studies have found an increased cancer risk in mice and rats who were fed acrylamide, but those studies used doses between 1,000 and 10,000 times higher than levels that people would be exposed to in food. There have not been strong studies in humans to demonstrate the carcinogenicity of acrylamide.

While some research has linked acrylamide to kidney, endometrial and ovarian cancer, the American Cancer Society website notes that the results have been mixed and have relied on questionnaires that may not accurately reflect people’s diets.

“Most experts are going to look at the risk of acrylamide in coffee and conclude that this is not something that’s going to have a meaningful impact on human health,” Lichtenfeld says.

Is there any evidence of higher cancer rates among coffee drinkers?

A review of more than 1,000 studies found no consistent link between drinking coffee and more than 20 types of cancer, according to a working group of scientists who met in 2016 at the International Agency for Research on Cancer, a World Health Organization group. These studies examined the epidemiological evidence, meaning they looked for increased risk across populations of coffee drinkers and non-drinkers.

Are there other health problems linked to coffee?  

There’s always been a concern about the caffeine in coffee, particularly for heavy consumers.  “Caffeine can certainly have an impact on cardiac function, for example, and nervous system function,” Lichtenfeld notes.

The increasing popularity of French press coffee has also raised concern about its higher levels of cholesterol-raising diterpenes.

“But in general,” Lichtenfeld says, “it’s a beverage that, when consumed in reasonable quantities, is thought to be safe for most people.”

As for how much coffee is too much, research suggests that a few cups a day may be perfectly fine, and even better for long-term health than not drinking any coffee. One study of long-term mortality in more than 90,000 people in Japan found that three to four cups a day was optimal. Others have found no increase in mortality with up to six cups a day.

Are there health benefits of drinking coffee?

Studies have found evidence for various health benefits of drinking coffee in recent years, from helping to fend off diabetes, heart disease and stroke to protecting against depression and Alzheimer’s disease —and even, ironically, liver cancer (SN: 10/3/15, p. 16).

“My personal opinion is that I’m not telling people to give up their coffee,” Lichtenfeld says.