(Reuters Health) - Black and Hispanic drivers are at twice the risk of falling asleep at the wheel compared to whites, and differences in sleep quality explain at least some of the disparity between blacks and whites, a U.S. study suggests.

Based on surveys covering nearly 200,000 adults across 35 states, researchers found that sleep-quality-related symptoms like feeling sleepy during the day, getting too little sleep and snoring accounted for about 25 percent of the disparity in drowsy driving incidents between blacks and whites, but didn't explain the higher rates among Hispanics.

More research is needed to explain and address this significant public health issue, the study team writes in the journal Sleep Health.

"We want readers to understand the public health importance of drowsy driving," said senior study author Dr. Sanjay Patel, director of the Center for Sleep and Cardiovascular Outcomes Research at the University of Pittsburgh, "and how - like many other health measures - blacks and Hispanics face a greater burden in the United States."

"While some of this may be due to poorer sleep compared to whites, much of the disparity is still unexplained. It does not, for example, appear to be due to alcohol use, risk-taking behaviors or economic barriers to health," he said in an email.

Drowsy driving is defined as operating a motor vehicle while "drowsy, sleepy, asleep, or fatigued," and drowsy drivers contribute to as many as 328,000 crashes and 6,400 deaths each year in the United States, the study authors note.

Overall, sleepiness is thought to be a factor in anywhere from 2 percent to 20 percent of all crashes resulting in fatalities or hospitalization, they add.

Past research has found that blacks and Hispanics are at higher risk than whites for drowsy driving, but less is known about why this disparity exists. Patel's team analyzed data from annual health surveys by the Centers for Disease Control and Prevention between 2009 and 2012, looking for factors that might explain the differences.

The researchers assessed participants' answers to the question, "During the past 30 days, have you ever nodded off or fallen asleep, even just for a brief moment, while driving?" They also looked at self-reported sleep problems, drinking and other risky behaviors, socioeconomic factors, health insurance status and other factors that might influence drowsy driving risk.

About 60 percent of participants were women, 6 percent were black, 7 percent Hispanic and 87 percent white. Half were 44 years or older.

After adjusting for other factors, researchers found that compared with whites, blacks had double the risk of having had a drowsy driving incident and Hispanics were 80 percent more likely to say they had one.

Whites were less likely to say they experienced daytime sleepiness while blacks and Hispanics were more likely to be uninsured and to say they did not seek medical treatment as result of high out-of-pocket costs.

Individuals who reported falling asleep while driving were younger, more likely to be male and to have a slightly higher body mass index, a measure of weight relative to height, compared to their wide-awake counterparts. They were also more likely to experience daytime sleepiness, to report higher dissatisfaction in sleep quality and to get fewer than seven hours of sleep per night.

"It is known that people of minority races are more likely to be nightshift workers, which itself is a risk factor for drowsy driving," said the study's lead author, Dr. Michael Genuardi, also of the University of Pittsburgh Medical Center. "But we were surprised that poor sleep explains some of the disparity in blacks, but not Hispanics."

"Driving while sleepy is a dangerous behavior," said Christopher Watling of the Center for Accident Research & Road Safety at the Queensland University of Technology in Brisbane, Australia, who was not involved in the study. "No single individual is immune to the effects from sleepiness and willpower simply cannot reduce the impairment from sleepiness. But importantly, fighting sleepiness to stay awake will always be a losing game."

In short, sleep is the only cure for sleepiness, he said in an email. But there are a number of things that can help reduce sleepy driving incidents.

"Utilizing an effective countermeasure like napping, consuming caffeine or even using rest breaks can reduce the likelihood of crashing. Simply considering alternatives to driving can be an important safety consideration, too," Watling said.

SOURCE: bit.ly/2rwmOfv Sleep Health, online April 5, 2018.