In adjusted models, adiponectin was associated with significantly higher risks of dementia and Alzheimer's disease (P=0.054 and P=0.01, respectively) in women but not in men, acceding to researcher Ernst Schaefer, MD, of Tufts University in Boston.

Some work has suggested that cardiovascular risk factors such as type 2 diabetes and high blood pressure also could be risk factors for dementia and Alzheimer's disease. Specifically with regard to type 2 diabetes, insulin resistance and inflammation may be the mechanisms underlying the association for for dementia and Alzheimer's disease, the researchers said.

Other cardiovascular risk factors, such as C-reactive protein (CRP), homocysteine, and lipoprotein-associated phospholipase (Lp-PLA2) have also been suggested as potential mediating factors in the relationship.

So to assess whether insulin signaling and inflammatory markers have any effect on the development of dementia and Alzheimer's disease, the researchers looked at data on 840 patients in the prospective Framingham Heart Study who had certain serum biomarkers measured in 1985-1988.

Specifically, they assessed levels of adiponectin, CRP, gucose, glycated albumin, insulin, and Lp-PLA2.

During a mean follow-up of 13 years, 159 patients developed dementia, including 125 with Alzheimer's disease.

After adjustment, only higher adiponectin levels in women were associated with a higher risk of dementia and Alzheimer's disease.

Also, women whose baseline adiponectin levels were higher than the median had a greater risk of dementia and Alzheimer's disease than did those whose values fell below the median at baseline.

Elevated adiponectin has been associated with impaired renal function and harmful weight loss, and dementia patients usually experience weight loss that may be linked with adiponectin levels according to the research. They noted, however, that it's well-established that insulin signaling is dysfunctional in the brains of patients with Alzheimer's disease.

"Since adiponectin enhances insulin sensitivity, one would also expect beneficial actions protecting against cognitive decline," they wrote. "Our data, however, indicate that an elevated adiponectin level was associated with an increased risk of dementia and Alzheimer's disease in women."

The researchers also noted that adiponectin levels may rise as a "protective response to vascular damage or changes in brain morphology that had not yet been identified at time of enrollment into the study."

Thus, the researchers called for further study to clarify the relationship between adiponectin levels and cognitive decline over time.

Also in the study, the researchers found that higher levels of CRP were initially associated with a lower risk of both dementia and Alzheimer's disease, but the associations lost their significance in multivariate analyses.

"We did not find indications that plasma insulin, glucose, and glycated albumin levels were associated with Alzheimer's disease or all-cause dementia," they added. "In addition, the inflammatory marker Lp-PLA2 was not associated with Alzheimer's disease or all-cause dementia."

The study was potentially limited in its generalizability because the sample was largely white, and because the lack of association between some biomarkers and risk could have been a reflection of the age at which they were tested.

Also, circulating levels may not reflect concentrations in the brain or in cerebrospinal fluid, they cautioned.

The study was supported by grants from the National Institutes of Health, Siriraj Hospital, and the U.S. Department of Agriculture.

Reference: van Himbergen TM, et al "Biomarkers for insulin resistance and inflammation and the risk for all-cause dementia and Alzheimer disease" Arch Neruol 2012; DOI: 10.1001/archneurol.2011.670.