Why do so many young people suddenly have cancer?

A Vox reader asks: What happened between Gen X and millennials to send cancer rates soaring?

That’s the million-dollar question in medical science today.

You’ve surely seen the headlines, but let’s recap the most pertinent data: One in five new colorectal cancer patients in the United States is under 55, according to a Wall Street Journal analysis of data from the National Cancer Institute. That is nearly twice the rate in 1995. A recent meta-analysis led by the American Cancer Society found that 17 of the 34 most common cancers — including those of the small intestine, pancreas, and kidney — are occurring more frequently in younger people. Some of them had previously been declining but are now on the upswing again.

Here’s the really scary part: While death rates for colorectal cancer patients over 65 are dropping, they are increasing among younger patients. Scientists say these early cancers can be more deadly because they are often not caught until it’s too late for treatment. (Colonoscopies are not recommended until age 45.) 

As a millennial prone to health anxiety, I have the same question: Why is this happening to my generation? Unfortunately, the short answer is: We do not know for certain. But let’s dig into the long answer.

What do we actually know about cancer risk factors?

We’ve long known that weight and exercise help determine a person’s risk of developing a range of cancers. The increase in global obesity rates since the mid-1990s has likely played a significant role in the rise in early-onset cancers, especially those in the gastrointestinal tract. 

But over the past decade, new research has shown that other factors — specific foods in the diet, other behaviors such as sleep, environmental pollutants — may also contribute to cancer risk. These risk factors are not as well understood as obesity or lack of exercise, but scientists are now racing to catch up.

Scientists have found that certain diets, including those rich in so-called ultra-processed foods, are associated with a higher risk of GI cancers, regardless of a person’s BMI. Higher alcohol consumption is likewise correlated with a higher risk of developing colorectal cancer early. Exposures to toxins in the environment and in everyday goods, including chemicals found in makeup and hair products and formaldehyde in building materials, are now also suspected to increase risk for a wide range of cancers in younger patients, particularly if the exposure occurred at pivotal points in a person’s life. Getting less sleep or interrupted sleep may also be a factor in developing breast, colon, ovarian, and prostate cancers. 

“Sleep and circadian rhythm is an important component of health,” Andrew Chan, who is leading an international research project on early-onset cancer, told me. People today “are probably getting less sleep or having more disrupted sleep for a variety of reasons. Is that potentially changing our biology in a way that is detrimental?”

Cancer researchers are also obsessed with the microbiome, the ecosystem of bacteria that is concentrated in a person’s gut. Certain kinds of microbiome bacteria are associated with the development of GI cancers, but researchers are still puzzling out whether those changes are a cause or a consequence of the disease. 

This is truly a global challenge. The increases in early cancer cases and deaths are most pronounced in wealthy countries, but developing nations are contending with some of the same environmental contaminants, particularly microplastics, and they are already seeing increasing death rates from other obesity-related diseases. As poorer countries become more economically developed, they also expect to see more “first world” health problems — including cancer. 

“This is going to be a problem that is going to be facing us as our economy gets stronger,” Bhawna Sirohi, medical oncology director at the Balco Medical Center in Raipur, India, told me earlier this year. It’s “facing us, the West, everywhere.”

Why do different generations have different cancer risks?

Since I started reporting on this slow-rolling crisis at the beginning of the year, easily the most interesting thing I have learned is that your risk of many types of cancer likely depends in part on something that was completely out of your control: when you were born. 

If you go back to the American Cancer Society’s meta-analysis, people born in 1975 experience nearly twice the rate of small-intestinal cancers as people born in 1955. For people born in 1990, those cancer rates have grown to nearly four times what they were for people born in the middle of the 20th century. You can see the same general trajectory for kidney, liver, pancreas, and bone marrow cancers.

These generational differences would support the increasingly accepted idea that recent environmental changes and widespread alterations to our diets may be contributing to the rise in early-onset cancers. A 2020 study in the journal Gastroenterology noted that a person’s GI cancer risk had previously been measured by their family history, yet three in four new cancer patients have no such history. The researchers concluded that the surge could instead “result from generational differences in diet, environmental exposures, and lifestyle factors.”

Systematic reviews of the available research, including one published in Frontiers in Nutrition in 2022, have identified consumption of a lot of deep-fried foods, processed foods, foods high in fat, and sugary drinks and desserts, as well as low folate and fiber consumption, as risk factors. People have been eating more and more of those products over the years — well, except for fiber, which is very good for human digestion and yet horribly underconsumed in the US. My generation drinks too much alcohol too, even while the evidence of its carcinogenic properties continues to pile up.

Scientists hypothesize that changes in our environment, such as the proliferation of microplastics and forever chemicals that are linked to certain cancers and may allow others to metastasize more easily, could be another contributing factor. From food containers to synthetic clothing, we are exposed to and ingest these tiny particles every day. 

According to a paper published last year by a New Zealand research team, the upticks in cancers among young adults matched the timeline that we would expect from the multiplication of microplastics in the environment. Research on cellular and rodent models has suggested that microplastics could promote tumor growth. Though more research is needed, we already know these materials contain chemicals that can disrupt hormones and pose a risk to our health.

In the same vein, scientists increasingly suspect that exposures to risk factors at certain ages — whether in utero, early childhood, or early adulthood — could be playing an important role in a person’s risk of developing cancer at a young age. Preliminary findings, such as a study that found consuming more sugary drinks in adolescence was associated with a higher risk of developing colorectal cancer early in women, lend support to those theories.

Researchers are working to sharpen our understanding of these causes and of how to treat and prevent these devastating diseases. We still have a lot to learn about these new variables in our cancer risk. While it’s easy to feel powerless in the face of that uncertainty, all of the long-understood recommendations still apply and can make a world of difference in our health and disease risk: We can try to eat right, drink less alcohol, and be more active.