At the Longevity India 2025 longevity India conference in Bengaluru, Dr. Satchidananda of the Salk Institute raised a key question: could the timing of eating, rather than just food choices, impact healthier ageing?
Published Mar 14, 2025 | 8:00 AM ⚊ Updated Mar 14, 2025 | 1:32 PM
sleep disruption can cause break in circadian rhythm
Synopsis: As World Sleep Day nears, experts emphasise that it’s not just about sleep duration but timing, eating habits, and light exposure. At the Longevity India 2025 conference in Bengaluru, Dr. Satchidananda of the Salk Institute explored how when you eat could impact ageing. He identified four key factors affecting long-term health: infectious diseases, metabolic and chronic conditions, brain health, and injuries
As World Sleep Day approaches, one of the biggest lessons in health and longevity isn’t just about how much you sleep—but when you sleep, eat, and expose yourself to light. Could your daily routine be silently ageing you?
At the three-day Longevity India 2025 conference hosted by the Indian Institute of Science (IISc) in Bengaluru, leading scientists worldwide gathered to discuss cutting-edge research on healthy ageing. At the conference, Dr Satchidananda (Satchin) Panda, a leading circadian biologist from the Salk Institute in California, posed a fascinating question: What if the key to a longer, healthier life isn’t just what you eat, but when you eat?
Karnataka Health Minister Dinesh Gundu Rao inaugurating IISc’s Longevity Indian Conference 2025 held on Monday
Speaking about why one can’t live a long healthy life, he says, there are four major reasons: Infectious diseases, metabolic and chronic disease, brain health conditions and injuries.
For years, we’ve been told to focus on diet and exercise to stay healthy, but Dr Panda’s research suggests that one of the strongest indicators of good health is a well-regulated circadian rhythm—the body’s internal clock that controls sleep, digestion, and metabolism. “The best biomarker of health is a strong circadian rhythm—getting seven to eight hours of sleep, having a regular bowel movement, and engaging in daily physical activity. These are things you can monitor yourself,” he said.
He explains that nearly every gene in our body follows a natural rhythm, fine-tuned by millions of years of evolution to sync with the rising and setting of the sun. However, modern life—late-night screen time, erratic meal schedules, and artificial lighting—is throwing these rhythms into chaos, putting us at risk for obesity, diabetes, heart disease, and even neurodegenerative conditions.
Dr Panda emphasises that most adults require between six and a half to seven and a half hours of sleep for optimal health. This range is associated with lower morbidity and increased life expectancy.
He also notes that the timing of sleep is crucial, as it aligns with our body’s natural circadian rhythms. Disruptions to these rhythms, such as irregular sleep patterns, can lead to various health issues, including metabolic dysfunction and reduced cognitive performance.
10 PM: If someone goes to sleep around this time, melatonin levels are at their peak, helping the body transition into sleep.
12 AM – 2 AM: Deep sleep occurs, crucial for physical recovery and memory consolidation.
4 AM: The body’s temperature begins to rise as it prepares for wakefulness.
6 AM: Melatonin levels start dropping, signalling the body to wake up.
6-8 AM: Cortisol, the alertness hormone, begins to rise, helping the body wake up naturally.
8-10 AM: Bowel movements are most likely to occur due to peak morning cortisol levels.
10 AM – 12 PM: Peak insulin sensitivity occurs, making this a good time for a balanced meal.
12 PM – 4 PM: High alertness and cognitive function peak, making it the best time for focused work.
4 PM – 6 PM: Muscle performance peaks, making it an ideal time for intense physical activity.
6 PM onwards: Melatonin production gradually begins, preparing the body for sleep.
Dr Satchidananda explains the circadian clock at IISc Bengaluru.
Dr Satchidananda argues that one should attempt to sleep at the same time and wake up the same time every day. Meanwhile, he says broken circadian rhythm can disrupt this internal clock. Citing an example he says, “Suppose one stays awake for extra two hours tending to office work or any other chore then there is a host of diseases that can set in,”
He explains, when we disrupt our sleep, we feel terrible the next day. If this pattern continues, our internal clocks become misaligned, increasing the risk of various health conditions, including ADHD, asthma, diabetes, obesity, depression, anxiety, and even cancer. This highlights the crucial role of the circadian clock in maintaining overall health.
For the past two decades, research has shown that each morning, when we open our eyes, bright light signals the retina, which then resets a small region in the brain responsible for the body’s master circadian clock. This clock aligns with the day-night cycle and sends hormonal signals to regulate other functions in the body. Surprisingly, it’s not just the brain that has a clock—every organ and even individual cells have their own internal rhythms. The brain acts as a central coordinator, synchronising these clocks to regulate daily patterns in behaviour, physiology, and metabolism.
Interestingly, circadian rhythm also helps in how we use nutrients, manage energy, repair damaged DNA, remove toxins, and fight infections. It also affects how our cells communicate, release important substances, and maintain protein balance. When our circadian rhythm is well regulated these functions work effectively. However, disruptions in the rhythm can speed up ageing and increase the risk of diseases.
Dr Panda says that his research has shown that modern lifestyles that cause circadian rhythm disruption majorly includes shift work, jetlag, and social jetlag. Citing examples he says, “According to the international Labor Organisation, staying awake for more than two hours of normal sleep time and engaging in some task/work between 10 pm and 5 am for 50 nights in a year, the body will take two days to come back to normalcy. Similarly, in social jetlag, where there is change in sleep/wake time (and sleep duration) by less than two hours between workdays and off days or party days/wedding etc then the circadian rhythm is broken for three to four days.
“Frequent fliers travelling over two or more time-zones within a day can actually disrupt circadian rhythm so bad that it takes nearly 12 days to re-adjust,” he adds.
The final one is second hand shift workers. In India, there are about 30 percent of working adults who can be termed as shift workers. He says atleast 80 percent of adults at some point in time undergo atleast 5-7 years of being shift workers. Spouses and family members of shift workers also lose their sleep.
Dr Panda advocates for Time-Restricted Eating (TRE)—a form of intermittent fasting where food intake is limited to an 8-10 hour window each day. The benefits? Lab studies, he says, showed it can help prevent obesity, diabetes, liver and kidney disease, and even some cancers. Even more exciting, TRE appears to slow ageing and improve muscle mass in older adults.
Human studies are beginning to mirror these findings. “Our ancestors weren’t eating at all hours of the day and night,” Dr Panda pointed out. “They ate when the sun was up and fasted overnight. Aligning our meals with our body’s internal clock may be one of the simplest, yet most powerful ways to protect our health,”
He explains that one must avoid eating atleast one hour after waking up and also have a consistent time for breakfast. He says, a 8-9-10-11-12 hour window of fasting works very well.
Meanwhile he suggests one must not eat heavy calories atleast two to three hours before bed.
It’s worth noting that Dr Panda’s research extends beyond just food. Light exposure plays a huge role in regulating sleep quality. “Bright light in the morning can improve mood and focus, while blue light at night can disrupt sleep and increase the risk of depression,” he said.
“Just as we time our meals, we should also time our light exposure for better health.”
He says, as soon as we wake up, exposure to bright natural light helps synchronise our master circadian clock. This signals the brain to regulate hormones and bodily functions in alignment with the day-night cycle. Ideally, we should get at least 30–60 minutes of sunlight in the morning to support alertness and energy levels.
Meanwhile, exposure to artificial blue light from screens (phones, TVs, laptops) after sunset or within two hours of bedtime can suppress melatonin production, delaying sleep onset and disrupting the body’s natural rhythms. He advises minimising screen use in the evening or using blue light filters.
As bedtime approaches, switching to warmer, dim lights, he explains, helps signal to the body that it’s time to wind down. This supports melatonin release and prepares the body for restful sleep.
Maintaining a regular sleep schedule and aligning with natural light exposure patterns helps optimise the circadian rhythm, reducing the risk of metabolic disorders, mental health issues, and other chronic diseases.
Hospitals have even started adjusting lighting conditions for patients, and the results are promising—faster recovery times, better sleep, and improved mental well-being.
As Dr Panda put it, “Health isn’t just about what you do—it’s about when you do it.”
(Edited by Ananya Rao)
