Bryan Johnson says, ‘a single night of 4 hour sleep can drop insulin sensitivity by 25%’, suggests ways to prioritise it for longevity

Many people routinely cut back on rest to meet work deadlines, manage household responsibilities, or simply scroll through their phones late into the night. Lower insulin sensitivity doesn’t just affect energy levels; over time, it can increase the risk of metabolic disorders and weight gain.

Johnson also shared his personal checklist for better sleep and healthy ageing: “Prioritise 7.5+ hours of sleep, eat at least 4 hours before bed, no coffee 6 hours before bed, no heavy exercise 4 hours before bed, keep your room dark and cool, avoid blue light and screens 1–2 hours before sleep.”

 

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Bryan Johnson mentioned that ‘a single night of 4-hour sleep can drop insulin sensitivity by 25%.’ How accurate is this figure?

Dr Himika Chawla, senior consultant, Endocrinology and Diabetology at PSRI Hospital, Delhi tells indianexpress.com, “The statement is largely accurate and supported by several studies. Even one night of restricted sleep can significantly reduce insulin sensitivity — the body’s ability to use glucose effectively. This happens because lack of sleep disrupts the balance of hormones such as cortisol and growth hormone, which play a key role in glucose metabolism.” 

She adds that elevated cortisol levels increase blood sugar, while reduced insulin activity forces the pancreas to produce more insulin to maintain normal levels. Over time, this can lead to insulin resistance, weight gain, and metabolic disorders.

From a medical perspective, how do these habits influence the quality and depth of sleep?

Eating too close to bedtime can raise body temperature and blood sugar levels, Dr Chawla notes, making it harder for the body to transition into a restful sleep state. A gap of four hours allows digestion to complete and promotes better melatonin release, which supports deeper sleep. 

Similarly, caffeine stimulates the central nervous system and can stay active in the body for up to six hours, delaying sleep onset and reducing REM sleep. Dr Chawla states, “Heavy exercise close to bedtime also increases adrenaline and heart rate, making it difficult for the body to relax. Avoiding these triggers helps maintain a natural circadian rhythm and improves both the quality and duration of sleep.”

Adjustments to improve sleep quality and support metabolic health

For those who can’t get full-length sleep, maintaining sleep consistency is key. Going to bed and waking up at the same time daily stabilises the body clock. Creating a dark, cool, and quiet environment helps induce deeper sleep cycles. 

“Limiting screen time before bed, avoiding alcohol or caffeine late in the day, and practising relaxation techniques like deep breathing or meditation can also enhance sleep quality. Even short daytime naps (20–30 minutes) can help restore alertness and metabolic balance when nighttime sleep is insufficient,” concludes Dr Chawla.

DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.