A new study suggests that consuming high amounts of nitrites, a preservative found in certain vegetables and processed meats, may increase the risk of bowel cancer by up to 50% in men. The World Health Organization classifies nitrites as a Group 1 carcinogen, placing them in the same category as tobacco and asbestos.
While concerns have largely focused on nitrites added to processed meats, such as bacon and ham, to extend shelf life and maintain color, this research indicates that the source of dietary nitrites may be less critical than previously understood. The study, published in the Journal of the National Cancer Institute, analyzed the dietary habits of over 82,000 middle-aged adults in Sweden over a 20-year period.
Participants completed food questionnaires, and researchers used data from the Swedish Food Agency along with their own measurements to estimate daily nitrite intake. During the follow-up, 3,170 individuals were diagnosed with colorectal cancer. The findings revealed that men with the highest nitrite intake were 23% more likely to be diagnosed with bowel cancer compared to those with the lowest intake. This association was particularly strong for cancers affecting the lower part of the bowel, where the increased risk reached 50%.
Notably, no significant association between nitrite intake and bowel cancer risk was observed in women. After adjusting for factors such as fiber intake, age, family history, weight, and smoking status, the researchers concluded that a diet high in nitrites elevates the risk of bowel cancer in men, irrespective of whether the nitrites originate from vegetables or meat products.
One theory suggests that the lower bowel may be particularly susceptible to harmful compounds formed when nitrites break down during digestion. Previous research has indicated higher levels of DNA damage linked to these compounds in this region of the bowel. However, the study authors emphasized that further research is needed to confirm these findings.
Bowel cancer is the fourth most common cancer in the UK and the second leading cause of cancer death, with over 17,000 lives lost annually. The disease is also reportedly the only cancer exclusively rising among those under 50 globally, with diagnoses in England among 25- to 49-year-olds increasing by over 50% since the early 1990s. Cancer Research UK estimates that more than half of all bowel cancer cases in Britain are preventable. Symptoms can include changes in bowel habits, blood in the stool, abdominal pain, bloating, unexpected weight loss, and fatigue.