Association of Midlife Diet With Subsequent Risk for Dementia

Abstract

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.

Figure 1.. Flowchart of Sample Selection for Whitehall II Study

The end of follow-up for dementia occurred on March 31, 2017. There was continuous linkage for dementia ascertainment throughout all of the years of follow-up. ^aAt each wave of data collection, individuals participated in at least 1 part of the clinical examination (providing data from the food frequency questionnaire [1991-1993, 1997-1999, 2002-2004], from the cognitive examination [1997-1999, 2002-2004, 2007-2009, 2012-2013, 2015-2016], or on the covariates).

Figure 2.. Trajectories of Alternative Healthy Eating Index (AHEI) Score Between 1991-1993 and 2002-2004 by Incident Dementia Status

The shaded areas represent the 95% confidence intervals (estimated using the MARGINS command in Stata 15.1). The linear mixed-effect model included time since 1991-1993, time squared, age, sex, race/ethnicity, incident dementia status, and their interactions with time and time squared. Among the patients diagnosed as having dementia, the median follow-up was between 1991-1993 and dementia was diagnosed at 20.5 years (interquartile range, 17.7-22.7 years). Among the patients without dementia, the median follow-up was 24.8 years (interquartile range, 24.4-25.2 years).