02/02/2026
Could early morning sunlight be a secret weight loss tool?
A fascinating study published in PLOS ONE found something unexpected: people who got most of their bright light exposure in the morning had significantly lower BMIs than those who got light later in the day.
Interestingly, this held true even after researchers controlled for sleep duration, how much people ate, and their physical activity levels.
For every hour that someone's average light exposure was delayed, their BMI increased by 1.28 units. So if you typically get your brightest light at noon versus 8am, that four-hour delay could translate to roughly 5 BMI points.
Researchers think the mechanism involves your body's internal clock. When light hits specialized cells in your retina each morning, it signals your brain's master clock to coordinate metabolism throughout your body. This affects how your liver and fat cells process glucose and store energy.
People who miss this morning light signal may end up with misaligned circadian rhythms, which can throw off metabolic processes even when diet and exercise stay the same.
It's an intriguing connection that suggests timing your light exposure might matter as much as what you eat.