Irregular Sleep May Lead to Cancer Risk, Even Heart Disease

VIVA – Based on a seven-year study of middle-aged and older adults, people who have irregular sleep may lead to cancer risk and even heart disease, compared with people who have regular sleep schedules. 

"To my knowledge, our study is the largest to look at how sleep irregularity affects all-cause mortality," or death from any cause, Matthew Pase, an associate professor of psychology at Monash University in Australia and a co-author of the study. 

Sleep regularity may impact mortality independently of sleep duration, he added. 

Pase and his colleagues recruited nearly 90,000 people living in the UK to wear movement-tracking devices on their wrists for around a week; the participants ranged from about 40 to 70 years old. 

By using a statistical model to estimate when people were asleep or awake from the recorded movement data, the researchers calculated a sleep regularity score for each participant, defined as the probability that a person was awake or asleep at the same time between any two consecutive days. 

One group of participants was scored as having "low sleep regularity," as they had a 41% chance of being asleep or awake at the same time for two days in a row; this put the group in the fifth percentile of sleep scores, overall. Those with "average" sleep regularity, who were in the 50th percentile, had a 61% chance of being asleep at the same time on consecutive days.

Within about seven years of the team collecting this data, 3,010 of the participants died. Those with low sleep regularity scores were 46% more likely to die of any cause within the follow-up period, compared with people with average scores. 

Of the people who died, 1,701 died of cancer, and 616 died of cardiovascular disease. People with low sleep regularity scores were 33% more likely to die of cancer, and 73% more likely to die of cardiovascular disease, than people with average scores. 

A third group of people with "high" sleep regularity scores had a slightly lower-than-average chance of death, overall, and from cancer and heart disease, specifically, but their risk wasn't significantly different than the "average" group.

The analysis took into account differences in participants' age, ethnicity, sex, smoking status, diabetes, existing heart conditions and cancer, education level, income, and how long they slept each night, on average.

Shifts in sleep and wake times can disrupt bodily processes, such as the repair of tissues and metabolism, so this may then increase chronic disease risk. 

However, it's also possible that bodily changes that contribute to the development of cancer and cardiovascular disease may have led to the observed differences in sleep regularity.