Being overweight before age 40 increases cancer risk
A new study shows that excess weight in adulthood increases women’s risk of endometrial cancer, while in men the increased risk was in kidney and colon cancer.
Obesity is a known risk factor for many cancers. Now, researchers have also found that the timing of when you become overweight can affect your cancer risk.
“Our study confirms that weight gain in adulthood increases the risk of cancer. Being overweight before age 40 increases the risk of obesity-related cancer by 16 per cent for men and 15 per cent for women,” says Tone Bjørge, the lead scientist behind the new study and professor at the Department of Global Public Health and Primary Care at the University of Bergen.
The researchers conducted an epidemiological study, in which they studied different population groups. In this study, researchers relied on data from more than 220,000 people from Norway, Austria and Sweden.
All of the people considered for the study had previously participated in health surveys where their BMI was measured on at least two occasions. The researchers then looked at how many of these people later got cancer. They were specifically interested in people who became overweight before age 40.
Significantly increased risk of endometrial cancer
Previous research has shown that being overweight increases the risk of several types of cancer, including colon cancer, rectal cancer, kidney cancer, uterine cancer and post-menopausal breast cancer.
The recent study shows that for women who became overweight before they were 40, the risk of endometrial cancer increased by as much as 70 per cent, compared to those who were not overweight before they turned 40.
For men, there was an increase in risk of renal cell cancer— a type of kidney cancer — and bowel cancer. Overweight men had a 58 per cent higher risk of getting this type of kidney cancer, and a 29 per cent higher risk of getting colon cancer.
The study found no association between being overweight and cancers not previously thought to be linked to obesity.
Weight gain of five kilos up increased risk
The study also shows that the risk of being affected by cancer increases the greater the weight gain and the higher a person’s BMI.
“We had access to data from large health registers, and could look at many types of cancer. The results are slightly different for the different cancers,” says Bjørge.
A weight gain of five kilos led to an increased risk of all types of obesity-related cancer for women.
Men who were obese, or who had a BMI over 30 at the first two measurements had a 64 per cent higher risk of getting obesity-related cancer compared to men who were normal weight.
Various factors affect cancer risk
There are likely complex reasons why some types of cancer are affected by being overweight.
“Slightly different mechanisms probably have an effect on different cancers. Sex hormones, growth factors and underlying inflammatory conditions are factors associated with being overweight. These in turn probably affect different cancers to varying degrees,” says Bjørge.
However, the risk of breast cancer does not appear to be affected by being overweight at a young age.
“Here the picture is a little different — in fact, it seems that obesity reduces the risk of breast cancer before menopause, while obesity increases the risk of breast cancer after menopause,” says Bjørge.
The researchers note in the study that an increasing number of people are overweight, which will have major consequences for public health — partly because of the increased cancer risk.
“If you manage to maintain a normal weight, you are at lower risk of many cancers. Avoiding obesity is preventative! This of interest, because weight is something that you can control to a certain extent,” says Bjørge.
Authorities need to do more
Bård Kulseng, head of the Centre for Obesity Research and Innovation and a head physician at St. Olavs Hospital in Trondheim, says the study confirms that the risk of cancer increases when people are overweight.
“More and more research in recent years has suggested this. Now, when fewer people smoke, it appears that obesity may be the most important risk factor for cancer that you can actually do something about,” says Kulseng.
He believes that health authorities must do more to counteract the trend for people to be overweight.
“Being overweight has such significance for public health that authorities should campaign against it. The fight against being overweight is just as important as the fight against traffic deaths and smoking,” says Kulseng.
Tone Bjørge et al.: BMI and weight changes and risk of obesity-related cancers: a pooled European cohort study, International Journal of Epidemiology, September 2019