OBJECTIVE: This study examined the association of plasma DHA, dietary DHA, and fish intake with dementia and Alzheimer's Disease (AD) in older adults.

DESIGN: Case-cohort study.

SETTING: Clinic visit in 1991-93.

PARTICIPANTS: 266 community dwelling men and women aged 67-100 years (mean=80.2).

MEASUREMENTS: Participants had neurological and neuropsychological evaluations for dementia in 1991-93. Plasma DHA was measured in blood samples obtained at that visit. Dietary intakes of DHA and fish were obtained from an earlier (1988-91) visit. Three DHA exposure variables were used in separate analyses; plasma DHA, dietary DHA, and consumption of cold-water fish. All-cause dementia included AD and other types of possible or probable dementia.

RESULTS: Among these 266 participants, 42 had dementia and 30 had possible or probable AD. Plasma DHA in the highest tertile was associated with a 65% reduced odds of all-cause dementia (95% CI: 0.17, 0.92) and a 60% reduced odds of AD (95% CI: 0.15, 1.10). Dietary DHA in the highest tertile was associated with a 73% reduced odds of all-cause dementia (95% CI: 0.09, 0.79) and a 72% reduced odds of AD (95% CI: 0.09, 0.93). Fish intake had similar, though not significant, reduced odds of dementia (OR = 0.51; 95% CI: 0.20, 1.32) and AD (OR = 0.55; 95% CI: 0.20, 1.48).

CONCLUSIONS: Plasma and dietary DHA appear to protect against dementia. Increasing DHA intake from marine sources may be recommended for reducing dementia risk.