3x as many cancers linked with physical inactivity than previously thought
New research suggests that more than three times as many cancer cases are attributable to physical inactivity than previously thought.
Associate Professor Brigid Lynch, senior author of the paper, saw evolving evidence that physical inactivity was associated with at least 13 types of cancer – not just three types, as researchers once believed – and wanted to update the estimates based on Australian activity levels and cancer rates.
Since Australia started a database tracking cancer diagnoses 40 years ago, the line on the chart has steadily crept up. In 1982, there were less than 50,000 cases a year compared with more than 150,000 in 2021.
Since then, an increase in knowledge suggests that between 30 and 50 per cent of cases are preventable and result from modifiable factors like smoking, poor diet, alcohol consumption, infection, being overweight and physical inactivity.
For the new study, funded by the Victorian government and published in the Journal of Science and Medicine in Sport, researchers looked at the physical activity data of Australians, then the incidence of those 13 cancer types a decade later. Researchers then conducted analyses to control for confounders and to determine how much activity would have been preventative.
They estimated that 6361 – or nearly 5 per cent – of cancers diagnosed in 2015 were attributable to physical inactivity.
This is 350 per cent more than previous estimates and relates to breast, colon, bladder, endometrial, kidney, oesophageal adenocarcinoma, gastric, non-Hodgkin lymphoma, head and neck, myeloma, myeloid leukaemia, liver and gallbladder cancers.
Thousands of diagnoses could have been prevented with a modest increase in movement of just 30 to 40 minutes a week, says Lynch. “But the more you can do the better and, for prevention, Cancer Council recommends people try to aim for about 300 minutes a week or about an hour, five days a week ... which can be accumulated by just doing small amounts throughout the day.”
Experts are still trying to understand the mechanism, but they know sex hormones, for instance, play an important role in endometrial as well as breast cancer (which is increasing among men and women).
“Physical activity reduces the amount of circulating oestrogens and that is very strongly linked to oestrogen receptor positive breast cancer, which is a common type,” explains Lynch, who works with Cancer Council.
Physical activity also improves body composition, which matters given adipose tissue increases oestrogen levels.
They also know that people with metabolic conditions, including poor insulin signalling or type 2 diabetes, are more likely to get colorectal cancer and that physical activity increases insulin sensitivity.
Then there is inflammation, which plays a role in the development of many cancers.
“Our skeletal muscle produces anti-inflammatory peptides, and they are excreted during periods of exercise,” Lynch says. “That could be a pathway by which having more skeletal muscle, which comes from exercise, helps reduce your inflammation.”
While any type of activity reduces risk, the significance of muscle mass in a cancer suppressing environment may make regular resistance training particularly powerful, says Professor Rob Newton, the deputy director of Edith Cowan University’s Exercise Medicine Research Institute.
He adds that physical activity has a “huge influence” over the functionality of the immune system. “When you have a more effective, more surveillant system that can identify and destroy those precancerous cells, they never progress to a malignancy.”
Despite this, there has been little emphasis on physical activity in cancer prevention. “This is something we really need to address... we can’t keep throwing drugs at these things,” says Newtown.
Though the data is “staggering”, the findings are not surprising, says Ainslie Sartori, the deputy chair of Cancer Council’s Nutrition, Alcohol and Physical Activity Committee. “These findings will prove to be vital in cancer prevention policies that promote physical activity among Australians.”
Currently, there is no national physical activity plan to inform governments about creating systems that promote being active, like less car-centric cities, improved bike paths, more public transport and access to green spaces.
To address this, Sartori and Lynch are urging the government to implement the National Preventive Health Strategy which recommends a physical activity policy, as well as urban design, education, and support to encourage and enable people to move more.
It is essential, Sartori says. “To promote better environments for physical activity, to support Australians in building better habits [will] help reduce their risk of cancer later in life and ultimately save lives.”
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