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AlzRisk Paper Detail

Reference: Muller, 2007
Cohort: Washington Heights-Inwood Columbia Aging Project
Risk Factor: Diabetes Mellitus

Average Follow-up Time Detail
This analysis was based on a subset of participants in the initial WHICAP cohort who had their insulin levels measured at baseline between 1992 and 1994. 997 participants had their insulin levels measured; however, only 542 were included in the analysis.

Average follow-up time was not reported for this subset of 542 participants.

Exposure Detail
Insulin levels (measured in μIU/mL) were obtained at baseline from serum collected after a night of fasting, in a subset of participants from the first wave of the study. In this analysis, the authors categorized participants according to whether they had insulin levels above the 75th percentile or not, following the European Group for Study of Insulin Resistance (EGIR) definition of insulin resistance. The actual fasting insulin value corresponding to this 75th percentile cut-point in this sample was not reported.

More details on the EGIR are available in Grundy SM, Cleeman JL, Daniels SR, et al., Circulation 2005; 112, 2735-2752.

"Fasting insulin levels were conducted in a sample of the study population from cohort 1 (N=997)[19] and were measured in μIU/mL from serum collected at baseline under overnight fasting conditions and frozen at −70 °C. Insulin levels were measured using a solid-phase chemiluminescent enzyme immunoassay (Immulite, Diagnostic Products, Los Angeles, CA)."

Ethnicity Detail
Members of the cohort were grouped into one of three ethnicity groups: African-American, Caucasian and Hispanic. However, the race distribution of participants in the subset with available insulin values on which this analysis is based has not been reported.

Screening and Diagnosis Detail
AD Diagnosis:
DSM IV Diagnostic and Statistical Manual IV
NINCDS ADRDA National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association Criteria (McKhann 1984)

Total dementia definition:
DSM-IV criteria and evidence of: cognitive deficit on neuropsychological testing and social or occupational function impairment (CDR > 1).

"Dementia diagnosis and specific cause assignment was made by consensus of two neurologists, one psychiatrist, and two neuropsychologists based on baseline and follow-up information that included the neuropsychological history, medical history, assessment of function, and neurological examination5,6,21. Brain imaging was not used for dementia diagnosis. Dementia diagnosis was based on Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV criteria and required evidence of cognitive deficit on neuropsychological testing and evidence of social or occupational function impairment (CDR > 1)25, AD diagnosis was based on NINCDS-ADRDA criteria26. A diagnosis of probable AD was made when dementia could not be explained by other disorders. A diagnosis of possible AD was made when the most likely cause of dementia was AD, but there were other disorders that could contribute such as stroke."

Covariates & Analysis Detail
Analysis Type:
Cox proportional hazards regression

"The time-to-event variable was the age at dementia onset, to interpret the hazard function as the age-specific incidence of the disease. Secondary analyses were done with follow-up as the time-to-event variable. Individuals who did not develop the outcome of interest, died, or were lost to follow-up were censored at the time of their last evaluation. Individuals with dementia not caused by the subtype of interest were censored at the time of dementia onset."

AD Covariates:
APOE4APOE e4 genotype
SMsmoking status

TD Covariates:
APOE4APOE e4 genotype
SMsmoking status