Leptin is increased in OSA, even when obesity is taken into account . This suggests that OSA leads to leptin resistance. The increase in leptin in OSA may be due to increased sympathetic activity. Leptin reduces food intake, increases activity and energy expenditure and is also a respiratory stimulant, increasing the ventilatory response to carbon dioxide.
The increase in sympathetic activity probably increases the energy expenditure despite the reduction in physical activity that is seen in OSA during the day. At night there is increased energy expenditure due to the high work of breathing and frequent arousals, and the movements that these cause.
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