Sarcopenia and cognitive ageing: investigating their interrelationship, biological correlates and the role of glucocorticoids
Kilgour, Alexandra Helen Middleton
Background Sarcopenia and age-related cognitive decline (ARCD) are important age-related conditions which significantly impact upon the quality of life of older adults. ARCD is a well-established research area, whereas sarcopenia is a relatively new field. Research into the inter-relationships between them and possible common underlying mechanistic processes is lacking. Methods Several research techniques were used: a large systematic review; the development of an image analysis technique to measure neck muscle size on volumetric MR brain scans; the subsequent use of the technique in elderly cohort studies; statistical modelling to investigate the role of glucocorticoids in sarcopenia; and an invasive clinical study to develop a novel technique to measure the activity of 11beta-hydroxysteroid dehydrogenase (11βHSD1) in the human brain in vivo. Results I consistently found a relationship between: some measures of brain structure and muscle size; markers of brain structure and muscle function, mostly grip strength and gait speed; and cognition and muscle function. However, I found no relationship between current cognition and muscle size in any of the above studies. Cortisol was identified as a possible explanatory factor in the relationship between both cognition and brain volume with gait speed. I found an association between markers of immunosenescence and sarcopenia (neck muscle CSA and grip strength) and an association between expression of the cortisol amplifying enzyme 11βHSD1 and quadriceps strength. I developed a technique to measure 11βHSD1 activity across the human brain, which found that the amount of cortisol produced within the brain was not detectable and highlighted the asymmetries within the cerebrovascular venous system. Conclusions Further longitudinal studies looking at the association between sarcopenia and ARCD are now required to investigate these important relationships further and hopefully this will lead to improved therapeutic options.