As the world marks world cancer day, a sharp increase in the rate of obesity-linked cancers among young adults in the United States could foreshadow a reversal in the overall decline in cancer mortality, researchers warned 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, a medical journal.
During the period examined, the incidence of pancreatic cancer, for example, increased by about one percent per year for adults aged 45 to 49. Among 30 to 34-year-olds, the average annual percent increase was more than twice that high.
And among 25 to 29-year-olds, the rate jumped by 4.4 percent 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 percent), gallbladder (3.71 percent), uterine (3.35 percent), and colon (2.41 percent).
“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, USA.
Obesity has more than doubled in the United States over the last four decades.
It has also risen sharply in other rich nations and, more recently, the developing world. Today, some 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 to 37 cases for every 100,000 people aged 50 to 84.
Overall, the number of people in the United States who succumb to cancer has declined.
From 1980 to 2014 — when cancer claimed some 20 million lives — mortality dropped by 20 percent, 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 1 in 12 cases in the US are caused by excess weight, and more than 1 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 percent of the population.
The data covered 30 types of cancer, 12 of which had previously been linked to obesity.