Loss of sleep is linked to health risks from diabetes to dementia. Now, a study in the journal "Sleep" finds Americans, especially blacks and Hispanics, are getting even less sleep than five years ago.

Researchers found a 4-percent rise in the number of people between 2012 and 2017 who slept less than six hours per day.

That's one-third of the almost 400,000 adults from the National Health Interview Survey whose self-reported sleep patterns researchers analyzed.

Lead author Connor Sheehan, a demographer at Arizona State University's T. Denny Sanford School of Social and Family Dynamics, saw a more pronounced increase among Hispanics and blacks, who already had higher risk of sleep loss before 2013.

"And we found that this risk increased — so, the gap increased over time; the inequality between whites and people of color got larger," he said.

Sheehan expressed concern that such disparities could exacerbate social and health inequalities.

From 2004 and 2017, the likelihood of shorter sleep times increased 6.5 percentage points among blacks and 7 percentage points for Hispanics. Whites showed only a two percentage point uptick.

Although the study did not track causes, previous research links sleep deficits to stress over economic insecurity, societal tensions and increased usage of devices such as smartphones, especially in bed.

In addition, Hispanics and blacks face stress associated with race-related discrimination, which prior research also links with poor sleep.

The National Sleep Foundation recommends most adults get 7-9 hours of sleep daily.