Modifiable Lifestyle Factors, Left Atrial Indices, and Atrial Fibrillation.

Body mass index, physical activity intensity, and alcohol intake were each significantly associated with larger LA volumes and smaller LA emptying fractions.

• Study included 37,701 UK Biobank participants without prevalent AF and with cardiac magnetic resonance imaging data
• Associations were found in multivariable analyses controlling for other factors
• BMI was measured by study personnel, while lifestyle factors were obtained from baseline questionnaires
• Cardiac MRI was performed a median 8.9 years (IQR, 7.4–10) after baseline lifestyle factor assessment

Cumulative pack-years of smoking were associated with smaller LA volumes and smaller LA emptying fractions.

• This finding was opposite in direction to the associations seen with BMI, physical activity intensity, and alcohol intake
• Association was identified in multivariable analyses
• LA emptying fraction mediated part of the smoking-AF relationship (see mediation finding below)

Coffee consumption was not significantly associated with LA volumes or LA emptying fraction.

• Coffee consumption was assessed via baseline questionnaire
• No significant associations were found in multivariable analyses
• This null finding was in contrast to the significant associations seen with BMI, physical activity, alcohol, and smoking

Larger LA maximal volume, larger LA minimal volume, and lower LA emptying fraction each statistically mediated approximately one quarter of the association between increased BMI and incident AF.

• LA maximal volume mediated 25% of the BMI–incident AF association
• LA minimal volume mediated 28% of the BMI–incident AF association
• LA emptying fraction mediated 26% of the BMI–incident AF association
• Each LA index was evaluated in a separate mediation model

Lower LA emptying fraction mediated 27% of the association between smoking and incident AF.

• Mediation was evaluated in a separate model for LA emptying fraction and the smoking–AF association
• This finding suggests that smoking-related changes in LA function, rather than LA size alone, contribute to AF risk
• Cumulative pack-years were used as the smoking exposure measure