An Onion a Day May Repel Pancreatic Cancer

October 4, 2007

NUTHETAL, Germany -- An onion a day may help fend off pancreatic cancer, but apples were a bust, found investigators studying the cancer-fighting role of flavonols.

NUTHETAL, Germany, Oct. 4 -- An onion a day may help fend off pancreatic cancer, researchers here said.

Apples, on the other hand, may not, Ute Nthlings, Ph.D., of the German Institute of Human Nutrition Potsdam-Rehbruecke, and colleagues in California and Hawaii, reported in the October issue of the American Journal of Epidemiology.

The finding comes from the Multiethnic Cohort Study, which collected baseline data -- including dietary information -- on more than 215,000 people ages 45 to 75 from 1993 through 1996 in California and Hawaii, said Dr. Nthlings and colleagues.

For this analysis, the researchers looked at possible links between flavonols -- a class of polyphenols found in fruits and vegetables and thought to have cancer-fighting properties -- and the risk of pancreatic cancer.

Data were available on 183,518 participants, Dr. Nthlings and colleagues reported. Among those, during eight years of follow-up, there were 529 cases of exocrine pancreatic cancer.

Dr. Nthlings and colleagues examined consumption of three flavonols -- quercetin, most abundant in onions and apples; kaempferol, found in spinach and some cabbages; and myricetin, found mostly in red onions and berries -- as well as the total flavonol intake.

The bottom line was that total flavonol consumption was associated with a lower risk of pancreatic cancer: When the researchers compared the lowest quintile of total intake to the highest, the relative risk was 0.77, and the trend was significant at P=0.046.

But some foods appeared to be better than others, the researchers said.

Onions and black tea appeared to show "modest inverse associations" with pancreatic cancer, although the trends were not significant (P=0.056 and P=0.07, respectively), the researchers said.

Apples and green, herbal, or other teas, on the other hand, showed no such associations.

A Cox regression analysis showed that kaempferol was associated with a significant reduction in cancer risk. When the lowest and highest quintile were compared, the relative risk reduction was 0.78, and the trend was significant at P=0.017.

Neither quercetin nor myricetin was associated with a reduced risk in the overall cohort.

On the other hand, among smokers total consumption and each of the flavonols individually was associated with reduced risk. When the lowest and highest quintiles were compared:

  • Total consumption was associated with a relative risk reduction of 0.41, and the trend was significant at P=0.002.
  • Quercetin consumption was associated with a relative risk reduction of 0.55, and the trend was significant at P=0.008.
  • Kaempferol was associated with a relative risk reduction of 0.27, and the trend was significant at P<0.0008.
  • And myricetin was associated with a relative risk reduction of 0.55, and the trend was significant at P=0.044.

"The effect was largest in smokers, presumably because they are at increased pancreatic cancer risk already," Dr. Nthlings said at the American Association for Cancer Research meeting in April, where some of the data was presented.

Smoking is the only established risk factor for pancreatic cancer, Dr. Nthlings said.

The study is limited because "some degree of measurement error in the estimation of flavonol intake was certainly present," the researchers said. But the questionnaire used was designed to capture a range of foods and mixed dishes, which may reduce the error, they added.

Dr. Nthlings and colleagues said similar studies are needed in other groups and regions of the world to confirm the findings.