The evidence that prolonged inflammation can cause or promote cancer is consistent and points in the same direction, although it is largely based on observational and mechanistic research without large randomised trials on cancer outcomes. The strongest association exists with chronic bowel diseases and obesity. In practical terms, this means that reducing chronic inflammation through lifestyle is a meaningful preventive strategy.
Prolonged, low-grade inflammation in the body is a recognised cause of cancer. A large review article1 shows that chronic inflammation, fuelled by social, environmental and lifestyle factors, makes cancer one of the most common consequences worldwide. This is not the acute inflammation you feel with a wound or infection, but a smouldering, persistent state in which the immune system remains active for years, thereby creating the environment in which cancer cells can arise and grow.
In obesity, the mechanism has been studied most concretely. Adipose tissue becomes chronically inflamed and behaves like continuously damaged tissue, full of infiltrating immune cells. This leads to increased production of inflammatory substances such as TNF-alpha, IL-6 and IL-1beta, which drive insulin resistance and oxidative stress. Epidemiological research shows strong associations between obesity and breast, colorectal, liver and pancreatic cancer2,3. Notably, this adipose tissue inflammation also occurs in some people with a normal body weight, so weight alone is not a sufficient measure of risk.
Another well-documented example is chronic intestinal inflammation in diseases such as ulcerative colitis and Crohn's disease. The persistent inflammation in the intestinal wall alters the local cellular environment so profoundly that tumour formation is promoted, increasing the risk of colorectal cancer4. This is also one of the reasons why people with inflammatory bowel diseases are monitored particularly closely by their doctor.
Chronic inflammation also links cancer to cardiovascular disease. Shared risk factors such as obesity and diabetes fuel the same inflammatory mechanism, causing both conditions to frequently occur together5. This is an associative relationship and not yet proof that one disease causes the other, but it does underline that addressing chronic inflammation can yield broad health benefits.
An epidemiological association has also been found between chronic gum inflammation (periodontitis) and cancer. Animal experiments and intervention studies point to a biologically plausible pathway via systemic inflammation, but convincing evidence in humans is still lacking6. This association is interesting but calls for caution in interpretation.
The good news is that adipose tissue inflammation is reversible. Weight loss through diet and increased physical activity has been shown to significantly reduce cancer risk, presumably precisely because chronic inflammation decreases2,3. No exact percentages are given, but the direction is clearly positive. Anyone who improves their lifestyle by eating more healthily, exercising more and paying attention to their weight reduces a proven risk factor for cancer.
Based on multiple review and overview articles (PMID 31806905, 27903155, 40714142, 39465427, 26976915, 33510490). The strength of evidence varies by cancer type and exposure factor: strong for the general SCI-cancer link and IBD-related colorectal cancer, moderate for obesity-related cancers, limited for periodontitis. Specific risk figures are not provided in the sources. No randomised trials on long-term cancer outcomes are available in this source selection.