It has been estimated that most people lose between 35% and 45% of skeletal muscle in the 6 decades between the ages of 20 and 80. This progressive loss of muscle is known as sarcopenia and, combined with osteoporosis, is responsible for the loss of strength, increasing frailty, and loss of independence seen in many elderly people.
Along with lack of regular exercise, declining levels of growth hormone are thought to be linked to muscle loss. A new study published in Annals of Internal Medicine describes the effect of the orally active ghrelin agonist, MK-677, in healthy adults aged 60-81 years.
Daily dosing with 25mg MK-677 was generally well tolerated and increased levels of growth hormone and insulin-like growth factor-1 to those of healthy young adults. Over 1 year, mean fat-free mass declined in the placebo group, but increased by 20% in the MK-677 treated group. MK-677 induced a transient increase in appetite; body weight increased by 2.7 kg in the MK-677 treated group, but by only 0.8 kg in the placebo treated group. Overall, treatment with MK-677 had a positive effect on three factors that contribute to loss of muscle mass: reduced growth hormone levels, loss of fat-free mass, and inadequate food intake. The increase in lean mass seen with MK-677 therapy did not translate into enhanced strength or function, but the researchers say that “the study sets the stage for an adequately powered clinical trial of sufficient duration in a population vulnerable to frailty”.