What sleep deprivation does to your brain and body

Fatigue, brain fog, irritability, headaches, and palpitations are not isolated symptoms. Doctors report seeing these especially among young professionals who stay up past midnight juggling project deadlines and household responsibilities, working long shifts, where restorative sleep feels impossible. Over time, this continuous lack of rest gradually alters the brain and body, affecting cognition, mood, metabolism, and long-term health.

A study published in Nature Neuroscience helps explain why this happens. Researchers found that when you are sleep-deprived, your attention does not fade simply because you feel tired. Instead, the brain and body begin to shift together: brain activity changes, pupils subtly constrict, blood flow patterns alter, and even the flow of cerebrospinal fluid starts pulsing differently. These changes align with moments when focus slips

Sleep and brain

Sleep is far more than rest. Karthik Madesh Ratnavelu, ENT and head & neck surgeon at SIMS Hospital, Chennai, explains that deep non-REM sleep, or slow-wave sleep (SWS), is the most restorative stage of sleep, happening mainly in the first half of the night, which he describes as “night shift mode” for the brain.

During this phase, the glymphatic system or the brain’s waste-clearance network, flushes out metabolic byproducts such as beta-amyloid, excess neurotransmitters, and proteins.

Benhur Joel Shadrach, sleep medicine physician at Rela Hospital, adds that during deep sleep, tiny spaces in the brain expand, letting cerebrospinal fluid flow through Aquaporin-4 channels to clear out toxins and when sleep is disrupted, waste accumulates, glial inflammation increases, and the risk of neurodegenerative diseases rises.

Impact in health

Chronic sleep deprivation impairs frontal brain networks responsible for attention, focus, and decision-making. Dr. Ratnavelu explains that people may experience micro-sleeps or brief moments of lost awareness. Dr. Shadrach describes this as mental haze, where slowed neural communication and short-term memory lapses reduce comprehension and decision-making ability

Sleep loss can also disrupt main hormonal systems. Shubha Subramanian, neurologist, Kauvery Hospital, Chennai, explains that the hunger hormone called ghrelin, rises, while leptin, which signals fullness, falls, encouraging nighttime snacking and overeating. Also, the stress hormone –cortisol, stays elevated in the evening, and can worsen anxiety and irritability, whereas the growth hormone and testosterone decrease, slowing tissue repair and reducing energy. Insulin sensitivity too, drops, increasing the risk of weight gain, metabolic syndrome, and type 2 diabetes.

Over time, sustained cortisol and sympathetic nervous system activation strain the heart, raising the likelihood of hypertension, heart attacks, and strokes. Sleep deprivation also affects reproductive hormones and libido, leaving adults more prone to anxiety, irritability, and burnout.

Limits of catch-up sleep

Many try to compensate their weekday loss of sleep with longer sleep time during weekends. While this may temporarily reduce fatigue and lower cortisol, it cannot fully erase the effects of lack of sleep, hormonal imbalance, or metabolic disruption. Adults require consistent seven to eight hours of nightly sleep for complete cognitive and physical health.

Experts stress that structured sleep hygiene — consistent sleep-wake times, limiting evening screen exposure, avoiding late caffeine, and prioritising restorative rest are important. This helps your brain stay sharp, balances hormones and metabolism, supports heart health, and strengthens your body’s overall well-being.

Published – February 20, 2026 06:00 am IST