Black young adults may be more likely to lose sleep over student loan debt than people of other racial and ethnic groups, a U.S. study suggests.

Researchers surveyed former college students in their mid-20s to early 30s about their debt load and sleep habits. They found black people were more likely than white people to take out student loans - and they were also more likely to still have loans outstanding by the time they reached age 25.

Among those with student debt, black people typically slept about 42 fewer minutes a night than white individuals if they borrowed around $25,000 in loans. Even when black people didn't have any debt, they still got about 16 fewer minutes of sleep than white people.

"In the U.S., blacks earn less and acquire less wealth for the same amount of education," said lead study author Katrina Walsemann, a researcher at the University of South Carolina in Columbia.

"Earning less money and having less wealth may increase the strain associated with student debt," Walsemann added by email. "This may be why we found that racial disparities in sleep were greater among individuals with more student debt."

To understand the link between student debt and sleep among different racial and ethnic groups, Walsemann and colleagues analyzed survey data from almost 9,000 people born between 1980 and 1984. They did initial interviews in 1997 and conducted annual follow-up interviews through 2010, the year sleep was measured.

Half of the survey respondents had college debt, with an average loan amount of $10,176. Most had completed college by 2010, when they were 25 to 31 years old. By age 25, fewer of the participants owed money - just 36 percent of them - but their average debt amount had climbed to $17,765.

In 2010, the study participants were sleeping an average of 6.8 hours each night, but white people slept about half an hour more than black individuals.

One limitation of the study is that it relied on participants to accurately recall and report how much sleep they got, the researchers acknowledge in the Journal of Epidemiology and Community Health. They also lacked data on student debt acquired after age 25 and may not have accounted for all of the social and economic factors that could influence the amount of debt or the amount of sleep.

It also doesn't show that more debt causes poor sleep, but it does offer more evidence of the ill health effects of poverty, noted Sara Goldrick-Rab, a researcher in educational policy and financial security at the University of Wisconsin in Madison who wasn't involved in the study.

"Poverty is associated with many health consequences - including lack of sleep - and African Americans in the U.S. are dealing with a greater depth of poverty than other racial groups," Goldrick-Rab said by email.

When it comes to sleep, the average hours of rest aren't the only factor that matters, noted Alexandros Vgontzas, a psychiatry and sleep researcher at Pennsylvania State University College of Medicine.

"The true issue is not more hours of sleep but better quality of sleep which in turn means better ways to prevent, handle and cope with excessive stress," Vgontzas, who wasn't involved in the study, said by email. Sleep disparities found in the study are "a reflection of higher levels of stress in minority students," he added.