# Health risk behaviours, mental health and HbA1c: an overview of reviews of observational studies

## TL;DR

This umbrella review summarizes observational studies linking health risk behaviors like smoking and poor sleep to HbA1c levels and mental health.

## Contribution

It provides a comprehensive overview of existing systematic reviews on HRBs and HbA1c, highlighting gaps and bidirectional relationships.

## Key findings

- Poor sleep, poor diet, and smoking are linked to worse HbA1c levels.
- A bidirectional relationship exists between depression and HbA1c.
- There is a lack of systematic reviews on alcohol and exercise in relation to HbA1c.

## Abstract

To implement an overview of reviews that discuss the current state of syntheses (such as systematic reviews) of only observational studies on health risk behaviours (HRBs), including smoking, alcohol intake, poor sleep, poor quality diet, common mental health problems (depression and anxiety), and glycated haemoglobin (HbA1c), while excluding synthesis of clinical trials.

Overview of reviews or umbrella review following Preferred Reporting Items for Overviews of Reviews (PRIOR) guidelines.

PubMed, Scopus, Web of Science, PsycINFO-PsychArticles and Epistemonikos, searched from January 2013 to 30 June 2025.

We included systematic reviews and meta-analyses of observational studies that assessed the relationship between HRBs—including smoking, alcohol intake, poor sleep, poor quality diet, physical activity and common mental health problems such as depression and anxiety—and HbA1c. Reviews of clinical trials were excluded.

We synthesised systematic reviews and meta-analyses on the above topic from five databases following the PRIOR protocol. Two independent reviewers screened titles, abstracts and full texts using standardised methods. Data extracted included study design, exposures, outcomes and population characteristics. Risk of bias was assessed using the AMSTAR-2 tool. Overlap across reviews was evaluated using the corrected covered area metric.

Eight systematic reviews were included in the final synthesis, encompassing a total sample size of around 307 019 individuals. The study highlights a significant paucity of systematic reviews of observational studies in this area, with no reviews on alcohol and exercise. The existing evidence on poor sleep, poor quality diet and smoking points towards these HRBs leading to worse HbA1c. A bidirectional relationship was found between depression and HbA1c.

This umbrella review highlights the significant association between HbA1c and key health risk factors underscoring the importance of observational studies, highlighting their ability to capture real-world conditions and complex interactions. While in agreement with existing study designs, this review provides convergent evidence of the critical role of HRBs in managing HbA1c levels.