An Apollo Hospitals report released earlier this year sparked concerns for stating that India is the “cancer capital” of the world. Among others, the report showed an overall decline in Indians’ health and projected that 15.7 lakh Indians will have cancer by 2025. Breast, cervical, and ovarian cancers are the most frequently occuring in women, while lung, mouth and prostate cancers are the most frequent among men, the report continues.

This isn’t just the case in India: several reports have noted that cancers, particularly among younger people, seem to be on the rise worldwide. The WHO stated that global cancer rates will rise by more than 75% by 2050. One BMJ study said that early onset of 29 different types of cancers has risen 80% between 1990 and 2019 worldwide. Colorectal and other gastrointestinal tract cancers are the most common, with breast and lung cancers also comprising a significant proportion.

Statistics show that more than a dozen cancers are more prevalent among people under 50; and projections say that early-onset cancers will rise by 30% between 2019 and 2030. Importantly, despite many experts flagging factors like obesity and early screenings, these do not fully account for the rise in cases, according to Nature. In fact, clinicians told Nature that many patients who presented with cancer were seemingly fit and healthy, with few risk factors. “I have to say, most of our patients are not obese. Many are marathon runners. Many follow very healthy diets, eat organically. So we don’t know if it’s just diet and lifestyle factors or other things in our environment – pollutants, preservatives in our food,” noted Kimmie Ng, an associate professor of medicine at Harvard Medical School.

Why are early-onset cancers specifically concerning? Typically, cell damage begins after the age of 50, which is a risk factor for cancer. Cancers in people younger than that aren’t necessarily ruled out, but rising rates in a demographic that shouldn’t typically be susceptible to the disease indicates something deeper is going on – it is possible that early-onset cancers could be biologically different from typical cancers. “Some of the molecular characteristics and pathways of how something becomes cancerous are different between the older and younger groups… Younger adults tend to have a more aggressive-appearing cancer. They also tend to present at a more advanced stage that is not solely explained by a delay in diagnosis,” said Jeremy Kortmansky, MD, a Yale Medicine medical oncologist specializing in gastrointestinal cancers.

Other theories about risk factors besides obesity suggest the rise can be attributed to changes in the gut microbiota composition. “Emerging evidence suggests that the gut microbiome may influence host genetics, metabolism, and immunity during early-onset digestive system tumor development,” one study notes. This could explain the connection between cancer and diet: generations born in the 1960s were first exposed to modern lifestyles and environmental changes, which may have significantly changed the gut microbiome over time. Why does that matter? Because gut microbes play a key role in regulating our overall health, including immunity and digestion. Antibiotic usage – which has also risen – could also be a factor in people’s gut microbiomes changing, FT reported. Of 14 early-onset cancers, eight are digestive, “indicating the pathogenic importance of both the oral and intestinal microbiome,” a landmark study noted.

To get to the bottom of other contributing factors, a global team of researchers from the US, Europe and Asia are jointly studying the leading lifestyle and environmental factors leading to the uptick in early onset cancers, and will gather evidence from the US, Mexico, UK, France, Italy, and India. The global approach “...helps us to get insight into what’s common across these different parts of the world and what’s unique,” Andrew Chan, a cancer epidemiologist and clinical gastroenterologist at Harvard Medical School and Mass General Hospital who is co-leading the project, told Vox.

The international concern and incidence points to bigger factors than just individual lifestyles, as cancer has previously been associated with. A lot of cancer-prevention recommendations have thus far disproportionately focused on obesity, but the latest research has shown that deep-fried and processed foods, as well as foods low in folates and fiber are also factors regardless of body weight. Interrupted or reduced sleep, exposure to phthalates in makeup and hair products, and ultra processed foods are other potential risk factors.

The tidal wave of microplastics in our surroundings – infiltrating everything from our digestive tracts, reproductive tracts, and blood – is another emerging theory. One paper showed that rising rates of early-onset cancers coincided with the rise in microplastics in the environment. This age in human history, after all, is sometimes referred to as the Plasticene. Microplastics can cause DNA damage and oxidative damage, which are known risks for cancer. Shuji Ogino, a molecular pathological epidemiologist at Harvard Medical School, told Vox that people born in the early 20th century had a lower likelihood of developing cancer than people born in the later half, suggesting there is something systematically wrong with our environment and food production that is driving the trend. Ng calls this the “birth cohort effect” – the leading hypothesis is that unknown environmental exposures are predisposing individuals in their early lives.

Take the fact that India, China, and Japan have emerged as the top three Asian countries in terms of new cancer cases and deaths. The dominant cancers here aren’t digestive but tracheal, bronchus and lung cancers, according to a Lancet report, and cervical cancer is ranked second in cancers in women. “... smoking, alcohol consumption and ambient particulate matter (PM) pollution remained dominant among the 34 risk factors for cancer… The rising cancer burden due to increasing ambient air pollution is concerning in Asia," the researchers wrote. “In the low- and medium-income countries (LMICs) of Asia, oncologic infrastructure is either scarce or unaffordable, particularly in rural areas. Combined with a weak referral system, patients end up getting delayed diagnosis and treatment, leading to lower survival rates,” the researchers said.

Despite the rising rates, figures show that mortality – or the likelihood of death – from these cancers has declined. But owing to the growth in population, coupled with growing incidence of cancers and the lack of screening programs to detect them in younger cohorts, the total number of cancer deaths has increased. Dr Freddie Bray, the head of the International Agency for Research on Cancer (IARC) told The Guardian that cancer mortality will nearly double in lower-income countries: “Those who have the fewest resources to manage their cancer burdens will bear the brunt of the global cancer burden,” he said.

All this points to one big generational culprit: climate change driven by human activity. It impacts everything from “environmental exposures to ultraviolet radiation, air pollution, disruptions in the food and water supply, environmental toxicants, and infectious agents,” the Lancet noted. In general, a school of research says that the world’s injustices are making us sicker – environmental stressors and systemic injustice are factors in inflammation, which in turn leads to inflammatory diseases like cancer, according to Dr. Rupa Marya and Raj Patel, authors of Inflamed: Deep Medicine and the Anatomy of Injustice. It’s not just individual changes to lifestyle – early screening programmes, regulations on tobacco and food and beverage industries, and an overhaul of industrial consumption, are key to tackling the crisis.