A long-running Swedish study involving more than 82,000 adults found no association between dietary nitrate and colorectal cancer, while men with the highest nitrite intake had a 23% higher risk, with the strongest association appearing in the distal colon.
By yourNEWS Media Newsroom.
A large Swedish study is drawing a sharper distinction between nitrate and nitrite after researchers found that the two compounds were not associated with colorectal cancer in the same way.
Researchers at Karolinska Institutet followed 82,009 middle-aged and older adults from two Swedish cohorts, combining detailed information about food and water consumption with national cancer records from 1998 through 2022.
During the study period, 3,170 participants developed colorectal cancer.
Nitrate consumption was not associated with an increased risk of the disease, researchers reported.
Nitrite produced a different result.
Among men, participants in the highest fifth of nitrite intake had a 23% higher risk of colorectal cancer than men in the lowest fifth. No corresponding association was detected among women.
The difference matters because nitrate and nitrite often appear together in discussions of food safety despite coming from different dietary sources.
Nitrate occurs naturally in soil and is absorbed by plants as they grow. Vegetables therefore account for much of the nitrate consumed in a typical diet.
Foods including spinach, beets, arugula and lettuce can contain substantial amounts of nitrate, yet researchers found no association between consumption of those nitrate-rich vegetables and colorectal cancer.
Nitrite is more commonly encountered as a preservative in processed meats.
Sodium nitrite is widely used in bacon, hot dogs, deli meats and other cured products because it limits bacterial growth while helping preserve color and extend shelf life.
Some pepperoni, salami and canned meat products can contain substantial amounts because curing depends heavily on nitrite. Certain plant-based deli products may also contain added nitrite to reproduce the color and preservation characteristics of conventional processed meat.
The distinction between nitrate and nitrite is not absolute because the human body naturally converts some dietary nitrate into nitrite.
Researchers nevertheless said the foods surrounding those compounds may influence what happens after they are consumed.
Vegetables typically supply vitamin C, polyphenols and fiber alongside nitrate. Those compounds can interfere with chemical reactions that form N-nitroso compounds in the digestive tract.
Processed meats generally do not provide the same combination of protective plant compounds.
N-nitroso compounds, including nitrosamines, have long been studied because some are carcinogenic. Toxicology research has described nitrosamines as compounds that can form during digestion involving sodium nitrate or sodium nitrite.
The Swedish study also found that the association involving nitrite was not evenly distributed throughout the large intestine.
Among men, higher nitrite intake was linked to a 50% greater risk of cancer in the distal colon, the portion of the colon nearest the rectum.
Researchers said that concentration of risk in a particular anatomical region could be consistent with a localized exposure effect.
Previous studies have similarly associated prolonged high consumption of red and processed meat with an elevated risk of cancer in the distal portion of the large intestine.
The sex difference was less easily explained.
Men showed the association between nitrite and colorectal cancer, while women did not.
Researchers identified several possible explanations but did not establish why the pattern differed by sex.
Men may consume processed meat differently or in greater quantities than women. Hormonal differences could potentially affect how N-nitroso compounds are processed in the digestive tract, while differences in sample size or statistical power could also contribute to the result.
Researchers said the finding requires additional study rather than assuming one biological explanation.
The results add to an existing body of evidence concerning processed meat and colorectal cancer.
The International Agency for Research on Cancer, part of the World Health Organization, has classified processed meat as carcinogenic to humans based on evidence linking its consumption to colorectal cancer.
The agency previously concluded that eating approximately 50 grams of processed meat each day was associated with an 18% increase in colorectal cancer risk.
That classification does not mean every person eating processed meat will develop cancer. It identifies evidence that the exposure can cause cancer, while individual risk depends on the quantity consumed and other factors.
Earlier research has also examined nitrate- and nitrite-containing processed meats in relation to other cancers.
One study linked consumption of certain cold cuts containing nitrate and nitrite with an almost 30% higher risk of bladder cancer. Researchers in that work noted that both compounds can act as precursors for N-nitroso compounds, some of which have produced tumors in multiple organs in experimental research.
The Karolinska findings nevertheless indicate that foods containing naturally occurring nitrate should not automatically be treated the same as processed foods containing added nitrite.
Spinach, lettuce, beets and arugula showed no association with colorectal cancer in the study despite being significant dietary nitrate sources.
Researchers instead pointed toward limiting processed meat as a more practical dietary approach.
The study characterized bacon, hot dogs, deli meats and heavily cured meats as leading sources of dietary nitrite and recommended treating processed meat as an occasional food rather than an everyday staple.
Vitamin C may also influence nitrite chemistry.
Because vitamin C can inhibit nitrosation, researchers noted that consuming foods rich in vitamin C alongside processed meat could potentially reduce formation of some N-nitroso compounds.
That possibility does not eliminate the broader risks associated with frequent processed-meat consumption, however, and the study did not establish that pairing processed meat with vitamin C prevents cancer.
The findings ultimately separate two substances that are often discussed as though they carry identical dietary risks.
Across more than two decades of observation involving 82,009 adults and 3,170 colorectal cancer diagnoses, researchers detected no relationship between nitrate intake and colorectal cancer.
The association appeared instead with nitrite: men consuming the highest amounts had a 23% higher colorectal cancer risk, while their risk of distal colon cancer was 50% higher than that of men with the lowest intake. No comparable association was found among women.
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