A study by researchers at Columbia University's Vagelos School of Medicine has found that even mild, chronic sleep deprivation can lead to weight gain, a condition thought to affect around 30 per cent of adults. This challenges the assumption, based largely on studies of severe sleep restriction, that only extreme sleep loss affects weight, and suggests that everyday habits such as staying up slightly later than usual could carry measurable long-term health consequences.

Researchers studied 95 adults who normally slept at least seven hours a night and had existing cardiovascular and metabolic risk factors, asking them to delay their bedtime by 90 minutes for six weeks before comparing this with six weeks of normal sleep. When sleep was cut by roughly 80 minutes a night, participants gained around 0.45 kilograms (about a pound) on average and spent up to 30 minutes more time sitting each day, despite being awake longer. Notably, levels of leptin, a hormone that suppresses appetite, actually rose during sleep restriction, undermining theories that hormonal disruption drives overeating. Related studies on the same participants also linked mild sleep loss to increased insulin resistance, particularly in postmenopausal women, and to greater inflammation-related immune cell activity.