OBJECTIVE:
To investigate the association of midlife dietary fat intake to cognitive performance, and to the occurrence of clinical mild cognitiveimpairment (MCI) later in life in a non-demented population.

DESIGN:
A longitudinal population-based study.

SETTING:
Populations of Kuopio and Joensuu, Eastern Finland.

PARTICIPANTS AND METHODS:
Participants of the CAIDE study were derived from random, population-based samples studied at midlife (1972, 1977, 1982 or 1987). After an average follow-up of 21 years, a total of 1449 (72%) individuals aged 65-80 years participated in the re-examination in 1998. Altogether 82 (5.7%) people were diagnosed as having MCI. Dietary information was collected with a structured questionnaire and an interview at midlife.

MAIN OUTCOME MEASURES:
MCI, global cognitive and executive functions, episodic, semantic and prospective memory and psychomotor speed.

RESULTS:
Abundant saturated fat (SFA) intake from milk products and spreads at midlife was associated with poorer global cognitive function and prospective memory and with an increased risk of MCI (OR 2.36, 95% CI 1.17-4.74) after adjusting for demographic and vascular factors, other fats and ApoE. On the contrary, high intake of polyunsaturated fatty acids (PUFA) was associated with better semantic memory. Also frequent fish consumption was associated with better global cognitive function and semantic memory. Further, higher PUFA-SFA ratio was associated with better psychomotor speed and executive function.

CONCLUSIONS:
Our data suggests that dietary fat intake at midlife affects cognitive performance and occurrence of MCI later in life. The impact of dietary interventions needs to be tested in clinical trials.