A study led by researchers from Japan reveals U-shaped associations between body mass index (BMI) and serum liver enzyme levels, introducing new insights on the relationship between weight and liver health.
The research, which analyzed data from 15,464 individuals at the Murakami Memorial Hospital, found interesting patterns linking liver enzyme levels—especially aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyl transferase (GGT)—to varying BMI levels.
According to the analysis, informative inflection points were identified: for AST serum levels, the turning points were at BMI values of 19.0 and 23.3 kg/m²; for ALT serum levels, the points were at 19.0 and 23.1 kg/m²; and for GGT serum levels, the inflection point was at 19.5 kg/m². This pattern confirms the U-shaped association, indicating both lower and higher BMI could correlate with elevated liver enzyme levels.
Authors of the article expressed, "Our study is the first to identify a U-shaped association between BMI and serum levels of liver enzymes in the general population, which suggests new targets for regulating liver enzyme levels."
This finding is particularly significant as it challenges earlier assumptions about the linear relationship between obesity and liver health. Historically, studies have suggested obesity and higher BMI are strongly correlated with increased liver enzyme levels, commonly linked to fatty liver disease prevalence.
The study also highlights the prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD), closely associated with obesity, leading to increased serum liver enzyme levels even among individuals classified as normal weight.
To understand these relationships, the researchers used smooth curve and multiple linear regression analyses, adjusting for various factors such as age, sex, and lifestyle habits, including alcohol consumption and smoking status. Notably, they found sex, fatty liver condition, and smoking significantly modified the associations between BMI and liver enzyme levels. For example, the positive correlation between BMI and AST and ALT serum levels was more pronounced among men and individuals with fatty liver. Conversely, alcohol consumption influenced the relationship between BMI and GGT serum levels irrespective of the actual BMI.
These findings suggest the importance of monitoring liver health across different weight categories, emphasizing the necessity not only for weight loss interventions for the overweight but also strategies to address malnutrition or weight gain among those with lower BMI. "Weight gain can exacerbate fatty liver and lead to rapid increases in AST and ALT serum levels," explained the authors, pointing to the dual nature of the health risk surrounding abnormal liver enzyme levels.
With the rising incidences of abnormal liver enzyme levels even among lean individuals, the research stresses the potential value of addressing lifestyle factors such as diet and nutrition to support liver health comprehensively.
Lead researchers assert, "Our findings help guide lifestyle adjustments, showing the clear need for individuals to maintain healthy BMI ranges to protect liver function." Their work supports the assertion not only to manage weight for those who are overweight but also to focus on nutritional support for individuals with lower body weights who may experience health complications from malnourishment.
Despite the valuable insights offered, the authors note certain limitations of the study, including the cross-sectional design, which establishes association but not causation. Therefore, they propose future prospective investigations to validate their findings and explore additional underlying mechanisms influencing liver enzyme levels.
Overall, as obesity and liver diseases remain pressing public health issues, this research adds important knowledge to the discourse, reiteratively illustrating the significance of both extremes of BMI on liver health.