Blood Glucose and the Brain: Sugar and Short-Term Memoryby Jennifer Gibson, PharmD | June 26, 2008
Millions of older adults suffer from significant memory loss, despite the lack of a diagnosis of dementia-causing disease. This memory loss can lead to a significant decline in quality of life and often remains undiagnosed and untreated. Recently, however, scientists have begun to study the role of glucose regulation in cognitive enhancement of adults. Cognitive function and short-term memory retrieval in middle-aged and older adults may now be linked to blood sugar levels.
The brain’s primary source of fuel is glucose, unlike other organs that have multiple fuel sources. Research has long shown that ingesting drinks or foods with high glucose content before high-demand short-term memory tasks improves cognitive performance. However, people with better blood-sugar regulation performed better on the tests than those with poor glucose regulation. In other words, the faster people metabolized blood sugar, the better their memory functioned.
Moderate increases in blood glucose are effective in enhancing short-term memory performance and cognitive functioning across an array of domains, but while a little glucose is good, too much can be bad. Sustained elevations in blood sugar levels, as seen in conditions including impaired glucose tolerance and diabetes, lead to a decline in cognitive functioning. Simply, the longer that the glucose remains in the blood, the less fuel the brain has to function and retain memories.
These findings are owed, at least in part, to the fact that glucose affects the hippocampus — the part of the brain responsible for short-term memory. In one small study, people with high blood sugar levels actually had a smaller hippocampus than those with normal glucose regulation. Any type of insult or injury to the brain, including high blood sugar, easily damages the hippocampus. Fortunately, it is also a resilient part of the brain and its function can be recovered when blood sugar levels are controlled.
Recently, elevated blood sugar levels were found to be significant predictors of poor cognitive performance or mild cognitive impairment among middle-aged and elderly subjects. Adults with higher fasting blood sugar levels performed worse on memory function tests, whether they received glucose or a placebo prior to the test. These findings are also linked to lifestyle factors. Study participants that had poor glucose regulation, leading to high blood sugar levels, had more risk factors for poor overall health, diet, and lifestyle. People with known risk factors for diabetes or impaired glucose tolerance are at risk for elevated blood sugar levels, in addition to any person who is overweight or has a sedentary lifestyle.
The research requires more investigation before glucose-regulation becomes a mainstay of memory loss treatments, but it provides more incentive for adults to maintain healthy blood sugar levels. Not only does a healthy, active lifestyle prevent heart disease, diabetes, joint ailments, and a plethora of other conditions, but it also improves memory and cognitive functioning.
Roozendaal, B. (2003). The hippocampus mediates glucocorticoid-induced impairment of spatial memory retrieval: Dependence on the basolateral amygdala. Proceedings of the National Academy of Sciences, 100(3), 1328-1333. DOI: 10.1073/pnas.0337480100
Meikle, A., Riby, L.M., Stollery, B. (2004). The impact of glucose ingestion and gluco-regulatory control on cognitive performance: a comparison of younger and middle aged adults. Human Psychopharmacology: Clinical and Experimental, 19(8), 523-535. DOI: 10.1002/hup.643
Riby, L.M., McLaughlin, J., Riby, D.M. (2008). Lifestyle, glucose regulation and the cognitive effects of glucose load in middle-aged adults. British Journal of Nutrition DOI: 10.1017/S0007114508971324
Riby, L.M., Marriott, A., Bullock, R., Hancock, J., Smallwood, J., McLaughlin, J. (2008). The effects of glucose ingestion and glucose regulation on memory performance in older adults with mild cognitive impairment. European Journal of Clinical Nutrition DOI: 10.1038/sj.ejcn.1602981
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