Does eating a lot of sugar increase my risk of cancer?
There are clear indications that regularly drinking sugar-sweetened beverages raises the risk of liver cancer in particular, but a proven causal relationship has not yet been established. Limiting sugar-sweetened beverages is sensible, even though the science has not yet reached a definitive conclusion.
Sugar-sweetened beverages are the best-studied part of this question. A large study of more than 90,000 postmenopausal women, followed for nearly 21 years, showed that drinking one or more glasses of sugar-sweetened beverages per day was associated with an 85% higher risk of liver cancer and a 68% higher risk of dying from chronic liver disease, compared with women who rarely drank such beverages. This is an observational association: other lifestyle factors may also play a role, and causality has not been proven. But the finding is strikingly large and was observed in a long-running, large-scale study.
A broad review article confirms that there is considerable evidence for a link between regular consumption of sugar-sweetened beverages and a higher risk of certain cancers. Which cancer types are most strongly involved varies from study to study. Early-onset colorectal cancer (under age 50) is also linked, in a separate review, to a Western diet rich in refined carbohydrates and high-fructose syrup, although that involves a combination of dietary factors rather than sugar alone.
Why sugar might contribute to cancer has not yet been firmly proven in humans. Laboratory research suggests that a high sugar intake causes chronic low-grade inflammation and disrupts the immune system, potentially making it less effective at clearing cancer cells. This is mechanistic reasoning and does not yet count as clinical evidence.
Artificially sweetened beverages showed no significantly elevated risk in the liver cancer study. A separate meta-analysis of 25 studies involving nearly 3.7 million participants also found no clear association with cancer in general, apart from a small increase in European studies. That small increase may be explained by other dietary habits. Artificial sweeteners are therefore not a demonstrably safe alternative in every respect, but for cancer specifically there is currently no strong evidence of harm.
All claims are based on observational research (cohort studies, meta-analyses of cohort studies, and review articles). No randomised controlled trials are available for this question. Causality cannot be established. The liver cancer finding applies only to postmenopausal women and cannot be directly generalised to men or younger women.