Carrying extra body weight has long been linked to a higher risk of several types of cancer. Scientists have known about this connection for many years, but exactly how much obesity contributes to cancer has remained uncertain.
A new study from the German Cancer Research Center (DKFZ) now suggests that the impact of excess body fat may be much greater than experts once believed. The research was published in the journal Cancer Communications.
Earlier studies estimated that excess weight was responsible for about 2% to 8% of cancer cases. However, the new analysis suggests that more than one in every ten cancer cases may be linked to overweight and obesity. If confirmed, this means the role of obesity in cancer has been seriously underestimated.
The research team, led by epidemiologist Hermann Brenner, examined health information from 458,543 men and women taking part in the UK Biobank. Participants were followed for almost 12 years on average, during which more than 50,000 people developed cancer. The large number of participants allowed researchers to study long-term patterns with greater confidence.
Most previous studies relied on body mass index, or BMI, to measure body weight. BMI is calculated using height and weight, but it cannot tell the difference between body fat and muscle. It also cannot show where fat is stored, even though fat around the waist is known to be more harmful than fat stored elsewhere.
The researchers therefore looked at waist size and the waist-to-hip ratio as well as BMI. These measurements gave a clearer picture of body fat and proved to be better at predicting cancer risk. Belly fat is especially active inside the body and can promote long-term inflammation, hormone changes, and other processes that may encourage cancer to develop.
The team also addressed another important problem that may have distorted earlier studies. Many cancers cause people to lose weight long before they are diagnosed. As a result, some people who already had undetected cancer appeared slimmer when they entered previous studies, making obesity seem less strongly linked to cancer.
To reduce this problem, the researchers excluded cancers diagnosed during the first few years after volunteers joined the study. This helped remove people who were probably already developing cancer when the research began. Once these cases were excluded, the relationship between obesity and cancer became much stronger.
The updated analysis estimated that about 11.5% of all cancer cases could be linked to excess body fat. Women appeared to be affected more than men, and obesity seemed to play an even larger role in adults younger than 60 years. These findings suggest that preventing obesity could have a greater effect on reducing cancer than previously thought.
The study does not prove that obesity directly caused every cancer case because it was an observational study. Even so, its large size and improved methods strengthen confidence in the results. Future studies in other populations will help confirm whether the findings apply worldwide.
In review, this research provides a more accurate picture of how excess body fat may influence cancer risk. By using better measures of body fat and correcting an important source of bias, the scientists found a much stronger association than earlier reports.
The findings support continued efforts to promote healthy eating, regular physical activity, and weight management as important ways to lower future cancer risk.
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Source: German Cancer Research Center (DKFZ).
