In August, the American Cancer Society published shock findings of a major study: millennials and the tail-end of Generation X were at more risk of developing 17 types of cancer than older generations.

Overall, those born in the 1980s and 1990s are increasingly likely to develop cancer in their 30s and 40s compared to Baby Boomers and earlier generations.

For example, people born in 1990 were between two and three times more likely to develop cancers of the small intestine, thyroid, kidney and pancreas than those born in 1955.

The study also found that 9 of the 17 cancers that were increasing in young people had been declining in recent years in older generations.

These cancers were:

• Breast cancer that is estrogen receptor-positive
• Uterine cancer, also called endometrial cancer
• Colorectal cancer
• Stomach cancer
• Gallbladder cancer
• Ovarian cancer
• Testicular cancer
• Anal cancer (in men)
• Kaposi sarcoma (in men)

This new study looked at data from almost 24 million cancer patients collected from US cancer registries over a 20-year period, beginning in 2000. They also found that people born more recently are getting cancer at a younger age.

A 2023 study reported that the early-onset incidence of 29 cancers increased by about 79 per cent globally between 1990 and 2019.

Early-onset cancer deaths have risen by about 28 per cent during that time.

Since 2019, there have been predictions that millennials face a “triple threat of being sicker, broker, and dying younger than the previous generation”. 

At least they’re keeping their chins up, right?

Last year, the University of Sydney research found deteriorating mental health was particularly pronounced among people born in the 1990s.

The authors alternatively found little evidence that mental health was worsening for those born prior to the 1980s.

Why more cancer in younger people?

The best scientists can do so far is name “probable culprits“.

Some theories amount to millennials being canaries in coal mine – both victims and signallers of a poisoned world.

According to the Memorial Sloan Kettering Cancer Center, researchers are exploring exposures to medications and other substances during fetal development and early childhood.

Lounging around is nice, but too much of it hurts the heart. Photo: Getty

Environmental factors, such as exposure to pollutants and chemicals, and changes in the gut microbiome are also being investigated.

Lifestyle and behaviour changes get most of the blame. While millennials went through childhood, type 2 diabetes, obesity and a diet polluted with convenient and cheap ultra-processed sugars all came into excessive vogue.

Plus, from morning to night, millennials were the first generation to carry the digital world in their pockets.

This contributed to a dangerous rise in sedentary behavior – which has emerged as one of those probable cancer-causing culprits. 

A 2019 study found that:

“Independent of exercise and obesity, prolonged sedentary TV viewing time, a surrogate for a more inactive lifestyle, was associated with increased risk of young-onset CRC (colorectal cancer), particularly of the rectum.”

New study     

According to new research from Colorado University Boulder and University of California Riverside, “millennials now spend more than 60 hours per week sitting”.

That’s on average. Some participants in the study were sitting 16 hours a day or 94 hours a week – which is getting up their with the habits of doddery grandparents.

The researchers didn’t look at the relationship of prolonged sitting with cancer risk, focusing instead on heart disease risk and other signs of accelerated ageing.

The study involved more than 1000 former or present-day Colorado residents, including 730 twins. The participants ranged in age from 28 to 49, average age 33.

The researchers looked at two key measures of heart and metabolic aging: total cholesterol/high-density lipoprotein and body mass index (BMI).

The study found that, “essentially, the more one sat, the older one looked”.

It found that meeting the minimum recommended physical activity guidelines – a touch more than 20 minutes per day of moderate exercise – “isn’t enough to counter the hazards of spending most waking hours in a seat”.

Instead, “young adults who sat 8.5 hours per day and performed at or below current exercise recommendations could enter a ‘moderate to high risk’ category for cardiovascular and metabolic disease”.

Vigorous exercise did buffer these impact, but also reducing sitting time may be necessary to avoid accelerated ageing.

Senior author Chandra Reynolds is a professor in the Department of Psychology and Neuroscience and the Institute for Behavioral Genetics. She said:

“Our research suggests that sitting less throughout the day, getting more vigorous exercise, or a combination of both may be necessary to reduce the risk of premature aging in early adulthood.”

First author Ryan Bruellman is a doctoral candidate in the Department of Genetics, Genomics and Bioinformatics at UC Riverside.

Bruellman said that after the COVID-19 pandemic, he noticed that he and other people his age were sitting more. He set out to learn more about the consequences.

“Young adults tend to think they are impervious to the impacts of aging. They figure, ‘My metabolism is great, I don’t have to worry until I’m in my 50s or 60s,’” said Bruellman.

“But what you do during this critical time of life matters.”