Sleep loss is associated with insulin resistance and an increased risk for type 2 diabetes, yet underlying mechanisms are not understood. Elevation of circulating non-esterified (i.e. free) fatty acid (NEFA) concentrations can lead to insulin resistance and plays a central role in the development of metabolic diseases. Circulating NEFA in healthy individuals shows a marked diurnal variation with maximum levels occurring at night, yet the impact of sleep loss on NEFA levels across the 24 h cycle remains unknown. We hypothesised that sleep restriction would alter hormones that are known to stimulate lipolysis and lead to an increase in NEFA levels.

We studied 19 healthy young men under controlled laboratory conditions with four consecutive nights of 8.5 h in bed (normal sleep) and 4.5 h in bed (sleep restriction) in randomised order. The 24 h blood profiles of NEFA, growth hormone (GH), noradrenaline (norepinephrine), cortisol, glucose and insulin were simultaneously assessed. Insulin sensitivity was estimated by a frequently sampled intravenous glucose tolerance test.

Sleep restriction relative to normal sleep resulted in increased NEFA levels during the nocturnal and early-morning hours. The elevation in NEFA was related to prolonged nocturnal GH secretion and higher early-morning noradrenaline levels. Insulin sensitivity was decreased after sleep restriction and the reduction in insulin sensitivity was correlated with the increase in nocturnal NEFA levels.

Sleep restriction in healthy men results in increased nocturnal and early-morning NEFA levels, which may partly contribute to insulin resistance and the elevated diabetes risk associated with sleep loss.