A recent study indicates that consuming high quantities of nitrites, a compound present in leafy green vegetables such as rocket and swiss chard, could increase the risk of developing bowel cancer by as much as 50% in men. The World Health Organization classifies nitrites as a Group 1 carcinogen, a designation shared with substances like tobacco and asbestos.
While concerns have historically centered on nitrites added to processed meats as preservatives, the new research suggests that the source of dietary nitrites may be less significant than previously believed. 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 in 1997, 2009, and 2019, and individuals with prior cancer diagnoses (excluding non-melanoma skin cancer) were removed from the analysis.
Researchers utilized data from the Swedish Food Agency and their own measurements of nitrites in various foods to estimate participants' average daily intake. Over the follow-up, 3,170 participants 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. No significant association 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 the food source. The association was particularly strong for cancers affecting the lower part of the bowel, where men with the highest nitrite consumption faced a 50% increased risk. One hypothesis suggests this region of the bowel may be more susceptible to harmful compounds formed during the digestion of nitrites, as previous studies have indicated higher levels of DNA damage linked to these compounds in this area.
Bowel cancer is a significant health concern, being the fourth most common cancer in the UK and the second leading cause of cancer deaths, accounting for over 17,000 lives annually. Alarmingly, it is also the only cancer with rising exclusively among individuals under 50 globally. In England, diagnoses among those aged 25 to 49 have increased 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, abdominal pain, unexplained weight loss, and fatigue.