What if one of the clearest signs of health is something you can feel every day? In this program, Satchidananda Panda, Ph.D. (Salk Institute), describes circadian rhythm as a built-in 24-hour daily rhythm “written in our DNA,” and he calls it a powerful biomarker of whether we’re healthy. He connects that internal timing system to three foundations of health—sleep, nutrition, and exercise—and emphasizes that they influence each other in a tight loop.
A big part of the story is light and darkness. Panda explains that our eyes contain light-sensing pathways that are especially sensitive to blue light, and he puts numbers on what “bright” really means: typical indoor lighting can feel intense while still being around the hundreds to low thousands of lux, while stepping outdoors can deliver far more. He notes that about 10,000 lux for an hour is a common benchmark used for light therapy, and that even a cloudy day outside can reach that level. For evenings, he recommends dimming light to under about 20 lux when possible, ideally with no blue light, and he points to phone “night shift/night light” features as one practical tool.
Food timing is the other major lever. Panda discusses time-restricted eating (also called time-restricted feeding), often grouped in popular culture under “intermittent fasting.” He describes experiments in which time-restricted feeding improves health in mice, and he explains why “eight hours eating, 16 hours fasting” became the headline—then adds that his team systematically tests different schedules (8, 9, 10, 11, 12 hours) and finds that 8–10 hours of eating is “good enough,” including a 10-hour eating window with a 14-hour fast. He also shares practical guidance: after waking, he recommends avoiding food for at least one hour, and he suggests keeping the daily eating window consistent—ideally around 10 hours, with 11–12 as an upper limit, because eating too close to bedtime is bad for blood glucose control and sleep.
He ties these ideas back to daily rhythms we can actually manage: dim light in the hours before bed to support melatonin release, avoid late timing that pushes eating into the night, and pair daytime movement with daylight when you can—he specifically mentions late-afternoon brisk walks or outdoor exercise. Panda also describes tools to better understand when people actually eat, and he points to “chronomedicine” as a growing field that examines how timing affects treatments.
Taken together, Panda suggests these timing-based habits may support better metabolic health and everyday functioning by reinforcing the body’s natural cycles of activity, repair, and rest. He connects circadian disruption to higher risk for chronic conditions and frames consistent light exposure, sleep timing, and a regular eating window as practical ways to reduce strain on the system and support healthier aging over the long term.
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