The proportion of plant-based food consumption during midlife and cognitive health in later life in Australian women: data from the Women's Healthy Ageing Project (WHAP).

Purpose: Plant-based food (PBF) is well-known for its benefits for physical health; however, its impacts on brain health are less well understood, especially in ageing women. This study aimed to examine the association between different proportions of midlife daily PBF intake and late-life cognitive health among ageing Australian women.

Methods: This study used data of 186 women who had dietary assessment at baseline (1998, aged 52-63) and cognitive assessments at follow-up (2012, aged 66-77) from the Women's Healthy Ageing Project (WHAP). The cohort was divided into quartiles according to the proportions of PBF in their daily diet at baseline. Late-life cognitive function was assessed by Global cognitive composite score (GCCS)-a summary of z-scores of 13 cognitive tests of the Cogstate battery. Three regression models were conducted: unadjusted (N = 186), partially adjusted (age, education, energy intake; N = 186), and fully adjusted (age, education, energy intake, BMI, physical activity, smoking, APOE 4 allele status, N = 165).

Results: In unadjusted and partially adjusted models (N = 186), women in the third quartile (Q3) (second highest consumption of PBF during midlife) had significantly higher GCCS in later life compared to those in the lowest quartile (Q1) (B = 0.39, 95% CI [0.13; 0.66]; p = 0.004 for the unadjusted model; B = 0.34; 95% CI [0.08; 0.61]; p = 0.012, for the partially adjusted model). However, this association was no longer significant in the fully adjusted model (N = 165) (B = 0.25; 95% CI [- 0.02; 0.51]; p = 0.07), where APOE 4 allele status emerged as a significant predictor (B = - 0.25, 95% CI [ - 0.45; - 0.04]; p = 0.02). This change may reflect the reduced statistical power due to smaller sample size and the confounding effect of the genetic risk factors. Among APOE 4 carriers, higher PBF quartiles (Q2-Q4) each predicted greater GCCS in unadjusted analyses; in the adjusted model, Q3 versus Q1 remained significant, but the overall model did not reach significance. Investigation into the change in PBF consumption from midlife to late-life revealed no association with late-life cognitive health.

Conclusion: Midlife PBF consumption did not show a significant independent association with late-life cognitive health after fully adjustment for confounders in this cohort of older Australian women. However, these findings should be interpreted with caution as the small sample size and confounding factors might have affected the ability to detect a subtle effect of PBF on cognition. Future research is needed to explore this relationship in larger, more diverse samples and its complex interaction with genetic risk factors.