Sleep. It’s the one thing of which everyone wants more, but consistently fails to get enough. Though a recent study proves there’s a factor keeping us from getting more shuteye that may be entirely out of our control.

According to research published this month in the Journal of Health Economics, living on the wrong side of a time zone can negatively affect how much sleep a person gets and lead to a decrease in their overall health. Specifically, the western side of a time zone – where the sun sets later than in the East.

America’s time zones are divided by hard borders. Whether you live in West Quoddy Head, Maine (the easternmost point in the Eastern time zone), or Ontonagon County in Michigan (the westernmost point), the time will be exactly the same. However, on April 23, the sun will set at 7:23 p.m. in West Quoddy Head – whereas it sets at 8:56 p.m. in Ontonagon County. That’s over an hour and a half of extra sunlight.

Why does that matter? Sunlight is a biological trigger, and when the sun goes down, the body releases the sleep-inducing melatonin hormone. With an earlier sunset, the body naturally becomes tired sooner, leading to an earlier bedtime.

“Individuals on the late sunset side of a time zone boundary are more likely to be sleep deprived, more likely to sleep less than 6 hours, and less likely to sleep at least 8 hours,” wrote the authors of the Journal of Health Economics study. “The effects are larger among individuals with early working schedules and among individuals with children of school age.”

Other studies back this up: The American Time Use Survey by the Bureau of Labor Statistics found that those living in a later sunset area of a time zone go to bed an average of 19 minutes later than those in earlier sunset areas.

Naturally, the western areas of time zones showed higher rates of health issues commonly associated with sleep deprivation. Those living in late-sunset areas were 11% more likely to be overweight and 21% more likely to be obese. Heart attack rates increased by 19%. There were even economic differences: tired people tend to be less productive, and wages were 3% lower in western areas of time zones.

There was one ray of light for those living in western areas of time zones. With extra sunlight, people tend to enjoy the time they spend awake a little bit more.

“Individuals may derive more utility from enjoying leisure time with more natural light in the evening,” the study wrote.