LOS ANGELES – When Derek LeRoith, MD, PhD, was a medical student, he remembers professors telling him that human tissue response to aging diminishes over time, and that individuals can develop insulin resistance purely from aging.

Dr. Derek LeRoith, professor of medicine and director of research in the division of endocrinology at Icahn School of Medicine at Mount Sinai, New York Doug Brunk/MDedge News

Dr. Derek LeRoith

“Whether that was right or wrong I don’t know, but certainly it seems to be one of the major issues that leads to the increase in diabetes, with all of its associated aspects such as dyslipidemia and hypertension,” he said at the World Congress on Insulin Resistance, Diabetes & Cardiovascular Disease.

According to Dr. LeRoith, professor of medicine and director of research in the division of endocrinology at Icahn School of Medicine at Mount Sinai, New York, studies have demonstrated that the elderly have worse glucose tolerance, compared with younger adults. One such analysis found that the insulin secretion index and disposition index are lower in the elderly, compared with their younger patients (Diabetes 2003;52[7]:1738-48). “But it’s not just the insulin resistance per se,” he said. “It’s also a defect of the beta cell. Studies have shown that beta cell function declines with age regardless of diabetes status. This is characterized by abnormal pulsatile insulin response, decreased beta-cell responsiveness to glucose, increased proinsulin-to-insulin ratio, and decreased insulin production and secretion.”

Another major issue for aging patients is the impact of diabetes on cognitive decline and the formation of Alzheimer’s disease. “There’s a suggestion that the brain has insulin resistance and that this may also affect cognitive decline and Alzheimer’s,” Dr. LeRoith said. “But there are other aspects: insulin insufficiency, hyperglycemia, and, of course ... hypoglycemia. There is a debate as to what the major causes are. Is it amyloid beta accumulation, or is it vascular damage?”

In collaboration with Israeli researchers, Dr. LeRoith and his associates have been evaluating patients that belong to the Maccabi Health System in Tel Aviv, which has a diabetes registry with complete hemoglobin A1c measurements since 1998. One study of 897 registry participants found a strong association between worse diabetes control and worse cognition (Am J Geriatr Psych 2014;22:1055-9). Specifically, an interaction of duration of type 2 diabetes with HbA1c was associated with executive functioning (P = .006), semantic categorization (P = .019), attention/working memory (P = .011), and overall cognition (P = .006), such that the associations between duration of type 2 diabetes and cognitive impairment increased as HbA1c levels increased – but not for episodic memory (P = .984).

In a separate analysis of patients from the same registry, Dr. LeRoith and his colleagues evaluated the relationships of long-term trajectories of glycemic control with cognitive performance in cognitively normal elderly with type 2 diabetes (PLoS ONE 9[6]:e97384 doi: 10.1371/journal.pone.0097384). They found that subjects with stable HbA1c over time had the lowest HbA1c at study entry and performed best on cognitive measures, “suggesting that the trajectile of HbA1c over 10 or 12 years can really influence the cognitive ability in these patients,” he said.

Another, unrelated study found that insulin in combination with other diabetes medication is associated with less Alzheimer’s neuropathology (Neurology 2008;71:750-7), while an Alzheimer’s mouse model from Dr. LeRoith and his colleagues demonstrated that high dietary advanced glycation end products are associated with poorer spatial learning and accelerated amyloid beta deposition (Aging Cell 2016;15:309-16). “From that study we conclude that high dietary advance glycation end (AGE) products may be neurotoxic and that a diet low in AGEs may decrease dementia risk, particularly in diabetic elderly who are at increased risk and have higher levels of AGEs,” he said.

Potential ways to mitigate some of aging’s effects on the course of diabetes include caloric restriction, exercise, and taking metformin, Dr. LeRoith said. “There is a correlation between fitness and cognitive function, so the implication for clinical practice in individuals with diabetes is to encourage them to engage in physical activity on most days of the week,” he said. “It’s also known that depression makes the diabetes worse and depression makes cognitive function worse. It’s been suggested that if you have patients who are depressed, you should treat them with antidepressants if necessary, because this may help with their cognitive function.”

Meanwhile, an ongoing trial first announced in 2016 known as Targeting Aging with Metformin (TAME) is exploring the effects of metformin in helping to delay the aging process (Cell Metab 2016;23[6]:1060-5). Early support exists that metformin may delay cognitive decline and Alzheimer’s, even in non–type 2 diabetes. “An intended consequence of this effort is to create a paradigm for evaluation of pharmacologic approaches to delay aging,” the researchers wrote in an article describing the project, which is funded by the National Institute on Aging. “The randomized, controlled clinical trial we have proposed, if successful, could profoundly change the approach to aging and its diseases and affect health care delivery and costs.”

Dr. LeRoith reported having no financial disclosures.