MODULE SUPPLEMENT: ENDOCRINE SYSTEM
What Causes These Changes?

Few morphologic changes are reported to occur in the endocrine pancreas, although there may be some atrophy, as is common to most organ systems. In terms of the various hormones produced, somatostatin levels are noted to increase with age as they do in the brain. This can inhibit insulin secretion in response to glucose. At the same time, data are conflicting about whether insulin secretion is maintained or less efficient. Elahi & Muller (2000) report data suggesting that in healthy older adults without diabetes, neither first nor second phase insulin response differs significantly from those of younger adults. In contrast, others suggest that with aging maximal stimulated insulin secretion is reduced (Ratnakant, Ochs, & Solomon, 2003). This may suggest that healthy older adults can function well under normal circumstances but have less reserve to meet glucose challenges.

What about the peripheral response to insulin? In general, most data suggest that there is increased resistance to the glucose disposing actions of insulin with age (Elahi & Muller, 2000; Timiras, 2003). This appears to be especially related to changes in fat mass, which tends to increase with age, fat distribution, which tends to be more centrally located in older adults, and physical fitness, since many older adults become less active with age. Insulin suppression of hepatic glucose production, however, appears to remain intact (Elahi & Muller, 2000), although not all agree (Timiras, 2003).