Causal associations between urinary sodium with body mass, shape and composition: a Mendelian randomization study

Area of Science:

• Genetics
• Epidemiology
• Metabolic Health

Background:

• Observational studies suggest links between urinary sodium (UNa) and obesity, but findings may be confounded.
• Mendelian randomization (MR) can assess causal relationships, overcoming limitations of observational data.

Purpose of the Study:

• To investigate the causal associations between urinary sodium (UNa) and obesity metrics including body mass index (BMI), body fat (BF) percentage, and waist-to-hip ratio (WHR).
• To explore sex-specific effects and the bidirectional relationship between UNa and BMI.

Main Methods:

• A two-sample Mendelian randomization (MR) study utilizing genome-wide association study (GWAS) data.
• Selection of single nucleotide polymorphisms (SNPs) for UNa and obesity traits, with adjustments for potential pleiotropy and estimated glomerular filtration rate (eGFR).
• Inverse-variance weighted (IVW) MR as primary analysis, with MR-Egger as sensitivity analysis.

Main Results:

• Urinary sodium (UNa) was causally associated with increased BMI and body fat (BF) percentage in both men and women.
• UNa significantly increased BMI-adjusted waist-to-hip ratio (WHR) in men, but not in women.
• A bidirectional causal association was observed, with BMI also causally increasing UNa.

Conclusions:

• High sodium intake is a causal factor for increased BMI and body fat percentage.
• Sodium intake influences male body shape through BMI-adjusted WHR, with no significant effect on female body shape.
• Simultaneous implementation of salt reduction and weight management strategies is recommended to address the interplay between BMI and UNa.