Men in the highest fifth of dietary nitrite intake had a 23 percent higher rate of colorectal cancer than men in the lowest fifth over two decades of follow-up, according to an analysis of 82,009 Swedish adults published in the Journal of the National Cancer Institute.
No such association appeared in women. Dietary nitrate, a related but distinct compound, showed no association with colorectal cancer in either sex.
The finding is an association observed in a population followed over time. It does not establish that nitrite caused these cancers, and nothing about current medical or dietary guidance changes because of it.
The Specific Result and Where It Concentrated
The researchers drew on two population-based cohorts, the Swedish Mammography Cohort and the Cohort of Swedish Men, tracking middle-aged and older adults over roughly 20 years.
Comparing the highest to the lowest quintiles of nitrite intake, men showed a hazard ratio of 1.23 with a statistically significant trend across quintiles. The signal was not spread evenly across the colon. In subsite analysis, nitrite intake was most strongly associated with distal colon cancer in men, with a hazard ratio of 1.50, as reported by Medscape. Proximal colon cancer carried a hazard ratio of 1.18 and rectal cancer 1.15, both with confidence intervals that crossed the point of no effect, meaning neither reached statistical significance.
One caution belongs with any subsite finding. When a single analysis is split into proximal colon, distal colon, and rectal cancer, and then split again by sex, the number of comparisons rises, and so does the chance that one of them clears statistical significance by chance alone. The distal colon result is the most striking number in the paper and also the one most exposed to that problem. It is a lead for further work rather than a conclusion.
The Chemistry Behind the Hypothesis
Nitrate and nitrite occur naturally in water, soil, and plants, and are also used as food additives, most prominently as preservatives in cured and processed meats.
The mechanistic concern is that nitrite can generate N-nitroso compounds in the body, several of which are established carcinogens in animals. Observational research has previously tied higher nitrite intake to gastric and esophageal cancers, and antioxidants can inhibit nitrosation reactions, which is why vitamin C intake is often examined alongside nitrite. The International Agency for Research on Cancer has classified ingested nitrate or nitrite under conditions resulting in endogenous nitrosation as probably carcinogenic to humans, a classification framed around the mechanism rather than the compound alone.
That framing matters for how a reader should interpret the source of nitrate in a diet. Vegetables rich in nitrate, such as spinach and lettuce, also contain protective antioxidants and vitamins, and this study found no association with dietary nitrate at all. The signal here is specific to nitrite.
The Contradictory Evidence That Belongs Alongside It
This result does not arrive in an empty field, and the prior literature has pointed in a different direction more often than not.
A systematic review and meta-analysis pooling 15 prospective cohort and case-control papers covering more than 2.5 million participants and 38,848 colorectal cancer cases found dietary nitrite not significantly associated with colorectal cancer, with a pooled hazard ratio of 1.07. That analysis did find a modest association for dietary nitrate, the opposite of the Swedish pattern.
The French NutriNet-Santé cohort reported elevated but non-significant hazard ratios for colorectal cancer with additive nitrites and nitrates, and attributed the null result partly to limited statistical power for that cancer site. A 27-year analysis of the Danish Diet, Cancer and Health Cohort, covering 54,610 participants and 2,245 colorectal cancer cases, found no association between colorectal cancer and nitrate or nitrite from plant sources, naturally occurring animal sources, or meat where the compounds are permitted as additives. That study did find an association between nitrate in tap water and distal colon cancer, a different exposure route entirely.
Set against that background, the Swedish result is a substantial addition rather than a settlement. Its strengths are duration and size. Its limitations are those common to all dietary cohort research: intake was estimated from food frequency questionnaires rather than measured, residual confounding cannot be excluded, and a single-country cohort may not generalize.
The sex difference is genuinely unexplained. The authors reported it as observed rather than offering a confirmed mechanism, and readers should treat it that way.
The Practical Takeaway for a Reader Deciding Anything
Nothing about screening changes because of this paper. Colorectal cancer screening recommendations are based on age and personal and family risk, and most guidelines in the United States begin at 45 for average-risk adults. Anyone eligible who has not been screened has a far larger opportunity to reduce risk than any adjustment to nitrite intake would offer.
Established colorectal cancer risk factors remain what they were: age, family history, inflammatory bowel disease, smoking, heavy alcohol use, obesity and physical inactivity, alongside processed meat consumption, which the International Agency for Research on Cancer has classified as carcinogenic to humans based on a much larger body of evidence than this single study.
Anyone considering a change to their diet should discuss it with a clinician or registered dietitian who knows their history, rather than acting on a single observational finding. This article describes research, not individualized advice.
What remains unresolved is why the association appeared only in men, why it concentrated in the distal colon, and whether the finding replicates elsewhere. Confirmation would require similar analyses in cohorts outside Sweden, ideally in populations with different processed meat consumption patterns and different baseline colorectal cancer rates.
Key Questions Answered
What did the study find? Men in the highest fifth of dietary nitrite intake had a 23 percent higher rate of colorectal cancer than those in the lowest fifth. No association was found in women, and none was found for dietary nitrate in either sex.
How large and long was it? 82,009 middle-aged and older Swedish adults from two population-based cohorts were followed over roughly 20 years.
Does this prove that nitrite causes colorectal cancer? No. This is an observational association. Intake was estimated from questionnaires, and residual confounding cannot be excluded.
Where was the association strongest? Distal colon cancer in men, with a hazard ratio of 1.50. Estimates for proximal colon and rectal cancer were elevated but not statistically significant.
Do other studies agree? Not consistently. A meta-analysis of 15 studies found no significant association between dietary nitrite and colorectal cancer, and a 27-year Danish cohort found no association between nitrite from food sources and colorectal cancer.
Should I stop eating vegetables high in nitrates? The study found no association with dietary nitrate. Questions about individual diets should be directed to a clinician or registered dietitian.
Has medical guidance changed? No. Screening recommendations and established risk factors are unchanged.
