Soft Drinks and Pancreatic Cancer: A Plausible Link?
Late last night the press began reporting on a press release from the authors of "Soft Drink and Juice Consumption and Risk of Pancreatic Cancer: The Singapore Chinese Health Study". By this afternoon the claim that drinking as few as two soft drinks a week may nearly double the risk of getting one of those "go get your affairs in order" cancers had appeared on nearly every major news site. So what to make of it?
First it's probably wise to read up on the Singapore Chinese Health Study. How was dose (number of soft drinks per week) determined? It looks as though it was done via questionnaire rather than any objective measurements. And how many cases were there? 140; which isn't many thereby pushing the reported hazard ratio of 1.87 to the "slight" end of the range of the scale used to weigh evidence when making causal inferences.
Second let's look at the other claims on which the authors rely to support their causal hypothesis: specifically, a) Increased sugar intake may stimulate tumor growth through effects of insulin; and b) Pancreatic cancer rates increased nearly twofold over the past several decades.
As we reported recently there is indeed evidence tending to show that chronic moderate to high levels of glucose in the blood are associated with an increased risk of pancreatic cancer. Sounds supportive, right? Only if drinking sweetened soda chronically elevates blood sugar levels. And here's an article that says that it doesn't - not in lean men, not in obese men and not even in type 2 diabetic men; and not even at 75 grams of sucrose per day (seven times the purported risk elevating level referenced in today's article under discussion). So maybe it's like the fat follies of the past few decades; eating fat makes you fat, right? Wrong. Similarly, maybe the association between consuming sugar and hyperglycemia isn't so simple. And isn't that doubt furthered by the finding that sugary fruit drinks were NOT associated with pancreatic cancer?
Finally, here's the SEER Stat Fact Sheet for cancer of the pancreas. As noted there are lots of ways to look at trends but from the SEER perspective the upward trend in pancreatic cancer incidence and mortality is quite recent and looks to be driven by an increase among women. Doesn't that suggest smoking? It is after all the most consistently identified causative factor in cancer of the pancreas.
