Does hot coffee cause cancer?

*US judge ruled drink is carcinogenic, must carry warning label
*Product produces acrylamide when heated, tampers with DNA
*No evidence that humans consume enough to induce tumour

Americans will soon be taking their coffee with cream and a cancer warning, after a Californian 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 is what Medical News Today knows — and do not know — about coffee’s health effects, both good and bad.

What is 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 is 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.

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

Also, a review of available evidence on coffee drinking and the risk of all cancers and selected cancers published in European Journal of Cancer Preview 2017 September concluded that coffee consumption is not associated with overall cancer risk.

A meta-analysis reported a pooled relative risk (RR) for an increment of one cup of coffee/day of 1.00 [95% confidence interval (CI): 0.99-1.01] for all cancers. Coffee drinking is associated with a reduced risk of liver cancer. A meta-analysis of cohort studies found an RR for an increment of consumption of one cup/day of 0.85 (95% CI: 0.81-0.90) for liver cancer and a favorable effect on liver enzymes and cirrhosis. Another meta-analysis showed an inverse relation for endometrial cancer risk, with an RR of 0.92 (95% CI: 0.88-0.96) for an increment of one cup/day.

A possible decreased risk was found in some studies for oral/pharyngeal cancer and for advanced prostate cancer. Although data are mixed, overall, there seems to be some favorable effect of coffee drinking on colorectal cancer in case-control studies, in the absence of a consistent relation in cohort studies. For bladder cancer, the results are not consistent; however, any possible direct association is not dose and duration related, and might depend on a residual confounding effect of smoking.

A few studies suggest an increased risk of childhood leukemia after maternal coffee drinking during pregnancy, but data are limited and inconsistent. Although the results of studies are mixed, the overall evidence suggests no association of coffee intake with cancers of the stomach, pancreas, lung, breast, ovary, and prostate overall. Data are limited, with RR close to unity for other neoplasms, including those of the esophagus, small intestine, gallbladder and biliary tract, skin, kidney, brain, thyroid, as well as for soft tissue sarcoma and lymphohematopoietic cancer.