It turns out that living on the wrong side of a time zone’s boundary can have negative consequences on a person’s health and wallet, according to new research.

The culprit? More natural light in the evening hours.

To understand the study, co-authored by Osea Giuntella of the University of Pittsburgh and Fabrizio Mazzonna of the Universita della Svizzera Italiana, it is important to understand how time zones affect local sunset times. Traveling east to west, sunrise and sunset times get later, as the map above shows.

Panama City, Fla., for instance, is located on the far eastern end of the Central time zone, while Pecos, Texas, sits on the far western side. This week, the sun set in Panama City about 7:12 p.m. Central time. In Pecos, it set more than an hour later, at 8:25 p.m.

Sunset is a powerful biological trigger: The fading of natural light causes the body to release melatonin, a hormone which induces drowsiness. As a result, people on the eastern side of a time zone, where the sun sets earlier, tend to go to bed earlier than those on the western side. The data below, derived from about 1 million users of the now-defunct sleep tracker Jawbone, illustrates this point, showing how bedtimes shift from east to west, with a sharp reset happening once you cross into a new time zone.

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