Written by Charles Bankhead
“The risk of pancreatic cancer declined significantly as intake of antioxidants increased among participants in a large case-control study.
The magnitude of risk reduction varied by the quantity and types of antioxidants but reached a maximum of 67% in people who had the greatest intake of vitamins C and E and selenium.
The data suggested a threshold effect for selenium and a trend toward a threshold effect for vitamin E, as well as a significant inverse association between pancreatic cancer risk and serum levels of vitamin C.
‘The results support measuring antioxidants in studies investigating the etiology of pancreatic cancer,” Andrew R. Hart, MD, of the University of East Anglia in Norwich, and co-authors wrote in conclusion in an article published online inÂ Gut. “If the association is causal, one in 12 cancers might be prevented by avoiding the lowest intakes (of antioxidants).’
Most patients with pancreatic cancer have a poor prognosis, owing in large part to late diagnosis and poor understanding of the disease’s etiology. Factors associated with an increased pancreatic cancer include a family history of the disease, smoking, type 2 diabetes, chronic pancreatitis, andHelicobacter pyloriÂ infection, according to background information in the article.
Pancreatic cancer risk has an inverse association with use of aspirin and statins, however, and dietary factors might also influence the risk. In particular, several plausible biological mechanisms suggest a possible role for antioxidants in the cancer risk. But the few cohort studies that have examined associations have produced mixed results.
Hart and colleagues undertook a study to evaluate links between antioxidant intake and pancreatic cancer risk on the basis of data from 7-day food diaries. They study involved 23,658 participants in the European Prospective Investigation of Cancer (EPIC) Norfolk Study, which spanned the years 1993 to 1997.
Study participants were enrolled from 35 general medical practices in Norfolk County, England. The cohort comprised men and women ages 40 to 74 at the time of enrollment.
Each participant had a baseline physical examination, during which blood samples were drawn. Additionally, study nurses explained how to complete the 7-day food diary. Completed diaries were evaluated and coded by trained nutritionists.
EPIC-Norfolk participants were followed to June 2010, and new diagnoses of pancreatic cancer were identified from regional health authority records and a cancer registry. Participants were excluded from the cancer analysis if uncertainty existed about the diagnosis, if the cancer was present at enrollment, or if the diagnosis occurred during the first year of follow-up.
Investigators determined that 49 EPIC-Norfolk participants developed pancreatic cancer during follow-up. The patients were compared with a control group of 3,970 participants who did not have pancreatic cancer.
Patients and the control group were separated into quartiles of intake for vitamin C, vitamin E, selenium, and zinc. Those who were in the highest three quartiles for each of vitamins C and E and selenium had a 67% reduction in the hazard for pancreatic cancer as compared with participants in the lowest quartile (HR 0.33, 95% CI 0.13 to 0.84,Â P<0.05).
Among the individual antioxidant nutrients, a significant threshold effect (quartiles 2 through 4 versus quartile 1) was seen for selenium (HR 0.49, 95% CI 0.26 to 0.93,Â P<0.05), and a trend was evident for vitamin E (HR 0.57, 95% CI 0.29 to 1.09). With the exception of zinc, individual quartiles (2 through 4 versus 1) of antioxidant intake were less than 1.
Serum levels of vitamin C had a significant inverse association with pancreatic cancer risk (HR 0.67, 95% CI 0.49 to 0.91,Â P=0.01), but not a threshold effect of intake as determined by 7-day food diaries (HR 0.68, 95% CI 0.37 to 1.26).
“The current evidence from etiological epidemiological work is minimal and inconsistent, although our work using an accurate method of dietary assessment and other studies using biomarkers of antioxidants suggest that vitamins C and E and selenium may be protective,” the authors wrote in conclusion.
‘While null results from dietary antioxidant supplementation trials for other cancer endpoints have been discouraging, food sources of these nutrients may have different effects from high-dose single supplements.’”