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A growing body of scientific evidence links cardiovascular risk factors anddiabetes to Alzheimer's disease and other forms of mental deterioration.
"Brain metabolism and brain pathology are intimately related with thepathology 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 ofrisk factors and coming up with answers and seeing that the connections are,in fact, quite valid. For instance, cholesterol levels, hypertension, and nowwith diabetes."
One part of this relationship is the link between cholesterol andAlzheimer's disease.
An analysis of data from the Harvard Women's Health study, presented at therecent 9th International Conference on Alzheimer's Disease and RelatedDisorders in Philadelphia, focused on cholesterol and mental function in agingwomen. The study found significantly greater cognitive performance with bothhigher HDL levels and lower LDL levels. The risk of cognitive impairmentdecreased with increasing HDL cholesterol and increased with increasing LDLcholesterol.
The correlation was strongest between cognitive function and HDL, accordingto principal investigator Elizabeth Devore, a doctoral candidate at HarvardSchool of Public Health in Boston.
"HDL levels were essentially driving our results, which is not to saythat LDL levels are not important to keep in check but just that HDL levelsare the most predictive factor [of Alzheimer's disease]," Devoresays.
Some research suggests that statin therapy may reduce the risk ofdeveloping Alzheimer's disease. An animal study reported at the Alzheimer'sconference by researchers at University of Alabama, Birmingham, showed thatmice treated with simvastatin (Zocor, Merck) were better able to remembertheir 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 15medical centers revealed that taking statins was associated with a 79%reduction in the risk of developing Alzheimer'sdisease.1
Although preliminary data suggest that statins may offer a protectiveeffect against the development of Alzheimer's disease, there is not yet enoughto 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 ofcognitive 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 RodmanShankle, MD, of University of California, Irvine. "In addition to thechanges that occur in the blood vessel walls, which become hard and brittle,the ability of the brain to function efficiently starts to decline withchronically elevated blood sugar."
One recent study, reported in the June 2004 issue of the Archives ofInternal Medicine, concluded that elderly white women with diabetes had amore rapid cognitive decline than those withoutdiabetes.2 In theMarch 2004 issue of the British Medical Journal, another study inwomen showed that mental function was worse the longer the patient had haddiabetes.3
The good news is that the latter study also showed that diabetes treatmentcould 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 withoutdiabetes. Women with type 2 diabetes who did not report taking pharmaceuticaltreatment performed significantly worse than theothers.3
Hendrie notes that it makes sense for diabetes treatment to have aprotective effect against the deterioration of mental function, and hesuggests adding studies of cognition to studies of patients with type 2diabetes.
"We know already that treatments of diabetes affect organs like thekidneys and eyes, and so now we should be aware of how treatment of diabetescould well affect what is happening in the brain," Hendrie says."It is hopeful because we know something about being able to preventhypertension and more about how to prevent diabetes, so it's reassuring thatthose interventions might also help to preserve the brain." 
References
2. Kanaya AM, Barrett-Connor E, Gildengorin G, Yaffe K: Change incognitive function by glucose tolerance status in older adults: a 4-yearprospective study of the Rancho Bernardo study cohort. Arch InternMed 164:1327–1333, 2004.
3. Logroscino G, Kang JH, Grodstein F: Prospective study of type 2diabetes and cognitive decline in women aged 70–81 years.BMJ 328:548, 2004.
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