STATS ARTICLES 2010

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Can soda give you pancreatic cancer?
Rebecca Goldin, PhD, February 11, 2010
Pancreatic cancer is one of the deadliest forms of cancer, with five-year survival rates under five percent. And it could be caused by something you drink every day: soda. Then again, maybe not.

The causes behind pancreatic cancer are still not well understood, though many have hypothesized based on correlates. It is known that smoking increases the risk of pancreatic cancer (and this association is, at this point, assumed to be causal). But when it comes to other risk factors, such as obesity and type 2 diabetes, it may not be that obesity or diabetes is by itself a risk factor. Rather, they may reflect other, more relevant risk factors, such as abnormal glucose tolerance. The theory goes that increased sugar intake (via sugar soda) increases blood glucose levels, which may in turn create a “favorable environment” for pancreatic cancer.

A recent study to appear in the journal Cancer Epidemiology, Biomarkers & Prevention set out to ask whether (sugared) soft drink consumption increases the risk of pancreatic cancer among Chinese men and women living in Singapore. The study included about 60,000 individuals, and compared those people who were drinking at least two eight-ounce servings per week of soda -- paltry compared with the American average of about 17 similarly-sized servings per week -- with those who were drinking none per week.

The results? For people who drank at least two servings of sugar soft drinks a week, soda seemed to be a serious risk factor for pancreatic cancer, with a hazard ratio (after adjustment for potential confounders) of 1.87 and a 95 percent confidence interval of 1.09-3.21. There were many differences between those who “do” drink soft drinks and those that don’t -- soft-drink drinkers tend to be male, have more education, have been more likely to smoke, eat more red meat, consume more calories, and have a higher Body Mass Index (BMI) than those who don’t drink soda. 

By contrast, juice did not have the same correlation with pancreatic cancer in the Chinese study. Though the adjusted hazard ratio was above 1.0, the result did not reach statistical significance. According to the authors of the article, while juice contains a lot of sugar, it has a smaller effect than soft drinks on glucose and insulin levels. In addition, juice may be associated with other, healthier life-styles that reduce the risk of pancreatic cancer and counter possible bad effects from the sugar in juice.

This study stands in agreement with some other similarly-sized studies, but it also stands in stark contrast to  very large studies examining this very relationship in the United States, where extreme soda consumption would suggest the link would be easier to see.

No association, for example, was found in a study about ten times as large conducted via a National Institutes of Health-AARP survey of almost 600,000 people. This study was published in 2008 in the American Journal of Clinical Nutrition. It might be significant that the Americans were significantly older than the Chinese. However, there was no association between sugar sodas, or even sugar in general, and pancreatic cancer. This study considered sodas, juice, sugar added to coffee or tea, sweets, diary desserts and other sugar-sweetened foods. By combing through the analysis, one can find some interesting “tidbits”, such as the fact that if one has a high level of physical activity, there seems to be an overall benefit to consuming a lot of sugar. That said, these observations are likely to be statistical anomalies, as the possible benefit is not seen when restricted to soft-drink consumption as opposed to overall sugar consumption. 

The authors of this earlier American study note that with a sample this large, to miss such an association would be unlikely if one actually exists. In other words, if pancreatic cancer were linked to sugar intake in a moderate way, it should have been observed; and yet, it wasn’t.

Possible reasons for different results in different studies

There are limits to both of these studies, notably the self-reports of food and soda consumption. In both cases, dietary changes could not be addressed. Similar problems persist with other studies, most of them small, some finding an association and some not.

Other possible explanations for the different findings in these two papers include that white people (which comprised most of the NIH-AARP data set) are less susceptible to pancreatic cancer due to sugar than people of Chinese descent. A Canadian study of just under 50,000 women found no association as well, further bolstering the possibility that different gene pools have different susceptibility. But a study involving the Nurses’ Health Study data did find an association among sedentary and overweight women, suggesting that women of European and African descent are not immune. .

It could be that the American study did not follow people long enough; they followed people on average for seven years, compared to over ten years in the Chinese study. On the other hand, it may be that younger people (in the Chinese study) are more likely to suffer the consequences of a high-soft drink diet than the older people in the American study. However, the Canadian study followed women for 16 years with no effect.

Yet another possibility is that the data are clouded by other factors. It may be that the Chinese study shows an effect precisely because the contrast between soda and the rest of their diet is so strong. On the other hand, it could well be that the Chinese study did not note other “Western” behavior that encourages the onset of pancreatic cancer that may have been correlated with soda drinking. The overall rate of pancreatic cancer for the Chinese population in Singapore is slightly more than 1/2 the rate of the same cancer in the United States -- a phenomenon that could also be related to the efficacy of tracking the cancer.

What’s the overall conclusion? The chips (and soda) aren’t in. The reasons for cutting back on sugared soda drinks may be plentiful enough without worry about pancreatic cancer (consumption of sugared soft drinks is correlated with obesity and type 2 diabetes) but in terms of pancreatic cancer, the evidence against soft drinks is not conclusive. And given that the risk of pancreatic cancer is so low, at about one in nine thousand per year in the United States, the new research does not justify panicking over how much soda you downed watching the superbowl.

 

How not to report a study

So how should a study screaming "Cancer Cola" be covered? Certainly, not as "Cancer Cola," which is how CBS News decided to report the study:

"Mothers have warned for decades that drinking too much soda might cause cavities, but those sugar-laden beverages may expose people to a much greater risk - cancer.

A recently released study from the University of Minnesota finds that people who drink as few as two soft drinks a week face almost double the risk of pancreatic cancer, one of the deadliest forms of the disease, according to a report by CBS station WCCO-TV.

"Their risk of getting pancreatic cancer over the time period of the study was almost two times higher than their counterparts who were consuming little or no sugar-sweetened beverages in the study," said Dr. Mark Pereira."

CBS added zero context to the numbers, either in terms of the key data in the study showing that the number of pancreatic cancers was extremely low to begin with - or in terms of previous large studies that found no such link. And the result is that any reasonable person scanning the article would find it hard not to conclude that drinking more than two sodas a week had worse odds than playing Russian Roulette. 

Trevor Butterworth

 


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