It isn’t entirely clear why bowel cancer is on the rise among adults under 50
STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY
Rates of bowel cancer in younger adults have increased in countries around the world, though the trend appears to be most common in high-income nations.
Previous studies have shown that bowel, or colorectal, cancer rates have grown over the past few decades in this age group across several Western countries, including the US, Canada, Australia and the UK. This has led to speculation about whether Western lifestyles, such as diets high in meat or processed food, may be to blame.
To better understand the extent of the problem, Hyuna Sung at the American Cancer Society in Atlanta, Georgia, and her colleagues examined rates of bowel cancer in 50 countries and territories across the world. They generally collected data on its incidence from 1975 until 2017 using a World Health Organization database, although some countries didn’t start reporting this information until several years after 1975.
The team found that bowel cancer rates in people aged between 25 and 49 rose in 27 countries and territories. These include non-Western ones, such as Japan, and less wealthy nations, like Turkey, raising the possibility that Western lifestyles alone may not be behind the trend.
The increase is also unlikely to be related to improvements in screening, as most countries don’t routinely test people for bowel cancer until they are 50, the researchers wrote in their paper.
However, all 27 of the countries and territories have high or very high scores on the UN Human Development Index, which is based on average life expectancy, education level and income per person.
Additionally, all but six of them are considered high-income, according to the World Bank. Unlike most of the high-income nations studied, these six places saw bowel cancer cases increase among older adults at a pace equal to or greater than that of younger adults.
“I think there is still evidence in the trends that economic development and Westernisation of lifestyle does play a role,” says Andrew Chan at Harvard University, noting that many countries adopt aspects of this lifestyle as their economies grow. For instance, meat intake in Japan increased more than seven-fold between 1961 and 2021.
“That being said, I think there should still be consideration of the fact that there are probably other factors at play”, such as environmental pollutants, says Chan.
The researchers note that their study has several limitations, the most apparent being that countries in Africa and Asia and small islands were under-represented. Only one African nation – Uganda – was included, for example. Some countries also didn’t have complete datasets. For instance, figures for India were only representative of 4 per cent of the population there.
Still, these findings improve our understanding of how bowel cancer rates vary between many different countries, which could help us devise new ways to prevent the condition, says Chan.
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