Impact of overweight on cancer risk may be significantly underestimated

Being overweight and obesity may contribute to significantly more cancer cases than previously thought. This is the conclusion reached by researchers at the German Cancer Research Center (DKFZ). Their analysis shows that when more accurate measures of body fat and methodological biases are considered, more than 10% of all cancer cases can be attributed to increased body weight—nearly twice as many as previous estimates suggested.

Overweight and, in particular, obesity are known cancer risk factors. Previous studies have estimated that they account for about 2% to 8% of all cancer cases. However, Hermann Brenner, an epidemiologist at the DKFZ, has long suspected that this proportion may have been underestimated because of methodological biases. Together with his team, he analyzed data from 458,543 women and men in the UK Biobank to investigate the links between being overweight and cancer.

The participants were followed for a median of nearly 12 years. During this period, more than 50,000 new cancer cases occurred. The research is published in the journal Cancer Communications.

Weight and height alone are not enough

Most studies on obesity and cancer have relied on body mass index (BMI), which is calculated from weight and height. However, BMI does not distinguish between fat and muscle mass and provides no information about where fat accumulates in the body. Yet abdominal fat, in particular, is metabolically active and closely linked to inflammatory processes and other mechanisms that can promote cancer.

The DKFZ researchers therefore compared not only BMI but also waist circumference and the waist-to-hip ratio as measures of fat distribution. These parameters proved significantly more informative regarding cancer risk.

Methodological bias: Cancer often leads to weight loss before diagnosis

In their current study, Brenner and his team also addressed a previously underestimated methodological issue: Many tumors cause unintentional weight loss years before they are diagnosed. As a result, patients appear slimmer at the time of diagnosis, weakening the statistical link between obesity and cancer.

To avoid potential biases caused by weight loss before diagnosis, the researchers gradually excluded the first few years following the participants’ enrollment in the study. This made the association much clearer. A significant proportion of cancers diagnosed during the first few years of follow-up were likely already present at the start of the study and had already led to weight loss in those affected.

More than 10% of all cancer cases could be preventable

In summary, the new analyses yielded significantly higher figures for the proportion of all cancer cases attributable to obesity. Considering all methodological improvements in the analyses, the estimated proportion of cancer cases caused by excess weight rose from about 5.5% to as high as 11.5%. This means that more than 1 in 10 cases could be linked to excess body fat.

Women appear to be more affected

The analyses also suggest that the proportion of cancer cases caused by obesity may be higher among women than among men. Body fat may also tend to play a greater role among adults younger than 60.

According to Brenner, the results underscore the urgency of taking decisive action to counter the global rise in obesity. “Since the prevalence of obesity continues to rise in most countries and the population is aging at the same time, the number of cancer cases caused by obesity is likely to continue to rise significantly in the future. Effective strategies for the prevention and treatment of obesity could therefore make a much greater contribution to cancer prevention than previously assumed,” Brenner said, summarizing the significance of the new findings.

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Gaby Clark

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Andrew Zinin

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