Blueberry Supplementation in Midlife for Dementia Risk Reduction

Interventional human study in overweight, non-diabetic adults aged 50 to 65 years with subjective cognitive decline and insulin resistance, living in the Cincinnati, Ohio, USA area. The active blueberry arm was compared with placebo, and participants avoided berry fruits for 14 days before enrollment and during the intervention.

Blueberry powder made from whole, freeze-dried blueberry was given orally once daily for 12 weeks at a dose equivalent to 0.5 cup of whole fruit. The powder was mixed with water and consumed with the morning or evening meal; the comparison group received placebo powder.

Blueberry supplementation produced selective cognitive and metabolic benefits rather than broad improvements. Phonemic lexical access improved significantly, with COWA F(1,24)=10.67, p=0.003, Cohen's f=0.66, and intrusion errors on learning decreased, F(1,24)=4.69, p=0.04, Cohen's f=0.20. Memory encoding-related complaints also improved on EMQ factor 3, F(1,24)=4.93, p=0.03, Cohen's f=0.45, and fasting insulin decreased at week 12, F(1,24)=4.62, p=0.04, to 8.3 µU/mL. There were no significant effects for category fluency, verbal paired associate learning, lipids, glucose, glycated hemoglobin, or most other metabolic and anthropometric outcomes.

The intervention was short at 12 weeks, and the available data suggest a small sample, with incomplete reporting of active-arm sample size and a mitochondrial subset analyzed in only part of the cohort. Benefits were selective rather than consistent across cognitive and metabolic endpoints, which limits confidence in the breadth of effect. Generalizability is also limited to overweight midlife adults with subjective cognitive decline and insulin resistance.