A new five-year study is examining whether the time zone you live in could be silently disrupting your body's internal clock in ways that increase serious disease risk. Researchers at Fred Hutchinson Cancer Center have received nearly $1 million in funding from the American Cancer Society to investigate whether "solar jet lag" may be driving cases of hepatocellular carcinoma (HCC), the most common form of liver cancer.

What Is Solar Jet Lag and Why Should You Care?

Most people think of jet lag as something that happens when you fly across time zones. But solar jet lag is different, and it affects millions of people who never leave their home region. It occurs when your internal circadian rhythm, or body clock, becomes misaligned with the sun's actual schedule based on where you live within your time zone.

Here's a concrete example: Seattle and Spokane are both in the Pacific Time Zone, yet sunrise and sunset occur more than 20 minutes later in Seattle because it sits on the western edge of the time zone. This seemingly small difference means people in Seattle experience chronic circadian misalignment compared to those in Spokane, even though they follow the same clock.

"Solar jet lag is defined as the difference in light exposure experienced by people based on their geographic location within a time zone," explained Dr. Trang VoPham, an epidemiologist at Fred Hutchinson Cancer Center's Public Health Sciences Division.

Dr. Trang VoPham, Epidemiologist at Fred Hutchinson Cancer Center

The problem intensifies for shift workers and night-shift employees, whose sleep schedules are completely reversed from the sun's natural rhythm. This type of circadian disruption has been linked to serious health consequences, including metabolic dysfunction, obesity, diabetes, and now potentially liver cancer.

How Does Circadian Disruption Damage Your Liver?

Your liver isn't just a passive organ that processes toxins. It has its own internal circadian clock that regulates when and how efficiently it performs critical functions. When your body clock is out of sync with the actual time of day, your liver's timing system breaks down.

Animal studies have shown that circadian disruption promotes both the development and progression of liver disease and hepatocellular carcinoma. The liver metabolizes food most efficiently during your biological day, meaning that eating and sleeping at the wrong times relative to the sun's schedule forces your liver to work against its natural rhythm. Over time, this chronic stress on liver function may contribute to disease risk.

The connection runs deeper than just meal timing. Circadian disruption interferes with clock-controlled cellular processes and molecular pathways throughout the liver, which researchers believe contributes to metabolic dysfunction-associated steatotic liver disease (MASLD), a condition that significantly increases hepatocellular carcinoma risk.

Ways to Counteract Solar Jet Lag and Support Your Circadian Health

• Light Exposure Management: Deliberately expose yourself to bright light in the morning and limit light exposure in the evening, especially blue light from screens. This helps reset your internal clock to align with your geographic location's actual sunrise and sunset times.
• Sleep Environment Optimization: Use eye masks during sleep to block unwanted light exposure, particularly if you work night shifts or live on the western edge of your time zone where sunrise comes later than your work schedule suggests.
• Meal Timing Alignment: Eat your largest meals during daylight hours and avoid eating late at night, since your liver metabolizes food most efficiently during your biological day. This reduces the metabolic stress caused by circadian misalignment.
• Consistent Sleep Schedule: Maintain a regular sleep-wake schedule that aligns as closely as possible with the actual sunrise and sunset in your geographic location, rather than following arbitrary clock times.

Dr. VoPham's team plans to design both behavioral interventions and public health policy recommendations to help people mitigate solar jet lag's effects. The research will pair electronic health records from the Veterans Health Administration with a new high-resolution geospatial light exposure model to quantify the actual association between solar jet lag exposure and hepatocellular carcinoma risk.

The encouraging news is that solar jet lag is what researchers call a "modifiable exposure," meaning people can take concrete steps to reduce its impact on their health. Unlike genetic risk factors or past exposures you cannot change, your daily light exposure and sleep timing are behaviors you can actively manage.

As this groundbreaking research unfolds over the next five years, it may reshape how we think about the relationship between geography, circadian health, and disease prevention. For now, the takeaway is clear: your location within your time zone matters more than most people realize, and paying attention to when the sun actually rises and sets where you live could be an important part of protecting your long-term health.