Coffee Doesn't Cause Cancer After All, Says World Health Organization

There's no reason to think coffee will give you cancer unless you drink it while it is scalding hot, according to a new report by the World Health Organization.

Drinkers of the delightful black liquid are able to breathe a sigh of relief after the announcement from WHO's International Agency for Research on Cancer, which had previously classified coffee as "possibly carcinogenic."

However, the details might be a little more unsettling: Instead of calling coffee "possibly carcinogenic" in the new review published in the Lancet the agency now says it is "unclassifiable."

What does that mean? Well, it means that the evidence on the cancer-causing effects of coffee are far too muddled and contradictory to make a definitive judgment.

This is something of a surprising result, since the the WHO reviewed more than 1,000 studies. For a few cancers, including pancreas, female breast and prostate cancer, there was no evidence of coffee as a contributing factor. In the case of liver and uterine endometrium cancers, coffee actually appears to be somewhat preventative. 

But for 20 other forms of cancer reviewed, the evidence was not clear either way. Coffee might lead to cancer, or it might not, and there's no particular reason for us to lean one way or the other.

That is, unless it is piping hot. 

At temperatures of more than 158 degrees, any beverage — not just coffee — can increase the likelihood of developing esophageal cancer. Liquids at these temperatures are now considered "probably carcinogenic to humans."

The researchers reached this conclusion after reviewing epidemiological studies in Iran, China, Turkey and South America, where drinks like tea and mate are commonly consumed at very high temperatures. People who drink these beverages cold do not see an increase in rates of esophageal cancer, indicating that the high heat is the cancer-causing factor.

“Smoking and alcohol drinking are major causes of oesophageal cancer, particularly in many high-income countries,” Dr. Christopher Wild, president of the agency, said in a statement. “However, the majority of oesophageal cancers occur in parts of Asia, South America, and East Africa, where regularly drinking very hot beverages is common and where the reasons for the high incidence of this cancer are not as well understood.”

The statement also notes that esophageal cancer is responsible for 5 percent of cancer deaths, though it is unclear what portion of those could be linked to the consumption of hot beverages.

According to David Sampson from the American Cancer Society, we shouldn't be too shocked that WHO is making these kinds of changes to its classification of coffee. 

"Some may see this change as a sign that 'science can’t make up its mind,'" he wrote in a statement. "In fact, this is what makes science powerful: its willingness to seek and consider the totality of the evidence and interpret evidence that challenges what we previously believed."

Still, some might find it a bit frustrating that we have more than 1,000 studies on the relationship between coffee and cancer, and the best WHO can say is that it's unclassified.

It makes you feel like you're going to need at least a second cup.

Photo Credit: Jen via Flickr