The Diabetes-Alzheimer's Connection

Alzheimer's disease is a chronic and incurable neurological disorder responsible for most cases of dementia. Eventually it progresses to personality changes, deterioration of intellectual function, problems with speech and language, coma, and death. The Alzheimer’s Association estimates that more than 5 million people in the United States have the disease and the prevalence is expected to triple over
the next 40 years.

Diabetes, a disorder characterized by high levels of blood sugar, increases the risk of developing Alzheimer's disease. When blood
sugar levels are high, excessive amounts of advanced glycosylation
end products (AGEs) and free radicals are formed. Free radicals are unstable molecules missing an electron and they readily react with other molecules in order to gain one, causing a chain reaction that triggers inflammation and cell damage. Free radicals and inflammation can also cause injury to the lining of blood vessels, initiating atherosclerosis and increasing the risk for stroke (death of brain tissue).

Alzheimer’s disease is characterized by the presence of amyloid plaques and neurofibrillary tangles in the brain. Plaques are made up of dead and damaged cells and protein deposits which become bunched and tangled together. AGEs have been found in these plaques and tangles.

A study published last year in the journal Neurology followed 135 people for 10 to 15 years, measuring levels of blood glucose and insulin, testing for insulin resistance, and monitoring for symptoms of Alzheimer’s disease. After participants died, the researchers examined their brains. They found that high levels of blood sugar and insulin were associated with an increased risk for developing Alzheimer’s disease, independent of age, sex, body-mass index, smoking, exercise, blood pressure, cholesterol, and cerebrovascular disease. People with the highest levels of insulin had six times the risk of developing brain plaques compared to those with the lowest levels.

In a study published in Lancet Neurology, researchers at the University of California, San Francisco found that up to half of all cases of Alzheimer’s disease could be prevented through modifiable risk factors. These include stopping smoking, being physically active, and treating other chronic illnesses including obesity, high blood pressure, and diabetes.

References:

Alzheimer’s Association, 2010 Alzheimer’s Disease Facts and Figures, Alzheimer’s & Dementia, Volume 6.

Barnes DE and Yaffe K. 2011. The projected effect of risk factor reduction on Alzheimer's disease prevalence. Lancet Neurology 10(9):819-28.

Matsuzaki, T et al. 2010. Insulin resistance is associated with the pathology of Alzheimer disease. The Hisayama Study. Neurology 75(9):764-70.