High-vegetable Diet Linked To Protection Against Pancreatic Cancer

The vegetables most strongly associated with increased protectionwere onions, garlic, beans, yellow vegetables (such as carrots, yams,sweet potatoes, corn and yellow squash), dark leafy vegetables andcruciferous vegetables. Light-green vegetables, tomatoes and tomatoproducts showed weaker protective benefits.

Fruits were found to be protective but significantly less so thanvegetables, with citrus fruits and citrus juices most protective.

The 50 percent reduced risk was associated with eating at last fiveservings per day of the protective vegetables or vegetables and fruit,compared to those who ate two servings a day or less. And eating nineservings per day of vegetables and fruit combined also was associatedwith about a 50 percent reduced pancreatic cancer risk compared witheating less than five servings per day. A serving is considered to beabout a half cup of cooked vegetables, two cups of leafy salad or onemedium-sized piece of fruit.

The study was based on in-person interviews of 2,233 San Francisco BayArea residents: 532 pancreatic cancer patients and more than 1,700randomly selected "controls." Control group participants did not havepancreatic cancer but were of a similar age distribution and similarmale to female ratio as the pancreatic cancer patients. Participantswere asked about their fruit and vegetable consumption for the one-yearperiod prior to the interview, as well as other questions about diet,smoking, occupation and other factors.

The study findings regarding fruit and vegetable consumption are beingpublished in the September issue of the journal Cancer, Epidemiology,Biomarkers and Prevention."Pancreatic cancer is not nearly as common as breast or lung cancer,but its diagnosis and treatment are particularly difficult," saidElizabeth A. Holly, PhD, UCSF professor of epidemiology andbiostatistics and senior author of the study. "Finding strongconfirmation that simple life choices can provide significantprotection from pancreatic cancer may be one of the most practical waysto reduce the incidence of this dreadful disease."

The results are considered particularly meaningful because of thestudy's size, the quantitative nature of the food questionnaire and thestatistical significance of the findings, according to the study team.The likelihood that chance alone accounts for the discoveredcorrelations between diet and cancer is less than one in a thousand formany vegetable categories, and well within the limits consideredstatistically significant for most of the vegetables studied, thescientists reported.

The findings don't necessarily mean that all fruits and vegetables --or any specific ones -- are potentially helpful or harmful, the authorspoint out. For example, they found evidence that the way foods areprepared may play a role: raw vegetables appear to be somewhat moreprotective than cooked vegetables, and fried potatoes appear to be moreharmful than those prepared other ways. In addition, a specific foodcould be a "proxy" for another food that is often eaten with it, suchas meat eaten with fried potatoes, for a hypothetical example.California physicians are required by law to report all cancer cases toa statewide records center, which allowed the researchers to identifyall pancreatic cancer patients treated within a five-year period in sixBay Areas counties: Alameda, Contra Costa, Marin, San Francisco, SanMateo and Santa Clara.

The research approach used by the UCSF team is called a "case-control"study because it involves a comparison of pancreatic cancer cases witha control group without pancreatic cancer. The main limitation of thisapproach is that many of the cancer patients identified at the outsetdie before they can be interviewed, as was the case with the UCSFstudy, the researchers reported.

Still, the alternative research approach -- a "prospective"study that inquires about diet and then follows people long enough todetermine which of them contracts the disease -- is less feasiblebecause it requires a very large sample size and a very long follow-upperiod, since pancreatic cancer is relatively rare, Holly said.

The authors note that a few prospective cohort studies have publishedresults looking at fruit and vegetable consumption in relation topancreatic cancer risk, and have observed no association or possibly aslight suggestion of benefit. This may be due, in part, to the reducednumber of cancer cases available in such a study design, Hollysuggested.

"With more follow-up, such studies will be able to examine thisquestion more rigorously," said June M. Chan, ScD, assistant professorof epidemiology and biostatistics at UCSF and lead author of the paper."In the meantime, results from case-control studies like this oneprovide support for the hypothesis that vegetables and fruit providesome benefit in protecting against the development of pancreaticcancer."

The researchers previously reported on other findings from thisin-person interview-based study, namely: allergies, obesity, clinicalsymptoms of pancreatic cancer and environmental factors in relation topancreatic cancer; also, genetic factors in relation to pancreaticcancer and cigarette use. Other factors still to be examined in thisstudy are the relationship between pancreatic cancer an alcohol,detailed analyses on cigarette use, diet, other diseases andconditions.

Co-author on the paper with Holly and Chan is Furong Wang, MD, senior statistician in epidemiology and biostatistics at UCSF.

The research was supported by the National Cancer Institute. This paperwas partially supported by the Rombauer Pancreatic Research Fund.