Diabetes, Exercise and Memory

Bruce S. McEwen, Ph.D.

There is a rising tide of obesity and diabetes in the US and throughout the world. In the US alone, there are estimated to be ~ 20 million affected individuals. The incidence of type 2 Diabetes Mellitus rose 41% between 1997 and 2003 and 60% of new cases are obese while among children > 90% of new cases are obese. While most of us think of diabetes and obesity as primarily a body problem, a new research paper highlights the influence of glucose control on memory and the architecture of a brain region called the hippocampus, which is essential for our ability to remember daily events and spatial information. In Type 2 diabetics, the volume of the hippocampus, determined by non-invasive brain imaging, was smaller in relation to the degree of elevated glucose in the blood and along with that there was also impairment of memory functions that depend on the hippocampus. Moreover, there is evidence that Type 2 diabetes and poor glucose control increase the risk of developing dementia later in life.

How do the effects of poor glucose control on the hippocampus come about? The hippocampus needs glucose to function properly and the body actually mobilizes and increases glucose levels when we are challenged to use our brains. Lack of adequate glucose in the hippocampus is why it is sometimes good to eat a candy bar before taking a test. And the hippocampus has receptors for insulin, a key hormone that controls glucose levels. A recent study shows that, in hippocampus of rats with experimental diabetes, the ability of glucose to be transported into brain cells is impaired by alterations in the cellular signaling pathway by which the molecules that transport glucose into cells are first placed in the cell membrane and then activated to do their transporting. These mechanisms are very similar to the mechanisms for glucose transport that exist in muscle.

Although managing obesity and diabetes in society is a huge and complex problem, there are some things that individuals can do to reduce the chances of developing Type 2 diabetes. Previous work has highlighted how regular exercise prevents diabetes and improves cognitive function. In these studies, it was not necessary to become a marathon runner Ð rather, for sedentary adults, walking 30 minutes a day was effective providing it was sustained over a 6 year period. Interestingly, only a 6 month intervention was effective in inducing better attention and decision making and in changing activation patterns in the brain, as assessed by brain scans.

But maintaining habits of daily, regular exercise over months and years requires social interactions Ð support groups, friends who get people out the door when they are not feeling quite in the mood to do their daily walk. Exercise of this kind is often a social enterprise and social support is known to have broad benefits upon health. For example, having more than 3 regular social contacts has been shown to reduce the cumulative burden of chronic stress in both men and women. Thus, what common sense has told us is now supported by a deepening understanding of the underlying biology, because we now recognize specific mechanisms and processes by which physical activity and social relationships benefit brain and body health. And, as we have noted above, these include the prevention of diabetes and the enhancement of brain function.

References:

Gold SM, Dziobek I, Sweat V, Tirsi A, Rogers K, Bruehl H, Tsui W, Richardson S, Javier E, Convit A (2007) Hippocampal damage and memory impairments as possible early brain complications of type 2 diabetes. Diabetologia 50:711-719.

Gold PE (1987) Sweet Memories. American Scientist 75:151-155.

Piroli GG, Grillo CA, Reznikov LR, Adams S, McEwen BS, Charron MJ, Reagan LP (2007) Corticosterone impairs insulin-stimulated translocation of GLUT4 in the rat hippocampus. Neuroendocrinology 85:71-80.

Kramer AF, Hahn S, Cohen NJ, Banich MT, McAuley E, Harrison CR, Chason J, Vakil E, Bardell L, Boileau RA, Colcombe A (1999) Ageing, fitness and neurocognitive function. Nature 400:418-419.

Colcombe SJ, Kramer AF, Erickson KI, Scalf P, McAuley E, Cohen NJ, Webb A, Jerome GJ, Marquez DX, Elavsky S (2004) Cardiovascular fitness, cortical plasticity, and aging. Proc. Natl. Acad. Sci. USA 101:3316-3321.

Seeman TE, Singer BH, Ryff CD, Dienberg G, Levy-Storms L (2002) Social relationships, gender, and allostatic load across two age cohorts. Psychosom. Med. 64:395-406.