Obesity-related cancers increasing in young US adults

An observational study using data covering more than half of the US population suggests that incidence rates of cancers linked to obesity are increasing most rapidly in young adults. The findings, published in The Lancet Public Health on World Cancer Day (4 February), could indicate that an even greater disease burden is on the horizon.

Most epidemiological studies have focused on older populations, so the effect on cancer risk of excess body weight in early life, or of weight gain in young adulthood, is not well understood. In some cancers, excess body weight during early adulthood could be a more important influence on cancer risk than weight gain in later life. This is the first study to examine contemporary incidence trends in young adults for a comprehensive list of cancers in the United States.

The study authors analysed incidence data from 25 state cancer registries, covering 67% of the US population. They considered 30 of the most common cancer types, including 12 obesity-related cancers in people aged 25 to 84 years, diagnosed between 1995 and 2014. During this time frame, there were 14,672,409 cases of the 30 types of cancer.

Incidence of half of the obesity-related cancers — specifically, multiple myeloma and cancers of the colorectum, uterine corpus, gallbladder, kidney, pancreas and thyroid — was found to have increased in younger adults (25 to 49 years). Incidences also rose in older adults, except for colorectal cancer, but by a smaller percentage. In all seven of these cancer types except for thyroid cancer, the younger the age group, the greater the size of the increase.

For example, in pancreatic cancer the average annual change was equal or less than 1% in people aged 40–84, 1.3% in those aged 35–39 and 2.5% in those aged 30–34. In the youngest age group (25–29), it was 4.3%. Across the six cancer types, the annual increase ranged from 0.4% in uterine corpus cancer to 3% in kidney cancer among those aged 45–49, and from 1.4% for multiple myeloma up to 6.2% in kidney cancer in those aged 25–29.

While the rates are increasing more quickly in younger adults, it is important to note that overall incidence is lower than in older adults where the majority of cancers are diagnosed. For example, around two pancreatic cancer cases were diagnosed in every 100,000 25- to 49-year-old per year from 2010–2014, compared with around 37 in every 100,000 50- to 84-year-old. But that’s not necessarily a comfort, as the study could serve as a warning of things to come.

“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 study co-author Dr Ahmedin Jemal, from the American Cancer Society. “Most cancers occur in older adults, which means that as the young people in our study age, the burden of obesity-related cancer cases and deaths is likely to increase even more.”

Overall, the findings could reflect the obesity epidemic of the past 40 years, with obesity rates having more than doubled in the US between 1984 and 2014. Worryingly, obesity is now one of the most preventable causes of cancer in both the US and the UK — around 1 in 12 cases in the US are caused by excess weight and more than 1 in 20 in the UK.

“Over the past few decades, death rates have been in decline for most cancers, but in the future obesity could reverse that progress, barring any interventions,” said study co-author Dr Ahmedin Jemal. “Younger generations are experiencing earlier and longer-lasting exposure to excess fat and to obesity-related health conditions that can increase cancer risk.”

Lead author Dr Hyuna Sung, also from the American Cancer Society, added: “Obesity is associated with health conditions that can contribute to the risk of cancer. For example, diabetes, gallstones, inflammatory bowel disease and poor diet can all increase the burden of cancer. The quality of the American diet also has worsened in recent decades. More than half of adults who were 20 to 49 years old between 2010 to 2012 reported poor dietary habits, such as eating little fruits, vegetables, whole grains, fish and shellfish at the same time as eating too much salt, fast food and sugary drinks.”

The authors suggest that restrictions on advertising calorie-dense food and drinks, taxes on sugary drinks and urban planning that promotes physical activity could be effective strategies to stem the emerging trend. They have also called for increased obesity screening.

Image credit: ©stock.adobe.com/au/Andrey Popov

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