Good glycaemic control helps slow brain ageing

Improved glycaemic control is a big contributor to the neuroprotective effects of Mediterranean (MED) and green-MED diets on brain age, a study has shown. In addition, polyphenols-rich diet components such as Mankai and green tea help prevent brain ageing.

"If confirmed by additional studies, this finding may indicate an accessible, low-risk, and practical approach to attenuating age-related neurodegeneration, which could hold potential clinical significance for future applications in cognitive health,” the investigators said.

This study was a post hoc analysis of the 18-month DIRECT PLUS trial, in which participants were randomized to healthy dietary guidelines, MED diet, or green-MED diet, which were high in polyphenols and low in red meat. 

Participants in both MED groups consumed 28 g of walnuts per day, and those in the green-MED group further consumed green tea (3–4 cups per day) and Mankai green shake (Wolffia globosa aquatic plant).

The investigators collected blood samples through the intervention and followed brain structure volumes by MRI. They used hippocampal occupancy (HOC) score (hippocampal and inferior lateral-ventricle volumes ratio) as a neurodegeneration marker and proxy for brain age. Multivariate linear regression models were also constructed.

A total of 284 participants (mean age 51.1 years, BMI 31.2 kg/m², 88 percent male, HbA1c 5.48 percent, APOE-ε4 genotype 15.7 percent) were included, of whom 224 completed the trial with eligible whole-brain MRIs. [Am J Clin Nutr 2024;120:1029-1036]

Individuals who had a younger brain age, as shown by higher HOC deviations, presented with lower body weight (r, –0.24, 95 percent confidence interval [CI], –0.298 to –0.101), waist circumference (r, –0.207, 95 percent CI, –0.310 to –0.103), diastolic blood pressure (r, –0.186, 95 percent CI, –0.304 to –0.071), and systolic blood pressure (r, –0.189, 95 percent CI, –0.308 to –0.061).

Diabetes status

A younger brain age was also observed in individuals with lower insulin (r, –0.099, 95 percent CI, –0.194 to –0.004) and HbA1c levels (r, –0.164, 95 percent CI, –0.337 to –0.006).

Factors such as improved HbA1c (β, –0.254, 95 percent CI, –0.392 to –0.117), HOMA-IR (β, –0.200, 95 percent CI, –0.346 to –0.055), fasting glucose (β–0.155, 95 percent CI, –0.293 to –0.016), and C-reactive protein (β, –0.153, 95 percent CI, –0.296 to –0.010) each contributed to greater changes in HOC deviations (ie, slower brain-age decline) after 18 months.

Improvements in diabetes status likewise contributed to greater changes in HOC deviation relative to no change in diabetes status (0.010, 95 percent CI, 0.002–0.019) or with an unfavourable change (0.012, 95 percent CI, 0.002–0.023). Moreover, a decline in HbA1c correlated with greater deviation changes in the thalamus, cerebellum, and caudate nucleus (p<0.05).

Notably, individuals who regularly consume Manka and green tea (green-MED diet components) showed greater HOC deviation changes beyond weight loss.

“Younger brain age was driven by greater consumption of high polyphenols: green tea and Mankai,” the investigators said. “Our findings suggest a potential mechanistic pathway for driving the favourable impact of high-polyphenol diets.”

Additionally, consuming polyphenols-rich foods, such as green tea and Mankai, could improve the blood–brain barrier, lower blood pressure, and prevent age-related brain atrophy.