Study details

For the study, researchers looked at data from the Korean National Health Insurance Service on over 6 million adults ages 20 to 39 who had no history of cancer and who underwent standardized national health screenings. On average, the researchers followed the participants for 11 years.

Body mass index (BMI) was categorized into five different groups ranging from underweight to class II obesity as defined by the World Health Organization's criteria for Asian populations.

The researchers also measured waist circumference as an indicator of abdominal adiposity, using the thresholds set by the Korean Society for the Study of Obesity, which put the waist circumference cutoff at over 90 cm (35.4 in) for males and over 85 cm (33.46 in) for females.

After adjusting for a variety of factors, including age, sex, smoking status, alcohol consumption, and metabolic comorbidities, the researchers found an increasing risk of cancer during the follow-up period based on obesity categories.

For example, 1.84% of those in the "normal weight" category developed some form of cancer during the follow-up period compared to 2.24% of those in the "class I obesity" category and 2.62% of those in the "class II obesity" category.

The researchers found the strongest associations between obesity and cancer risk for the following cancers:

• Colorectal
• Endometrial
• Kidney
• Liver
• Ovarian
• Pancreatic
• Thyroid

They did not find an association between obesity and the risk of developing breast cancer before the age of 50.

The researchers also found that waist circumference could be linked to cancer risk in a similar way to obesity.

Discussion

Previous research found similar associations between both obesity and waist circumference and cancer risk. One recent study suggested that 10% of the global burden of cancer could be attributed to overweight and obesity, and another study found an 11% potential increased risk of cancer in people with a waist circumference over established thresholds, even if they were physically active.

Patel noted that while the authors of the study reported smoking status, they did not report smoking intensity or duration, which could contribute to cancer risk.

Ketan Thanki, a board-certified colorectal surgeon with the MemorialCare Todd Cancer Institute at Long Beach Medical Center, said that obesity and cancer are linked because obesity causes states that promote cancer formation.

"Diet, exercise, and now medications can all be used very effectively to reduce one's weight and, hopefully as a result, cancer risk," Thanki said.

He also noted that, because of differences between the South Korean population and those elsewhere, further research will be needed to determine how well the study's results translate across other populations.

"But I think this trend will likely extend across all cultures," Patel said.