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Steep rise in obesity increasing cancer risk in younger generations

Cancers linked to obesity are rising at a faster rate in millennials than in older generations in the US, BBC News reports the American Cancer Society has said. It said a steep rise in obesity in the past 40 years may have increased cancer risk in younger generations. And it warned the problem could set back recent progress on cancer. The society studied millions of health records from 1995 to 2014.

In the last few decades, there has been mounting evidence that certain cancers can be linked to obesity. Researchers found that the rates of six out of 12 obesity-related cancers (colorectal, uterine, gallbladder, kidney, pancreatic and multiple myeloma – a blood cancer) all went up, particularly in people under the age of 50. And, the report says, they found steeper rises in successively younger generations aged 25 to 49 – and particularly in millennials, in their 20s and 30s.

For example, the risk of colorectal, uterine and gallbladder cancers has doubled for millennials compared to baby boomers, now aged 50 to 70, at the same age.

Some of these cancers increased in people over 50 too, but the rises were not as steep. Researchers say this trend may be down to the rapid rise in obesity in the last few decades with "younger generations worldwide experiencing an earlier and longer exposure to the dangers of extra weight".

Dr Ahmedin Jemal, from the American Cancer Society, said in the report: "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. 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 are likely to increase even more." But the researchers could not explain why the rates of only half of the 12 obesity-related cancers had increased.

Meanwhile, they found cancers linked to smoking and infections were declining in younger age groups.

Dr Brenda Birmann, from Brigham and Women's Hospital in Boston, said that it was possible that risk factors other than obesity could play a part and this warranted further investigation. "Importantly, the findings suggest the need for further close epidemiological monitoring of cancer incidence trends in younger adults," she said in the report.

According to the charity Cancer Research UK, obesity is the second biggest preventable cause of cancer in the UK, after smoking. The report says research suggests bowel cancer, womb cancer, oesophageal (food pipe) cancer, cancer of the kidney, liver, upper stomach, gallbladder, ovarian, thyroid, meningioma (a type of brain tumour) and multiple myeloma (a type of blood cancer) and breast cancer in women after the menopause have all been linked to obesity.

Researchers say the risk increases as people get more overweight.

But of course, obesity is only one factor – the environment, genetics and other issues can also come into play. The report says not everyone who gets these cancers will be overweight and everyone who is obese will not necessarily get these cancers. And scientists are clear that losing even small amounts of weight can help reduce the risk of cancer.

Background: Cancer trends in young adults, often under 50 years, reflect recent changes in carcinogenic exposures, which could foreshadow the future overall disease burden. Previous studies reported an increase in early onset colorectal cancer, which could partly reflect the obesity epidemic. We examined age-specific contemporary incidence trends in the USA for 30 common cancers, including 12 obesity-related cancers.
Methods: We obtained incidence data for invasive cancers among people aged 25–84 years diagnosed from Jan 1, 1995, to Dec 31, 2014, for 25 population-based state registries in the USA. All patients in the registry were included in the analyses. We considered the 20 most common cancer types and 12 obesity-related cancers (30 cancer types in total). We used age-period-cohort modelling to estimate average annual percentage change in incidence rates by 5-year age group (25–29 years to 80–84 years in 5-year increments) and incidence rate ratios (IRR) by birth cohort (10-year overlapping birth cohorts from 1910–19 to 1980–89 in 5-year increments). No exclusion criteria were applied after including all invasive cancer cases based on age group and diagnosis year.
Findings: From 1995 to 2014 there were 14 672 409 incident cases for 30 types of cancer. Incidence significantly increased for six of 12 obesity-related cancers (multiple myeloma, colorectal, uterine corpus, gallbladder, kidney, and pancreatic cancer) in young adults (25–49 years) with steeper rises in successively younger generations. Annual increases ranged from 1·44% (95% CI −0·60 to 3·53) for multiple myeloma to 6·23% (5·32–7·14) for kidney cancer at age 25–29 years, and ranged from 0·37% (0·03–0·72) for uterine corpus cancer to 2·95% (2·74–3·16) for kidney cancer at age 45–49 years. Compared with people born around 1950, IRRs for those born around 1985 ranged from 1·59 (95% CI 1·14–2·21) for multiple myeloma to 4·91 (4·27–5·65) for kidney cancer. Conversely, incidence in young adults increased in successively younger generations for only two cancers (gastric non-cardia cancer and leukaemia), and decreased for eight of the 18 additional cancers, including smoking and HIV infection-associated cancers.
Interpretation: The risk of developing an obesity-related cancer seems to be increasing in a stepwise manner in successively younger birth cohorts in the USA. Further studies are needed to elucidate exposures responsible for these emerging trends, including excess bodyweight and other risk factors.

Hyuna Sung, Rebecca L Siegel, Philip S Rosenberg, Ahmedin Jemal

[link url=""]BBC News report[/link]
[link url=""]The Lancet Public Health abstract[/link]

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