Researchers have been investigating the links between coffee and cancer for decades. But there is still a lot they don’t know. In 2016, an expert panel convened by the International Agency for Research on Cancer (IARC) – the arm of the World Health Organization that is responsible for assessing whether certain substances cause cancer – could not conclude that drinking coffee is carcinogenic based on the current evidence available.
And now the coffee-cancer connection is in the news again. A California court ruling last week about a coffee warning related to a chemical formed during the roasting process (called acrylamide) has raised questions among consumers.
So, what do coffee drinkers need to know? In this interview, American Cancer Society researchers, Susan Gapstur, PhD, and Marjorie McCullough, ScD, provide insights into what studies to date really show when it comes to coffee and cancer, and discuss what other research is still needed.
Q. What does the research show about the link between coffee and cancer?
A. Numerous studies have shown that coffee drinking is associated with a lower risk of dying from all causes of death. However, associations with cancer overall or with specific types of cancer are unclear. In 2016, an expert working group convened for the International Agency for Research on Cancer Monographs Programme reviewed the world’s body of human and laboratory research on coffee drinking and cancer risk, and they found the evidence of carcinogenicity of coffee drinking to be “unclassifiable”.
They also found that coffee drinking is not a cause of female breast, pancreas, and prostate cancers, but may reduce the risk of uterine endometrium and liver cancers. The evidence was judged to be inadequate for other cancer types. Reasons for the lack of convincing evidence included inconsistent results across studies and issues with data quality.
Additionally, because smokers also tend to be coffee drinkers, it is difficult to completely account for tobacco use in studies of coffee and strongly tobacco-related cancers. These issues can be addressed by examining risk in non-smokers, or with detailed statistical adjustment for smoking. For example, early research suggested that coffee increased the risk of bladder cancer, but the true causal factor was later found to be smoking.