Night Shift Work and Increased Cancer Risk: Understanding the Causes

When the rest of the world turns off the lights, many people clock in for work. Nurses, security staff, call-centre executives, writers, and factory workers know the drill well; coffee at midnight, meals at odd hours, sleep stolen during daylight. What feels like a lifestyle adjustment, however, is actually a biological rebellion. The human body is designed to follow the sun. Darkness signals rest, repair and hormonal balance. Light signals activity. Night shifts reverse this ancient programming, and over time, the consequences can be far more serious than fatigue. Working under artificial light at night suppresses melatonin, the hormone that regulates sleep and supports immune defence. “Melatonin is produced only in darkness,” explains Dr Nambiraj Konar, Consultant and Head, Anaesthesiology and Pain Medicine, HCG ICS Khubchandani Cancer Centre, Colaba. “Its reduction weakens natural killer cells, which play a key role in identifying and destroying abnormal or cancerous cells.” This disruption doesn’t stop at sleep. Cortisol, insulin and appetite hormones also fall out of sync. The result is inflammation, insulin resistance, weight gain and a metabolism that struggles to function efficiently. Over months and years, this internal chaos increases vulnerability to chronic disease. Also read: Doctor says these 3 medicines can save a heart attack patient Night work itself does not directly cause cancer, but long-term circadian disruption creates a fertile ground when combined with other risk factors. “Poor cellular repair at night and increased oxidative stress allow damaged cells to survive longer than they should.” shares Dr Konar. Research has shown links between prolonged night duty and certain cancers, particularly those influenced by hormones and digestion. Breast cancer The strongest association seen so far. Low melatonin leads to higher oestrogen levels, encouraging abnormal breast tissue growth. Prostate cancer Hormonal imbalance and impaired DNA repair at night may increase risk in men working night shifts for years. Colorectal cancer Irregular digestion, late-night meals, chronic inflammation and oxidative stress heighten vulnerability. “Night shift work forces the body to function against its circadian rhythm, which controls metabolism and glucose regulation,” says Dr Vimal Pahuja, MD, Associate Director, Internal Medicine and Metabolic Physician, Dr LH Hiranandani Hospital, Powai. “When eating and activity happen at the wrong time, insulin resistance, obesity and metabolic syndrome become far more likely.” Timing matters as much as food quality. Heavy meals at midnight and constant snacking disrupt insulin balance, increasing the risk of type 2 diabetes. Hormonal balance also flatten. “Cortisol becomes erratic, leading to visceral fat, high blood pressure and insomnia. Women may see worsening PCOS symptoms, irregular periods and fertility issues, while thyroid rhythms may slow, causing sluggish metabolism.” he says. Also read: Rare medical condition leaves Archana Puran Singh’s hand permanently affected, know all about it Protecting health when night duty is unavoidable Doctors stress that risks can be reduced with mindful habits. “Night workers should aim for time-restricted eating within an 8–10 hour window, regular post-shift sleep, consistent physical activity and moderate caffeine use,” advises Dr Pahuja. Regular monitoring of blood sugar, lipids, blood pressure and hormones is equally important. Night shifts may be necessary, but understanding their hidden impact allows workers to reclaim some control. FAQs on how working late in night affects health: How does working late at night affect the body? It disrupts the natural sleep–wake cycle, affecting hormones, metabolism, and recovery. 2. Can late-night work impact mental health? Yes, it can increase stress, anxiety, irritability, and reduce focus and productivity. 3. Does working late affect heart and metabolic health? Chronic late-night schedules are linked to higher risk of heart disease, obesity, and diabetes. 4. How does late-night work affect sleep quality? It shortens total sleep time and reduces deep, restorative sleep. 5. What can reduce health risks of working late? Maintaining consistent sleep timing, limiting caffeine at night, taking breaks, and prioritising recovery on off days.