Working outside a typical 9-to-5 schedule can lead to long-term health risks such as poor sleep and increased exhaustion, according to research.

A study by New York University professor Wen-Jui Han examined the physical and mental effects of a “volatile” work schedule by examining data collected over 30 years from more than 7,300 people. The study observed that individuals with later work hours may have lower sleep quality, leading to poor health and depressive symptoms.

The data comes from the National Longitudinal Survey of Youth-1979 (NLSY79), a project that follows the lives of American youths born between 1957 and 1964, and the study looked at individuals starting at the age of 22 and how their work schedules affected their health by age 50.

NLSY79 defined a “standard” work schedule as beginning as early as 6 a.m. and ending by 6 p.m. An “evening” schedule begins at 2 p.m. or later and ends by midnight. “Nights” are defined as 9 p.m. at the earliest and 8 a.m. at the latest, while the survey also included “variable” hours for split or irregular shifts and “not working” for participants without work.

Sleep deprivation that comes from non-standard work schedules disrupts circadian rhythm and can result in health issues that researchers have labeled as “Shift Work Sleep Disorder (SWSD).”

According to Han’s study, people who started working standard work schedules in their 20s but transitioned to variable hours in their 30s experienced significantly fewer hours of sleep per day compared to those with stable schedules. 

The stress that comes from unusual work schedules can lead to increased anxiety and depression and a high risk of hypertension, obesity and stroke. Results also showed that those with abnormal schedules are even more likely to have poorer health than those who aren’t working.

“This has repercussions,” Han said to the Daily Mail. “People with work patterns involving any degree of volatility and variability were more likely to have fewer hours of sleep per day, lower sleep quality, lower physical and mental functions, and a higher likelihood of reporting poor health and depressive symptoms at age 50 than those with stable work schedules.”

Furthermore, the study showed disparities in results depending on demographics and background. The study showed that women are more likely to experience sleep disorders than men, and a “higher share” of African Americans with non-standard work schedules has led to less sleep within that population.

As workplaces change and evolve over the years, and with certain jobs requiring different hours compared to “standard” office jobs, the study hopes to put into light the adverse effects that such schedules can have on long-term health for adults.

“This study’s findings highlight the dual challenges facing workers in vulnerable social positions who have jobs requiring nonstandard work schedules, both of which limit their access to resources that would allow them to achieve decent sleep health and physical and mental health outcomes,” the study concludes.