People with diets high in sweets and other foods that cause rapid blood-sugar spikes may have a higher risk of developing pancreatic cancer than those who eat less of those foods, a new study suggests.

In a study of nearly 1,000 Italian adults with and without pancreatic cancer, researchers found that those whose diets were high in so-called “glycemic index” showed a greater risk of the cancer than participants whose diets were relatively low-glycemic index.

Glycemic index refers to how rapidly a food causes blood sugar to rise. High-glycemic index foods, like white bread and potatoes, tend to spur a quick elevation in blood sugar, while low-glycemic index foods, such as lentils, soybeans, yogurt and many high-fiber grains, create a more gradual increase in blood sugar.

In the new study, researchers found no relationship between the total carbohydrates in participants’ diets and their risk of pancreatic cancer. And when they focused on fruit intake, higher consumption was related to a lower risk of the disease.

In contrast, there was a relationship between increased pancreatic cancer risk and higher intakes of sugar, candy, honey and jam. This suggests that sugary, processed carbohydrates - rather than carbs like fiber-rich grains, fruits and vegetables - may be particularly linked to pancreatic cancer, the researchers report in the Annals of Epidemiology.

The study follows one in February in the journal Cancer Epidemiology, Biomarkers & Prevention showing a link between sugary sodas and pancreatic cancer. Whether all of these results will hold up, however, is unclear.

Pancreatic cancer is a relatively uncommon but particularly deadly form of cancer, with only about 5 percent of patients surviving for five years. Early on, the disease causes no symptoms, or only vague problems like indigestion, so it is rarely caught before it has advanced.

Researchers, therefore, are particularly interested in discovering modifiable risk factors for the cancer. Studies so far have identified smoking and long-standing diabetes as risk factors. But the role of diet remains unclear.

Some studies have found links between pancreatic cancer and high intakes of red meat and dietary fat, while others have failed to find such a relationship. Findings on carbohydrates and sugar have been similarly inconsistent.

Moreover, even when studies find an association between a diet pattern and a disease, that does not prove that the foods themselves are responsible for the increased risk.

For the current study, researchers led by Marta Rossi of the Mario Negri Institute for Pharmacological Research in Milan surveyed 326 pancreatic cancer patients about their health history and lifestyle, which included a detailed questionnaire on their diet habits in the two years prior to diagnosis.

Each patient was compared with two cancer-free adults the same age and sex.

Overall, Rossi’s team found, the one-third of participants with the highest-glycemic index diets were 78 percent more likely to have pancreatic cancer than the third with the lowest-glycemic index diets. The middle third fell in between, with a 56 percent higher risk.

The researchers then looked at certain select sources of carbohydrates, including fruit and a category that included sugar, candy, honey and jam. High intakes of the latter, it turned out, were linked to an increased risk of pancreatic cancer.

Rossi and her colleagues accounted for certain other factors, including participants’ weight, smoking history and any diabetes diagnoses - suggesting that higher rates of smoking, obesity or diabetes do not explain the link between pancreatic cancer and sugary diets.

Even if this link holds true in other studies, the absolute risk to any one person would be small.

According to the American Cancer Society, the average adult has just over a 1 percent chance of developing pancreatic cancer in his or her life. So even the 78 percent increase in that one percent risk linked to high-glycemic index diets in this study would translate into a small absolute risk for an individual.

The study does not show that sugary foods cause pancreatic cancer, but it is possible that such diets could contribute to pancreatic risk, according to the researchers. Even in the absence of diabetes, such foods influence the body’s secretion of the blood-sugar-regulating hormone insulin. And insulin encourages the growth and division of cells in the pancreas - raising the possibility that the hormone could encourage the growth and spread of pancreatic cancer cells.

More research is needed, however, to show whether this is the case, they write.

SOURCE:

Annals of Epidemiology, June 2010.