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A growing body of scientific evidence links cardiovascular risk factors and diabetes to Alzheimer's disease and other forms of mental deterioration.
"Brain metabolism and brain pathology are intimately related with the pathology of other parts of the body," says Hugh Hendrie, MB, ChB, DSc, of the Indiana University Center for Aging Research in Bloomington, Ind.
"The accumulation [of data] has been a consistent story," Hendrie says. "People are targeting this particular constellation of risk factors and coming up with answers and seeing that the connections are, in fact, quite valid. For instance, cholesterol levels, hypertension, and now with diabetes."
One part of this relationship is the link between cholesterol and Alzheimer's disease.
An analysis of data from the Harvard Women's Health study, presented at the recent 9th International Conference on Alzheimer's Disease and Related Disorders in Philadelphia, focused on cholesterol and mental function in aging women. The study found significantly greater cognitive performance with both higher HDL levels and lower LDL levels. The risk of cognitive impairment decreased with increasing HDL cholesterol and increased with increasing LDL cholesterol.
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The correlation was strongest between cognitive function and HDL, according to principal investigator Elizabeth Devore, a doctoral candidate at Harvard School of Public Health in Boston.
"HDL levels were essentially driving our results, which is not to say that LDL levels are not important to keep in check but just that HDL levels are the most predictive factor [of Alzheimer's disease]," Devore says.
Some research suggests that statin therapy may reduce the risk of developing Alzheimer's disease. An animal study reported at the Alzheimer's conference by researchers at University of Alabama, Birmingham, showed that mice treated with simvastatin (Zocor, Merck) were better able to remember their way through a maze than untreated animals.
In 2002, Boston University neurologist and epidemiologist Robert C. Green, MD, reported that a study of 2,581 people followed for more than 6 years at 15 medical centers revealed that taking statins was associated with a 79% reduction in the risk of developing Alzheimer's disease.1
Although preliminary data suggest that statins may offer a protective effect against the development of Alzheimer's disease, there is not yet enough to support wider use of the drugs, according to Lisa Miller, PharmD, BCPP, CGP, of Memorial Hermann Southwest Hospital in Houston, Tex.
COGNITION AND GLYCEMIC CONTROL
Another important part of this interrelationship is the correlation of cognitive decline with poor glucose control.
"If you chronically expose the brain to high levels of blood sugar, it becomes insensitive or inefficient," says neurologist William Rodman Shankle, MD, of University of California, Irvine. "In addition to the changes that occur in the blood vessel walls, which become hard and brittle, the ability of the brain to function efficiently starts to decline with chronically elevated blood sugar."
One recent study, reported in the June 2004 issue of the Archives of Internal Medicine, concluded that elderly white women with diabetes had a more rapid cognitive decline than those without diabetes.2 In the March 2004 issue of the British Medical Journal, another study in women showed that mental function was worse the longer the patient had had diabetes.3
The good news is that the latter study also showed that diabetes treatment could have a positive effect on mental decline.
Of the 1,248 women with type 2 diabetes who participated in the study, those taking oral hypoglycemic agents performed as well as women without diabetes. Women with type 2 diabetes who did not report taking pharmaceutical treatment performed significantly worse than the others.3
Hendrie notes that it makes sense for diabetes treatment to have a protective effect against the deterioration of mental function, and he suggests adding studies of cognition to studies of patients with type 2 diabetes.
"We know already that treatments of diabetes affect organs like the
kidneys and eyes, and so now we should be aware of how treatment of diabetes
could well affect what is happening in the brain," Hendrie says.
"It is hopeful because we know something about being able to prevent
hypertension and more about how to prevent diabetes, so it's reassuring that
those interventions might also help to preserve the brain." 
References
2. Kanaya AM, Barrett-Connor E, Gildengorin G, Yaffe K: Change in
cognitive function by glucose tolerance status in older adults: a 4-year
prospective study of the Rancho Bernardo study cohort. Arch Intern
Med 164:1327–1333, 2004.
3. Logroscino G, Kang JH, Grodstein F: Prospective study of type 2
diabetes and cognitive decline in women aged 70–81 years.
BMJ 328:548, 2004.
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