Plasma Growth Hormone During Sleep in Young and Aged Men

Plasma growth hormone measured at 20-min intervals across the night via indwelling venous cannula revealed a significant reduction in 16 healthy aged men as compared with 14 healthy young men. The decrease in growth hormone was entirely confined to the first 3 hours of the night (M +/- SEM for the integrated level was 5.0 +/- 1.2 and 21 +/- 4.2 ng . hr/ml). Growth hormone across the latter part of the night did not differ. Day and evening growth hormone levels measured hourly in five of the aged and nine of the young men failed to reveal an age effect. Growth hormone release is known to be associated with sleep onset, and particularly with slow wave sleep, stage 3 and 4, which was reduced in amount in these aged men (9.9 +/- 1.9 and 22.8 +/- 2.3% of time in bed for aged and young groups, respectively). Sleep stage 3 and 4 correlated significantly with growth hormone level (R = .463, p less than .01) for young and aged men combined, but not for either age group alone, indicating that growth hormone does not have a direct, simple relationship with slow wave sleep.