Light-emitting devices and high stress levels could be contributing to sleep deficits among Americans, especially minorities, reports Science News.

Nearly one-third of American adults sleep less than six hours each night, a broad new survey shows.

Among nearly 400,000 respondents to the annual National Health Interview Survey, 32.9 percent reported this short sleep in 2017 — up from 28.6 percent in 2004 when researchers began noticing a slight drop in sleep time. That’s a 15 percent increase representing “more than 9 million people, which is about the population of New York City,” says coauthor Connor Sheehan, a sociologist at Arizona State University in Tempe.

Analysis of the annual survey results?—?accounting for the U.S. population’s age distribution as well as respondents’ marital status, income, employment and lifestyle?— suggests people have been sleeping significantly less from 2013 onward, especially black adults, the researchers report online November 17 in Sleep. In 2017, 40.9 percent of black Americans were likely to report short sleep, as were 30.9 percent of whites and 32.9 percent of Hispanics, the researchers calculate.