We read with great interest the article by Baker and colleagues1 showing that 20 weeks of subcutaneous growth hormone–releasing hormone (GHRH) administration had favorable effects on cognition in both adults with mild cognitive impairment and healthy older adults. These findings highlight the therapeutic potential of administering GHRH to slow the rate of age-related cognitive decline. However, the mechanism through which GHRH improved cognitive functions in this cohort requires more detailed discussion. During aging, there is a pronounced decline in the total amount of slow-wave sleep (SWS), which coincides with reduced activity of the somatotropic axis.2 This is a likely contributor to age-related memory deficits, as SWS is critical for the formation of long-term memories.3 It has also been demonstrated that pharmacologic increases in SWS preserve sustained attention and reaction time in humans, implicating it in cognitive functioning more broadly.4 These findings suggest that sleep loss, especially SWS loss, may contribute to age-related cognitive decline. As exogenous GHRH is known to stimulate sleep (especially SWS5), it seems plausible that the favorable effects on cognition in response to GHRH observed by Baker and colleagues stemmed from improved sleep architecture. Using the Pittsburgh Sleep Quality Index,6 which is a comprehensive self-report measure of sleep quality and impairment, the authors did not find improvements in self-reported sleep quality in response to their intervention. However, as no objective measure of sleep was administered (eg, polysomnography), it cannot be ruled out that the beneficial effects of GHRH on cognitive functions in cognitively healthy and cognitively impaired older subjects were mediated by changes in sleep architecture.
Benedict C, Chapman CD, Schiöth HB. Growth Hormone–Releasing Hormone Improves Cognitive Function in Older Adults: Sleep On It. JAMA Neurol. 2013;70(4):529–530. doi:10.1001/2013.jamaneurol.349
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