Stuart MacGregor, an associate professor of statistical genetics, embarked on the study to find the answer to this controversial conundrum. His team at QIMR Berghofer in Queensland found that daily coffee consumption is neither harmful nor protective after analysing data from more than 300,000 people.
“It’s quite a controversial area,” he said from Brisbane. “There has been quite a lot of work done on this already, and a few of the recent studies have been suggesting there could actually be a protective effect from increasing consumption on cancer risk.”
But there are flaws in many of those these papers, including publication bias. Whenever it is suggested that changing a modifiable risk factor will alter someone’s disease risk, the idea immediately becomes more newsworthy, prompting academics to go ahead with publishing their findings.
Another problem was the confounding issue of coffee drinking and lifestyle activities that often go with it, such as smoking, diet and exercise levels. It isn’t necessarily the coffee that causes or prevents the cancer, but the associated activities.
“What we did was take do a big study that was bigger than most of the previous studies, and we took a slightly different angle: we took a genetic predisposition for how much coffee the subjects had, and we used that to try to look for a link between coffee consumption and cancer risk,” explained MacGregor.
“By doing things in that way you can make a stronger statement, in this case disproving studies showing a link between coffee and cancer.”
The two-pronged study looked at whether cancer rates differed among people with different levels of self-reported coffee consumption, and whether the same trend was seen when his team replaced this consumption with genetic predisposition towards coffee consumption.
They found there was no real relationship between how many cups of coffee a person had a day and if they developed any particular cancers. The study also ruled out a link between coffee intake and dying from the disease.
Coffee contains a complex mixture of bioactive ingredients, including substances such as caffeine and kahweol, which have been shown to display anti-tumour effects in animal studies.
Its potential anti-cancer effect on humans has not been established however, with studies to date producing conflicting findings for overall cancer risk and for individual cancers such as breast and prostate cancers.
MacGregor said the study had implications for public health messaging around the world.
“The health benefits of coffee have been argued for a long time, but this research shows simply changing your coffee consumption isn’t an effective way of protecting yourself from cancer,” he said.