Mounting evidence indicates that blood sugar and insulin have profound effects on cognitive function. Many patients—and medical professionals, themselves—are only too familiar with the brain fog and difficulty focusing that often accompany hypo- and hyperglycemia. But that’s in the acute sense. What about the long term, over the course of a lifetime? A growing body of research suggests that keeping blood glucose and insulin within a healthy range is good for more than warding off metabolic syndrome; it may be important for staying sharp in older age.

It has long been known that type 2 diabetes (T2D) is associated with increased risk for Alzheimer’s disease. In fact, Alzheimer’s is frequently referred to as “type 3 diabetes,” owing to problems with impaired glucose metabolism and insulin signaling in the brain. Even blood glucose that’s not in the diabetic range, but is higher than normal, has been shown to be associated with increased risk for dementia. So it’s not only those with T2D who should be concerned about their cognitive future; it’s everyone.

And what about people with type 1 diabetes? The etiology of type 1 (T1D) is completely different from that of type 2, but owing to large fluctuations in blood glucose and long term insulin therapy, the long term complications of T1D are nearly the same: retinopathy, nephropathy, cardiovascular disease, and in some cases, even weight gain or obesity and other signs of metabolic syndrome. Individuals with T1D who rely on large boluses of insulin to cover a high carbohydrate intake may eventually develop metabolic syndrome, which is basically “insulin resistance syndrome.” This unfortunate state is called “double diabetes.” (New research supports the use of low-carbohydrate diets to reduce the insulin doses those with T1D need. They will always require at least some exogenous insulin, but a low carbohydrate intake may allow them to use much less than when following a high-carb diet, and the lower doses may result in fewer bouts of hypo- and hyperglycemia.)         

According to research from the Joslin Diabetes Center in Boston, people who’ve lived with T1D for decades—at least 50 years, in this study—have a very mild decrease in cognitive performance and this was also correlated with cardiovascular disease. Taking into account what research has uncovered about long term chronic hyperinsulinemia and increased risk for cardiovascular disease, it stands to reason that individuals with T1D who have used insulin—particularly relatively high amounts of insulin—for a few decades may be at increased risk for cardiovascular disease, and chronically high insulin (and perhaps administration of large insulin doses) is also a driving risk factor in Alzheimer’s disease and memory decline.  

The Joslin study isn’t necessarily cause for alarm. The decline in cognitive performance wasn’t negligible, but it was very small. According to one of the researchers, “Overall, nobody among the Medalists needs to worry; this is a very healthy group that’s showing minimal signs of cognitive decline. However, these small deficits may be avoidable with self-care behaviors that help minimize diabetes complications.” (“Medalists” refers to Joslin 50-year Medalists, who are people who’ve lived with T1D for at least that long.)

Such self-care behaviors could presumably include anything that maintains or increases insulin sensitivity, as well as possibly adopting a low-carbohydrate diet to make blood glucose excursions much smaller than they typically are on a standard modern Western diet, which, for many people, will lead to reductions in mealtime insulin doses. If chronically high insulin, or insulin resistance induced by long-term insulin therapy, increase risk for declining cognition—however mildly—patients should take “the long view” and gain an appreciation for healthy glucose and insulin levels as protective not only for the body, but also the brain.  

By Amy Berger, MS, CNS