Being obese or overweight can increase the odds of developing several types of cancers, new research from the United Kingdom reveals.
But shedding the excess pounds can lower the risk, researchers say.
Reducing obesity cuts the risk for endometrial cancer by 44% and uterine cancer by 39%, and could also prevent 18% of kidney cancers and 17% of stomach and liver cancers, according to the study.
"It all depends on keeping the weight off," said lead researcher Carlos Celis-Morales of the BHF Institute of Cardiovascular and Medical Sciences at the University of Glasgow in Scotland. He noted that many people lose weight only to regain it back -- and then some.
"What we need is kind of a long-term healthy weight and people that achieve that will reduce the risk," Celis-Morales said. "That is why it's so important that people improve the quality of their lifestyle in order to keep a healthy body weight."
He cautioned, however, that this study can't prove that excess weight causes cancer or that losing weight prevents it, only that there seems to be a strong connection between excess weight and cancer risk.
For the study, Celis-Morales and his colleagues drew on data from the U.K. Biobank on more than 400,000 men and women who were cancer-free.
The investigators wanted to know the risk of developing and dying from 24 cancers based on six markers of obesity: body fat percentage, waist-to-hip ratio, waist-to-height ratio, waist and hip circumferences and body mass index (BMI), an estimate of body fat based on height and weight.
No matter which way it was measured, obesity increased the odds of developing 10 of the most common cancers, the study found. A larger waist and hips, BMI or percentage of body fat all provided similar cancer risk.
Celis-Morales said BMI is an adequate way to gauge weight-related cancer risk, and there's no benefit in turning to more complex or costly measures such as waist size or body fat percentage.
For example, a BMI score of 24.9 is considered normal, and every addition of about 4 for men and 5 for women above 25 was linked a 3% higher risk of cancer overall.
It also increased the risk of cancers of the stomach (35%), gallbladder (33%), liver (27%), kidney (26%), pancreas (12%), colon (10%), and bladder (9%).
That same amount of excess weight was also associated with a sharply higher odds of two cancers affecting women -- 73% for endometrial cancer and 68% for uterine cancer. It also was linked to an 8% increase for postmenopausal breast cancer.
Lauren Teras, scientific director for epidemiology research at the American Cancer Society, reviewed the findings.
"Some of the ways in which obesity is thought to impact cancer includes elevated levels of sex hormones such as estrogen and progesterone, also insulin-related growth factors and leptin and adiponectin, which are proteins given off by fat tissue," she said.
Despite strong evidence that excess weight boosts risk for many cancers, less is known about whether losing weight can successfully reverse it, Teras said.
"This is likely because losing weight in adulthood is relatively uncommon, making it difficult to study," she said. "However, several studies of patients undergoing major weight-loss surgeries have found lower risk of several types of cancer in these patients."
Maintaining a normal weight, eating a balanced diet and being physically active are beneficial for many aspects of health, Teras said.
"My advice is to find a plan that works for you and stick with it until it becomes a habit," she suggested. "To increase your physical activity, do what sounds fun to you. Eat a diet that is customized to your preferences, but includes fruits, vegetables and whole grains. Limit portion sizes."
Then find an accountability partner to keep you on track. "We're all more likely to succeed when we have support," Teras said.
The findings were published May 9 in the journal BMC Medicine.
For more on cancer and weight, see the American Cancer Society.
SOURCES: Carlos Celis-Morales, PhD, research fellow, BHF Institute of Cardiovascular and Medical Sciences, University of Glasgow, Scotland; Lauren Teras, PhD, scientific director, epidemiology research, American Cancer Society; BMC Medicine, May 9, 2021