No Strong Link Between Nitrates and Pancreatic Cancer

Animal studies have shown that dietary inclusions of items that contain “nitrates” and “nitrites” are linked to pancreatic cancer. This study attempted to see if a similar relationship exists in humans. A total of 1,728 cases of pancreatic cancer were detected in the study population that was followed up for 10 years. Participants answered a food questionnaire that showed no relation of nitrates and nitrites with pancreatic cancer. However, men who ate more processed meat were at a slightly increased risk for pancreatic cancer. Women were not at a similar risk.

Pancreatic cancer has been found to be the fourth largest killing cancer among Americans, and causes 5 percent of all cancer-related deaths. Some well-defined risk factors cause a predisposition to pancreatic cancer, notably obesity, diabetes, and smoking.  Most of these associations are yet unclear as this cancer’s pathology remains ill-defined. Diet also seems to play a role in causing pancreatic cancer. In animal studies, it is seen that nitrates and nitrites in the diet lead to the formation of “N-nitroso compounds or NOCs” that can facilitate the formation of pancreatic tumors in them. However, there are no long-term large studies that show a similar association in humans. This study attempted to explore this association. Nitrates are found naturally in high quantities in leafy vegetables like spinach and lettuce, and also in beets.

* Participants, aged between 50 and 71, were selected from the general population residing in six states – Florida, California, New Jersey, Pennsylvania, Louisiana and North Carolina and two metropolitan regions – Atlanta, Georgia, and Detroit, Michigan.
* All participants were sent a questionnaire that asked them about their food habits over the past one year. After six months of this questioning, they were again sent a questionnaire that recorded their quantity and type of meat intake.
* At the end of the study, the number of participants who had answered the food questionnaire was 198,735 females and 293,491 males. Those that answered the meat questionnaire were 126,314 females and 176,842 males.

Key findings
* In the 10 years of follow-up of the study population, 1,728 new cases of pancreatic cancer were detected.
* The average dietary nitrate intake for the group of participants was 88 mg per day, and the average intake of nitrite was 1.2 mg per day. For men, the average of combined intakes of nitrate and nitrite from processed meat sources was 1.3 mg per day among men; and for women, 0.8 mg per day. Women consumed less processed red and white meat than men.
* There was no risk of pancreatic cancer associated with high intakes of nitrates and nitrites.
* However, men who ate the highest amounts of processed meats had a slightly raised risk of getting pancreatic cancer with odds of 1.18. The risk was a bit higher if men ate processed meats from 12 or 13 years of age with odds of 1.32. Women did not show a similar risk.

Next steps/shortcomings
The authors of this study write that, in their results, women could have appeared to be at a lower risk of pancreatic cancer from consuming processed meat intake due to their misreporting more than men. They admit that women may have reported diet habits that they perceived as healthy instead of their actual habits. Further studies in this respect are necessary.

This study included a large population that was followed for nearly a decade. No actual relation between nitrate and nitrite intake in diet and pancreatic cancer was found. There was, however, a marginally higher risk of the cancer in men who ate more processed meats, especially if they ate it during their teenage years.  The authors speculate that since it is difficult to regularly screen or detect pancreatic cancer at early stages, this study is vitally important. In many cases, the cancer is detected late and surgery also fails to increase survival. The authors write, “…therefore, the identification of preventable exposures such as dietary factors is an important area of investigation.”

For More Information:
Pancreatic Cancer and Exposure to Dietary Nitrate and Nitrite in the NIH-AARP Diet and Health Study
Publication Journal: American Journal of Epidemiology, June 2011
By Briseis Aschebrook-Kilfoy; Amanda J. Cross; National Cancer Institute, Bethesda, Maryland

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