Before standard time zones, cities set clocks based on the time of local sunrise and sunset…resulting in more than 300 different “time zones” across the US! Having official time zones solved the confusion over what’s the correct time, but it has led to an unexpected health consequence for people in a certain section of each zone.

Researchers at the Center for Environmental Therapeutics (CET)in New York City looked at 1,510 adults, ages 22 to 70, living in the northern half of the US who responded to an online survey on winter depression. They found that winter depression symptoms were higher the farther west in each zone—30% higher on the western edges compared with the eastern edges. Earlier research by the same team had found that winter depression symptoms are higher—more than double—in the northern half of the country compared with the southern half.

Combining data from both studies, the highest risk for SAD symptoms was in western zones of Michigan, the Dakotas, Montana and Idaho.

Here Comes the Sun…

The morning light of sunrise sets your biologic clock, which establishes circadian rhythm and the timing of such things as wakefulness and sleepiness. Your biologic clock also affects mood and health. When the biologic clock gets out of synch with daylight and darkness, it leads to fatigue, irritability, trouble concentrating, weight gain and depression—the symptoms of seasonal affective disorder (SAD).

It’s well-known that risk for SAD increases when daylight hours are short, such as during winter months, especially at northern latitudes. But while everyone at a particular latitude gets the same total sunlight, the artificially established official time across a wide longitudinal distance means that some people are not getting an appropriate amount of sunlight at the time that their biologic clock expects it.

For example: Say, “sunrise” is 7 am in the Eastern Standard Time (EST) time zone. On the east coast of Maine, at 7 am the sun is indeed starting to send out brightening rays and revving up circadian rhythms. But in Indianapolis, on the western edge of the same time zone, it’s still dark—and biologic clocks are insisting that it’s still time to sleep. And in Chicago, only 100 miles away but on the eastern edge of the Central Time zone, “official” sunrise is an hour later—when the sun actually is rising in Chicago.

And the recent extension of Daylight Saving Time, to last from early March to November, just adds to the circadian confusion.

Other Health Risks

Besides putting you at risk for depression, having your biologic clock chronically out of synch also affects other body functions, including temperature regulation and hormone production…and may increase risk for cancer. A National Cancer Institute 12-year study of four million adults found that for every five degrees of longitude farther west within a time zone, risk for any type of cancer increased 3% for men and 4% for women. The researchers suspect that physiologic changes caused by disrupted circadian rhythm negatively affect the immune system and may contribute to the risk for cancer.

Time zones aren’t going away (nor would we want them to). But knowing about the western-edge effect can be a helpful heads-up so that you can take steps to protect your mental and physical health, such as…

• Taking a low dose of a melatonin supplement a few hours before the time you choose to go to bed can help you reset your sleep and wake time to move your biologic clock forward or backward as needed.  

• Turn on bright lights as soon as you wake up. Artificial early morning light therapy can coax your biologic clock back into sync. You may need to buy a special type of light that is very bright (10,000 lux) to simulate natural sunlight.

• Try using a dawn-simulating light in your bedroom.

• Increase your exposure to natural sunlight during the day and decrease your exposure to artificial light after dark.

If seasonal depression is a serious and recurrent issue, it may be worth considering moving to the East or South.

Learn more about SAD and light therapy by visiting the CET website, which also offers free self-assessment questionnaires to see if you’re at if risk.

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