Midlife Diet Shows No Association with Subsequent Risk for Dementia

Diet quality evaluated during midlife showed no significant association with any subsequent risk of developing dementia, according to a UK study published in JAMA.

In this population-based cohort study, known as Whitehall II and established in 1985-1988, researchers assessed diet quality during midlife by querying 8,225 participants (mean age, 50, 69.1% male) without dementia using the Alternate Health Eating Index (AHEI, score range, 0-110). The AHEI score consists of 11 components: six components for which the highest intake is seen to be ideal (vegetables, fruits, whole grains, nuts and legumes, long-chain omega-3 fatty acids, and polyunsaturated fatty acids [excluding long-chain omega-3 polyunsaturated fatty acids]); and four components for which avoidance or the lowest intake is seen to be optimal (sugar-sweetened drinks and fruit juice, red and processed meat, trans fat, and sodium). Dietary intake was appraised during 1991-1993, 1997-1999, and 2002-2004 using a machine-readable food frequency questionnaire (FFQ). The primary outcome was incident dementia and the secondary outcome was cognitive decline between 1997-1999 and 2015-2016.

No Diet/Dementia Correlation Observed

Among all participants, a total of 344 cases of incident dementia were recorded during a median follow-up of 24.8 years. Researchers observed no difference in the incidence rate for dementia in the tertiles of AHEI exposure during 1991-1993, 1997-1999 (average follow-up, 19.1 years), or 2002-2004 (average follow-up, 13.5 years). Juxtaposed with an incidence rate for dementia of 1.76 (95% CI:1.47-2.12) per 1,000 person-years in the lowest tertile of AHEI 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.

Moreover, compared with the lowest 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.

Furthermore, 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]).

Diet and Cognitive Outcomes Connection Remains Unclear

“The lack of a significant association between early midlife diet and cognitive outcomes is unlikely to be due to poor measures of diet quality because diet was associated with mortality in the present study,” stated the authors of this study. “Whether a healthy diet plays a role in shaping cognitive outcomes in combination with other healthy behaviors or in subgroups at increased risk for dementia remains unclear.”