People who live further west in a time zone experience fewer days with natural morning light. As a result, they depend upon electric light to get ready for work and other business of the day. Lighter colors mean more mornings per year in light.

’Writing in the Journal of Health Economics, authors Osea Giuntella of the University of Pittsburgh and Fabrizio Mazzonna of Università della Svizzera Italiana took an innovative slant on the effect of position in a time zone on health and economics. They were interested in something called “social jet lag.”

The idea is that given the constraints of modern life, most people are out of sync with their natural circadian rhythms, which should follow the sun. Instead, we use electric light to synchronize most of our societal activities regardless of where the sun is at in its course through the heavens.

The conflict is that the primordial cycle of light and dark from the sun is deeply embedded within our evolutionary past as coded in our DNA; we have a “built-in” biological time for body temperature, hormone levels, sleep, and much more, that cycles very close to 24 hours.

Modern society requires synchronization in such things as school start times, work times and television watching times. All of these can desynchronize our social activity from our biological time. There is mounting evidence that chronic circadian rhythm disruption leads to several serious diseases as well as depression and mood disorders. On a societal level, the economic impact may also be large.

Lefties of a boundary healthier than righties?

As a test of this idea, Giuntella and Mazzonna predicted that at the boundaries between time zones within the United States, people on the left side of the boundary would be healthier than people on the right side, and the economies stronger; the left side would be the eastern extreme of one time zone, and the right side would be the western extreme of the adjacent time zone. The sun sets about an hour later on the right side.

Their primary unit of analysis was the county. They used data from the Centers for Disease Control and Prevention and from the U.S. Census, as well as information on sleep duration and quality from two national surveys. They did several different analyses, one of which was to group counties within 100 miles of the time zone boundary into two groups, one on the left side and one on the right side. They then compared the two groups for health outcomes.

As they predicted, there were discontinuities between counties on either side of time zone boundaries in sleep and in risk of obesity, diabetes, heart disease and breast cancer. In each case, counties on the right side of the boundary did worse: shorter sleep and higher risk of disease. They then calculated an overall composite health index using the diseases cited above, and it, too, was lower in the counties on the right side. They ascribe their findings to the later clock time of sunset on the right side of the boundary.…’

Via The Conversation