# Disentangling the relationship between glucose, insulin and brain health: A UK Biobank study

## TL;DR

This study finds that higher post-meal glucose levels are linked to increased Alzheimer's risk, but not to brain structure changes, suggesting a new pathway for dementia prevention.

## Contribution

The study uses genetic data to show a novel link between postprandial glucose and Alzheimer's risk, independent of brain atrophy.

## Key findings

- Higher 2-h post-load glucose is associated with a 69% increased Alzheimer's risk.
- Fasting glucose and insulin levels do not affect brain structure volumes.
- Postprandial hyperglycaemia may contribute to Alzheimer's risk independently of structural brain changes.

## Abstract

Glycaemic traits are associated with poorer brain health and dementia risk. Recent advances in genetic instruments for specific glycaemic markers enable an in‐depth investigation of the likely nature of associations and underlying mechanisms between diabetes‐related mechanisms and brain health and dementia.

We used two‐sample Mendelian randomisation (MR) in the UK Biobank (UKB) (maximum N = 357 883 White British, mean age 56.9 years, 54% female) applying inverse‐variance weighted MR as our main estimator alongside MR‐Egger, weighted median estimator (WME) and Mendelian Randomization Pleiotropy RESidual Sum and Outlier (MR‐PRESSO) as sensitivity tests. Instruments were 53 insulin resistance, 109 fasting glucose, 48 fasting insulin and 15 2‐h post‐load glucose genetic variants with variant–outcome effects estimated adjusting for 10 PCs. We checked core MR assumptions and sought to replicate results in an independent Alzheimer's dementia genome‐wide association study (GWAS).

In UKB, higher 2‐h post‐load glucose was associated with a 69% increased Alzheimer's dementia risk (odds ratio 1.69 [95% confidence interval 1.38–2.07]), though this did not replicate in an independent GWAS. Fasting insulin, fasting glucose and postprandial glucose did not influence total brain, hippocampal or white‐matter hyperintensity volumes.

The association between elevated 2‐h post‐load glucose and increased Alzheimer's risk supports a potential role for postprandial hyperglycaemia in dementia. The lack of associations between fasting or postprandial glucose and hippocampal, total‐brain or white matter hyperintensity volumes suggests this risk may operate independently of gross structural atrophy.

Genetically proxied postprandial hyperglycaemia contributes to increased Alzheimer's risk in mid‐life, warranting replication in other populations and ancestries to confirm and clarify underlying mechanisms.