Researchers at the Daffodil Center, a joint venture of Cancer Council NSW and the University of Sydney, have reported that the rate of obesity-related cancers in Australia almost quadrupled between 1983 and 2017, foreshadowing a growing preventable cancer crisis unless urgent steps are taken to reverse Australia's obesity epidemic. The study was featured in the paper, ‘An ecological study of obesity-related cancer incidence trends in Australia from 1983 to 2017’, published in The Lancet Regional Health - Western Pacific.
The Daffodil Center analysed 35-year rates of ten cancer types in Australia, which according to World Health Organization and World Cancer Research Fund findings, are associated with obesity. The cancers analysed were those of the bowel, liver, gallbladder, pancreas, breast (postmenopausal women), uterus, ovary, kidney and thyroid, and multiple myeloma.
For their study, the researchers examined Australian incidence data for ten obesity-related cancers among people aged 25–84 years, diagnosed from 1983 to 2017, obtained from the Australian Cancer Database. They used age–period–cohort modelling and joinpoint analysis to assess trends, estimating incidence rate ratios (IRR) by birth-cohort for each individual cancer and pooled, and the annual percentage change. The analyses were also conducted for non-obesity-related cancers over the same period.
The total number of cancers where some proportion is obesity-related, diagnosed from 1983-2017, was 1,005,933. This grouping was 34.7% of cancers diagnosed. They reported that IRR of obesity-related cancers increased from 0.77 (95% CI 0.73, 0.81) for the 1903 birth-cohort to 2.95 (95% CI 2.58, 3.38) for the recent 1988 cohort relative to the 1943 cohort (Figure 1). The IRRs of non-obesity related cancers were stable with non-significant decreases in younger cohorts. These trends were broadly similar across sex and age groups.
Senior Research Fellow and lead author of the research, Dr Eleonora Feletto, said the study found for cancers with an association to overweight and obesity, incidence was almost three times higher in young people, compared to those born in the late 1940s: "For cancers without a clear association to overweight and obesity, we didn't see the same rise, highlighting the growing concern for obesity as a public health epidemic."
Compared with other cancers, those strongly associated with obesity increased in incidence between 1983 and 2017 at an alarming rate.
Chair of Cancer Council's Nutrition, Alcohol and Physical Activity Committee, Clare Hughes, said Australia is facing a large public health issue. "We are a wealthy country that's proud of its health system, yet we've seen obesity rates continue to increase over decades."
The research also showed a sharp increase in obesity-related cancers for people born after 1960, a time where rates of obesity in Australia began to rise significantly.
"Recent decades have seen changes in food supply, eating patterns, a rise in convenience and ultra-processed foods, overconsumption and inactive lifestyles - all of which create an environment that leads to increased body mass and poor health. With our research showing that the results of the obesity epidemic are leading to escalating preventable cancer incidence, governments need to take strong action to support improved nutrition and physical activity," explained Hughes.
Common cancers with an association with obesity, such as bowel cancer, saw up to three-fold increases in incidence for younger people, while less common cancers associated with obesity, such as liver, kidney, uterine, thyroid and pancreatic cancers, saw similar, if not higher, increases in incidence.
"In total, more than one million cases of cancer types that have an established association with obesity were diagnosed over the 35-year period," added Feletto. "The extent to which obesity directly causes these cancers varies. A pattern has emerged across all ten, showing that cancers related to obesity are increasing in incidence at a faster rate than those that are not obesity related."
Halting and reversing the rise in obesity rates by 2030 is a target of both the National Preventive Health Strategy and the National Obesity Strategy. Cancer Council is calling on all governments to implement the recommendations of the National Obesity Strategy to raise awareness of the health consequences of obesity and introduce policies to address the environmental factors that contribute to excess weight gain.
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