Sleep doesn't always come for the weary - and if you're African-American, Hispanic, or Asian, it may be even harder for you to drift off at night.

There's a burgeoning crop of studies that suggest minority groups have higher rates of disordered sleep than Caucasians. And given that lack of sleep has been linked to a host of health problems, including cardiovascular disease and obesity, understanding how ethnicity may affect sleeping patterns may go a long way toward explaining differential rates of disease.

 A report in April from the U.S. Centers for Disease Control and Prevention found that 30% of employed adults slept less than six hours in a 24-hour period. Minority workers had much higher rates of short sleep periods -- nearly 40% of black workers and 33% of Asian workers reported sleeping less than six hours in a night, as compared to 28% of white workers.

"Rotating workers forward from evening to night shifts rather than backwards from night to evening shifts makes it easier for circadian rhythms to adjust so that workers can sleep during their rest times," the CDC explained.

A more recent study forthcoming in the journal Clinical Medical Research found racial trends in sleep problems among a sample of more than 30,000 customers of Kaiser Permanente Northern California.

Kaiser Permanente researcher Nancy Gordon found that across all ages, blacks, Latinos and Filipinos of both genders are significantly more likely than non-Hispanic whites to get less than seven or six hours of sleep per day than whites.

"Among those who usually try to get enough sleep, Blacks, Latinos, Filipinos, and Chinese are significantly less likely than non-Hispanic Whites" to get 7 hours of sleep per day, "with Blacks and Filipinos least likely," Gordon wrote.

Some experts say that people who feel more in control of their lives, and hence more secure, are able to have better sleep patterns

Sleep differences can also vary between races very early on. In a 2011 study published in the Journal of Family Psychology, Stony Brook University Medical Center researcher Lauren Hale and her colleagues looked at language-based bedtime routines - when parents read books or sing songs with their children before bed.

"Black, less-educated, single-mother, and low-income families have significantly lower reported use of language-based bedtime routines than their counterparts," the authors wrote.

These kinds of routines can help children feel safe at night, making it easier for them to fall asleep, according to the researchers.

"We're not at a point where we can say for certain is it nature versus nurture, is it race or is it socioeconomics," University of Pennsylvania sleep researcher Michael A. Grandner told the New York Times on Monday. However, "there is a unique factor of race we're still trying to understand."