The rate of obesity-related cancers in Australia has almost quadrupled in a few generations, new research suggests.
Researchers at the Daffodil Centre, a joint venture of Cancer Council New South Wales and the University of Sydney, analysed the rate of 10 obesity-linked cancers between 1983 and 2017.
They found that the incidence of these cancers was 2.95 times higher in the youngest age group – those born in the 1980s and early 90s – compared to those born in the 1940s, and nearly quadruple the rate for people born at the beginning of the 20th century.
Epidemiological studies have previously shown a link between the 10 conditions – colorectal, liver, gallbladder, pancreatic, uterine, ovarian, kidney, thyroid and postmenopausal breast cancers, as well as multiple myeloma – and obesity.
“While obesity is a cause of all those cancers, if there was not one single obese person in the population … cases of those cancers would still be diagnosed, but in significantly lower numbers,” said the study’s lead author, Dr Eleonora Feletto, a senior research fellow at the Daffodil Centre.
Metabolic, hormonal, and inflammatory alterations in cells increased the risk of cancer, and obesity was a contributing factor, Feletto said.
The figures came from the Australian Cancer Database, which documented 1,005,933 obesity-linked cancer diagnoses in Australians aged 25 to 84 over three and a half decades from 1983.
“The increase in obesity-related cancers has aligned with increases in obesity rates,” said the study co-author Clare Hughes, who chairs the Cancer Council Australia’s nutrition, alcohol and physical activity committee.
The researchers did not see the same significant increases in the rates of malignancies unrelated to obesity, which included lung, prostate, bladder and brain cancers.
Nearly two-thirds of the obesity-related cases diagnosed were breast cancer in postmenopausal women and colorectal – bowel – cancer.
“We are unable to claim that changing trends are solely a result of overweight and obesity,” the researchers wrote, emphasising that the observational study could not definitively infer cause and effect. “However, we know that overweight and obesity is an influential risk factor for these cancer types and, at least in part, is driving these changes.”
Feletto said: “The increase in incidence for cancers of the colorectum and breast in younger cohorts is something we’ve seen before, but this work shines light on this same trends for other cancers that we hear less about such as liver and pancreatic cancers.”
“The increasing incidence in younger cohorts here is really a call to action to support a better understanding of these tumours that also have poor outcomes.”
The exact drivers for the increasing rates of certain cancers in young people are unclear, experts have said. Other modifiable risk factors for cancer include alcohol intake, eating red and processed meat, smoking, and physical inactivity.
Australia has the sixth-highest proportion of overweight or obese people aged 15 and older in the OECD. Obesity rates have increased from 19% in 1995 to 31% in 2017–18, according to Australian Institute of Health and Welfare data.
Hughes noted body mass index (BMI) was more useful as a population measure to determine weight categories than for dictating an individual’s health status and risk. “Not every person who has excess weight or is obese is going to develop cancer,” she said.
The study’s findings highlighted an urgent need to stem further rises in preventable cancer rates, Hughes said. “It’s something that we can’t ignore and something that we must address.”
Hughes called on federal, state and territory governments to implement the recommendations of the national obesity strategy, which was released in March this year.
The research was published in the journal The Lancet Regional Health – Western Pacific.
