A new study has found that the quality of Americans’ sleep varies depending on region.

Researchers published their findings in the journal Sleep Health and found that across the nation there are 84 “hotspots” where there are higher levels of people getting insufficient sleep and 45 “coldspots” where there are lower levels.

“Sleep is more than a physiologic process. Understanding the context of sleep will help us understand how and where to target our efforts,” said Michael Grandner, the study’s lead author and an assistant professor of psychiatry at the University of Arizona. “It is possible that improving sleep at the population level will be key to improving the public health.”

The survey included 432,000 people and asked them: “During the past 30 days, for about how many days have you felt you did not get enough rest or sleep?”

Those who cited poor sleep on fewer than 15 days were placed in one group, and those who slept poorly on 15 or more days were placed in another. The study said: “The cutoff of 15 days was chosen to mirror the diagnostic criteria for insomnia.” It said that symptoms are “clinically relevant” if they exist for approximately half of a given stretch of nights.

The responses were divided up by county, to establish the prevalence of insufficient sleep at the county level. These estimates were evaluated to discern areas that have unusually high or low sleep levels, the so-called “hotspots” and “coldspots”.

The counties with the highest levels of insufficient sleep were at the intersection of Kentucky, Tennessee, West Virginia and Virginia. More than half of the counties that were deemed “hotspots” fell within that region. The study lists its “most important limitation” as its inability to “explore reasons for this geographic variation”. Ohio, Texas, and Missouri also saw high numbers of “hotspots”.

Unlike those who get insufficient amounts of sleep, those who reported getting enough sleep are not as concentrated in one place. The study found no “coldspots” that were comparable with the intensity of the “hotspots”.

There were smaller aggregations of those who reported getting enough sleep in Texas, northern Virginia, and the northern midwest. Of the 45 “coldspots” identified, 42 had rates of sleep difficulty at or below 20%.

The study used data from the Center for Disease Control and Prevention’s 2009 Behavioral Risk Factor Surveillance Survey. The researchers used data from 2009 because they started their analyses in 2010 when it was released. But they “hope to follow this up with more recent data,” according to Grandner.

Lauren Hale, an associate professor of Preventive Medicine at Stony Brook University and the editor-in-chief of Sleep Health, said that she “would not expect big changes in the sleep patterns between 2009 and 2014”.

Ten of the counties reported rates of 0% sleep difficulty. Grandner accredits this to “a major limitation” of the data since some counties were only represented by a few people. He explained that “the fewer the people in each county, the more imprecise the estimate will be”.

The researchers looked into numerous social and demographic factors to see if there was any correlation as to why some people sleep less in certain regions of the US. Their analyses included age, sex, education, obesity, overall physical and mental health and more. No clear pattern emerged for “coldspots”. But they found that those who are “relatively younger individuals of lower socioeconomic status and poorer health were more likely to live in hotspot counties”.

The study says the data provided can be used by members of the public and health authorities “to discern the public health burden of sleep disturbance relative to geography”. But they explained that further investigation of what causes the “geographic variability” needs to be explored.

“This is just a first step,” Gardner said. “Once we identify where these resources are directed, we can dig deeper to understand why these particular regions are hardest hit and what can be done about it.”