Poor sleep may be fuelling the global rise in under-50s being diagnosed with cancer, two large studies presented at the world’s largest cancer conference suggest. Researchers from MD Anderson Cancer Center in Houston, Texas, analysed health data for more than 18 million US adults aged between 18 and 50 and found that people with irregular sleeping patterns were more likely to develop early-onset bowel, breast, uterine or ovarian cancer. In some cases, under-50s diagnosed with insomnia were three times more likely to develop cancer within five years.
The findings come against a stark backdrop: worldwide cases of early-onset cancer increased from 1.82 million in 1990 to 3.26 million in 2019 — a rise of almost 80% over three decades. Cancer deaths among people in their 40s, 30s or younger rose by 27%. In the UK, cancer incidence rates among people aged 25 to 49 increased by approximately 22% between 1993–95 and 2016–18. Between 2001 and 2019, incidences of 16 out of 22 cancers in younger women and 11 out of 21 cancers in younger men in England increased significantly. Around 31,000 cancers were diagnosed in people aged 20 to 49 in England in 2023 alone.
How poor sleep could increase cancer risk
Experts point to several biological pathways that may explain the link between sleep disruption and early-onset cancer. Adequate sleep is crucial for a robust immune system, which plays a role in identifying and eliminating abnormal cells, including potentially cancerous ones. Just one night of poor sleep can significantly reduce the activity of natural killer cells, a type of white blood cell vital for fighting disease. Chronic sleep deprivation may weaken immune surveillance, allowing cancer cells to evade detection and proliferate.
Lack of sleep is also associated with increased levels of inflammation in the body. Chronic inflammation can create an environment conducive to tumour growth and metastasis. Elevated levels of pro-inflammatory cytokines such as IL-6 and TNF-α — linked to sleep disorders — can impair immune surveillance and promote tumour growth. Disruptions to the body’s internal clock, or circadian rhythms, can affect critical cellular processes like cell division and DNA repair. Melatonin, a hormone produced during sleep that has antioxidant and anti-inflammatory properties, may be reduced with insufficient sleep or exposure to light at night, potentially contributing to cancer development.
Dr David Garley, a GP and director of the Better Sleep Clinic in Bristol, England, said the impact of insomnia on someone’s risk of other health conditions, including cancer, was of “growing interest”. He cautioned that the studies had identified an association rather than proof that sleep disruption caused cancer in under-50s. “If you’re sleeping badly, we know that one of the roles of sleep is restoring the immune system,” he said. “So if your immune system takes a bit of a hit, then I suppose it would make sense that your risk of some cancers may increase. But it also might be the other way around. It could be that if you have cancer, and it’s not yet clinically obvious, it could be causing some change in how you sleep.”
Garley also noted that poor sleep can lead to lifestyle changes that themselves increase cancer risk. “When sleep-deprived it’s difficult to live a healthy life — there is more drinking, more obesity, less exercise, more smoking etc — and these may be what causes any possible increased risk.”
Claire Coughlan, the clinical lead at Bowel Cancer UK, said bowel cancer was still more common in over-50s, but there was a growing body of evidence globally that cases were increasing in younger people. “We don’t know exactly why this is yet, but researchers currently believe it may be due to genetics and lifestyle factors,” she said. “This study’s conclusion that insomnia may be a potential risk factor in early-onset colorectal cancer could go some way to helping us understand the reasons behind this increase. The findings of this study are worth exploring further.” Bowel Cancer UK’s “Never Too Young” campaign highlights that one in 20 bowel cancer cases in the UK occur in those under 50, and rates in this age group have increased. Younger patients are more likely to be diagnosed at a later stage and after multiple GP visits. In England, rates of early-onset bowel cancer increased by 22% between the early 1990s and 2018.
Megan Winter, a health information manager at Cancer Research UK, said: “These studies explore whether there could be a link between insomnia and some types of cancer in people under 50, but more research is needed, particularly looking at people over longer periods of time, before we can draw any conclusions.” In the meantime, she added, people could reduce their risk of cancer by not smoking, maintaining a healthy weight and staying safe in the sun.
Identifying the causes of rising cancer rates among younger adults has become a global health priority. More than one million under-50s die from cancer each year, according to research published in BMJ Oncology. While obesity has been identified as a major driver — a study in England found rising average BMI scores outweighed other risk factors like smoking and alcohol — it is not sufficient to explain the overall rise, pointing to “additional, suspected, or currently unknown causes”. Other factors under investigation include environmental exposures such as microplastics and polyfluoroalkyl substances, changes in diet, and the totality of environmental exposures known as the “exposome”. The researchers from MD Anderson described sleep disruption as a “clinically relevant, potentially modifiable risk factor in early-onset cancer risk stratification” that “warrants further investigation”.
