Daily consumption of less than half a cup of sugary beverages—even fruit juice—may be a risk factor for several kinds of cancer, according to a sizeable new study published this week in the British Medical Journal.

In an observational study involving over 100,000 initially healthy French adults, the majority of them women, the researchers found that an increase of 100 milliliters (about 3½ ounces, or less than a third of a 12-ounce soda) in sugary-drink intake was statistically correlated with a 22% greater chance of developing breast cancer and an 18% greater chance of developing overall cancer. The correlation was not apparent for prostate and colorectal cancers, however.

Although some earlier, smaller studies had suggested such a link, the evidence hadn’t been strong. While an observational study cannot determine causality, the researchers note that there are several reasons to believe that a high-sugar diet could increase cancer risk—for example, the fact that a high-sugar diet can contribute to obesity, itself a risk factor for cancer. But they believe that other biological mechanisms may also be at play.

“Being overweight and weight gain might not be the only drivers of the association between sugary drinks and the risk of cancer,” they wrote. “More specifically, it has been suggested that sugary drinks might promote gains in visceral adiposity [body fat concentrated around the torso] independently of body weight.”

Another pathway could be the impact of high-sugar beverages on blood sugar levels, they noted. Sugary beverages contribute to a high glycemic load, a measure of how high and how quickly one’s diet raises blood sugar, which “is associated with hyperinsulinemia [elevated insulin levels] and type 2 diabetes, both potentially involved in breast carcinogenesis,” they wrote.  

Regardless of the possible mechanisms, the main takeaway from these findings is that “reducing the amount of sugar in our diet is extremely important,” said Amelia Lake, PhD, a professor of public health nutrition at Teesside University in Middlebrough, England, who was not involved in the study, in an interview with The Guardian.

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