PARIS: 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.
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 commented, 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 (IARC) 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, less than half of primary care physicians in the US regularly measure the body-mass index (BMI) 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 for too little fruits, vegetables and whole grains, and too much salt, fast food and sugary drinks, she said.