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Dietary intake of vitamin C was evaluated using the CHAP food frequency questionnaire (FFQ), which was administered a mean of 1.7 years after baseline (about 2.3 years before the first follow-up visit). The questionnaire addressed food consumption during the past year. Nutrient intakes were adjusted for total energy intake using the regression residual method (Willett W, Stampfer MJ. Total energy intake: implications for epidemiologic analyses. Am J Epidemiol 1986; 124:17-27), and it was these calorie-adjusted intakes that were used in the analyses of vitamin C and AD.
"Study participants completed a self-administered food frequency questionnaire... The CHAP food frequency questionnaire, a modified version of the Harvard food frequency questionnaire, (31, 32) was used to measure usual intake of 139 food items throughout the previous year, as well as the use of vitamin supplements. Nutrient intakes were computed by multiplying the nutrient contents of food items by frequency of consumption and summing across all items. Nutrient levels were adjusted for total energy intake separately for men and women by using the regression residual method (33)."
Age at start of follow-up is the age at enrollment. Vitamin C intake was assessed on average 1.7 years later, which was on average 2.3 years prior to dementia assessment.
Screening and Diagnosis Detail
National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association Criteria (McKhann 1984)
Other diagnostic criterion:
Although investigators used the NINCDS-ADRDA criteria as the basis for identifying AD cases, they also identified cases as "persons who met the criteria but had another coexisting condition that was thought to contribute to dementia."
“The 2 1⁄2-hour clinical evaluations were conducted in participants’ homes by a team consisting of a neurologist, nurse practitioner, and neuropsychological technician. The evaluations included a medical history, a structured neurological examination, neuropsychological testing (using the tests of Consortium Established for Research on Alzheimer’s Disease, CERAD
), informant interviews, and laboratory testing. Magnetic resonance imaging (MRI) was performed when dementia was evident and stroke occurrence was clinically uncertain (9 persons). A board-certified neurologist blinded to the dietary assessment data reviewed all clinical evaluation data before making clinical diagnoses of neurological diseases. Diagnoses of AD were made according to criteria of the National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer’s Disease and Related Dementia Association (NINCDS ADRDA),
except that we did not exclude as cases persons who met the criteria but had another coexisting condition that was thought to contribute to dementia. Eleven persons with incident dementia caused by a condition other than AD were analyzed as noncases.”
Covariates & Analysis Detail
Sample design accounted for use of weights in the analysis
Total caloric intake was adjusted for using the regression residual method (Willett W, Stampfer MJ. Total energy intake: implications for epidemiologic analyses. Am J Epidemiol 1986; 124:17-27).
APOE e4 genotype
follow up time
Analysis included an interaction term between race and APOE e4.
Nutrient intakes were adjusted for total energy intake using the regression residual method.