Association of Midlife Diet With Subsequent Risk for Dementia

Importance: Observational studies suggest that diet is linked to cognitive health. However, the duration of follow-up in many studies is not sufficient to take into account the long preclinical phase of dementia, and the evidence from interventional studies is not conclusive. Objective: To examine whether midlife diet is associated with subsequent risk for dementia. Design, Setting, and Participants: Population-based cohort study established in 1985-1988 that had dietary intake assessed in 1991-1993, 1997-1999, and 2002-2004 and follow-up for incident dementia until March 31, 2017. Exposures: Food frequency questionnaire to derive the Alternate Healthy Eating Index (AHEI), an 11-component diet quality score (score range, 0-110), with higher scores indicating a healthier diet. Main Outcome and Measures: Incident dementia ascertained through linkage to electronic health records. Results: Among 8225 participants without dementia in 1991-1993 (mean age, 50.2 years SD, 6.1 years; 5686 69.1% were men), a total of 344 cases of incident dementia were recorded during a median follow-up of 24.8 years (interquartile range, 24.2-25.1 years). No significant difference in the incidence rate for dementia was observed in tertiles of AHEI exposure during 1991-1993, 1997-1999 (median follow-up, 19.1 years), and 2002-2004 (median follow-up, 13.5 years). Compared with an incidence rate for dementia of 1.76 (95% CI, 1.47-2.12) per 1000 person-years in the worst tertile of AHEI (lowest tertile of diet quality) in 1991-1993, the absolute rate difference for the intermediate tertile was 0.03 (95% CI, -0.43 to 0.49) per 1000 person-years and for the best tertile was 0.04 (95% CI, -0.42 to 0.51) per 1000 person-years. Compared with the worst AHEI tertile in 1997-1999 (incidence rate for dementia, 2.06 95% CI, 1.62 to 2.61 per 1000 person-years), the absolute rate difference for the intermediate AHEI tertile was 0.14 (95% CI, -0.58 to 0.86) per 1000 person-years and for the best AHEI tertile was 0.14 (95% CI, -0.58 to 0.85) per 1000 person-years. Compared with the worst AHEI tertile in 2002-2004 (incidence rate for dementia, 3.12 95% CI, 2.49 to 3.92 per 1000 person-years), the absolute rate difference for the intermediate AHEI tertile was -0.61 (95% CI, -1.56 to 0.33) per 1000 person-years and for the best AHEI tertile was -0.73 (95% CI, -1.67 to 0.22) per 1000 person-years. In the multivariable analysis, the adjusted hazard ratios (HRs) for dementia per 1-SD (10-point) AHEI increment were not significant as assessed in 1991-1993 (adjusted HR, 0.97 95% CI, 0.87 to 1.08), in 1997-1999 (adjusted HR, 0.97 95% CI, 0.83 to 1.12), or in 2002-2004 (adjusted HR, 0.87 95% CI, 0.75 to 1.00). Conclusions and Relevance: In this long-term prospective cohort study, diet quality assessed during midlife was not significantly associated with subsequent risk for dementia.