Fat youngsters are ruining all the good work done to cut cancer rates
Cancer deaths are dropping in the US, but obesity threatens to reverse that trend, say experts
A sharp increase in the rate of obesity-linked cancers among young adults in the US could foreshadow a reversal in the overall decline in cancer mortality, researchers warned on Monday.
In a sweeping study covering two-thirds of the US population, they showed that half a dozen cancers for which obesity is a known risk factor became more frequent from 1995 to 2015 among women and men under 50.
The younger the age bracket, the more quickly these cancers gained ground, they reported in The Lancet medical journal.
During the period examined, the incidence of pancreatic cancer, for example, increased by about 1% per year for adults aged 45 to 49. Among 30- to 34-year-olds, the average annual percent increase was more than twice that.
And among 25- to 29-year-olds, the rate jumped by 4.4% per year.
Comparing five-year age brackets from 25 to 80, the annual hike was similarly highest among the 25 to 29 cohort for four other obesity-linked cancers: kidney (6.23%), gallbladder (3.71%), uterine (3.35%) and colon (2.41%).
“Our findings expose a recent change that could serve as a warning of an increased burden of obesity-related cancers to come in older adults,” said co-author Ahmedin Jemal of the American Cancer Society.
Obesity has more than doubled in the US over the past four decades.
Mortality could rise
It has also risen sharply in other rich nations and, more recently, the developing world. Today, about two billion people are overweight or obese.
With few exceptions, cancer has been seen as a disease of ageing.
Indeed, the researchers note that the number of new cancer cases reported remains much higher in older age brackets, even if the rate of increase is now highest among young adults.
Two pancreatic cancer cases, for example, were diagnosed among every 100,000 24- to 49-year-olds from 2010 to 2014, compared with 37 cases for every 100,000 people aged 50 to 84.
Overall, the number of people in the US who succumb to cancer has declined.
From 1980 to 2014 – when cancer claimed about 20 million lives – mortality dropped by 20%, from 240 to 192 deaths per 100,000 people, due in part to reduced tobacco use.
“But in the future, obesity could reverse that progress,” Jemal cautioned.
“Obesity is now one of the most preventable causes of cancer in the US and UK – around one in 12 cases in the US are caused by excess weight, and more than one in 20 in the UK.”
Building on earlier research suggesting a link between obesity and more frequent colon cancers in young adults, Jamel and colleagues analysed all cancer cases from 1995 to 2015 in 25 US states, home to 67% of the population.
The data covered 30 types of cancer, 12 of which had previously been linked to obesity.
Too much junk food
For five of the 12, the rate of increase for new cases was highest in the youngest age group, and for a sixth – a form of bone marrow cancer called multiple myeloma – the biggest jump was among adults in their early 30s.
Of the other 18 types of cancer, only two showed a similar trend, with the others either stable or, for those related to smoking and infection, in decline.
“The investigators speculate that these findings are driven in part by the obesity epidemic, a hypothesis that is both provocative and plausible,” Catherine Marinac from the Dana-Farber Cancer Institute and Harvard University’s Brenda Birmann said, also in The Lancet.
Still unexplained, however, is why the six other forms of cancer classified by the UN’s International Agency for Research on Cancer as related to obesity did not also show similar rates of increase among younger adults.
The authors called for more aggressive screening for obesity by front-line doctors, and called on them to warn patients about the cancer risk of being seriously overweight.
Currently, fewer than half of primary care physicians in the US regularly measure the body-mass index of their patients.
“The quality of the American diet has worsened in recent decades,” said lead author Hyuna Sung, also of the American Cancer Society.
More than half of 20- to 49-year-olds eat far too few fruits, vegetables and whole grains, and too much salt, fast food and sugary drinks, she said.