Abstract
Background: Aspartate aminotransferase (AST) is pivotal in amino acid metabolism. However, the serum activity of AST, which leaks from multiple organs, including liver and skeletal muscle, is unknown in older underweight people, who are at high risk of skeletal muscle mass loss. Therefore, we measured the serum activities of AST and alanine aminotransferase (ALT), a liver-specific transaminase, in a large, community-based cross-sectional study. Methods: Clinical parameters and lifestyles were characterized in 892,692 Japanese people with a wide range of body mass indexes (BMIs; 13–39.9 kg/m2), aged 40–74 years old, who were undergoing a medical checkup. A general linear model was used to calculate the estimated mean of serum AST (EM-AST) in each BMI category after adjustment for confounding factors, including past history of cardiovascular disease and waist circumference. Results: Severe underweight (BMI 13–14.9 kg/m2) was present in 910 subjects (0.1%). Raw serum AST showed a J-shaped relationship with BMI, which was blunted in older subjects (60–74 years), and similar, but less curved relationships were identified for raw serum ALT and gamma-glutamyl transferase. These J-shaped relationships in serum AST were not altered when subjects were classified by sex, past history of cardiovascular and cerebrovascular diseases, and habitual exercise. EM-AST showed a U-shaped relationship, with a minimum at BMI 21–22.9 kg/m2, regardless of age and waist circumference. Conclusions: High serum AST but normal serum ALT is highly prevalent in older underweight people and might reflect skeletal muscle pathology.
Highlights
Serum aspartate aminotransferase (AST) activity is routinely measured worldwide as part of regular medical checkups because it can be rapidly, inexpensively, and reproducibly assayed
Chronic malnutrition involves a shortage of vitamin B6 as well as other nutrients [7,8], which leads to dysfunction of these enzymes and multiple organ defects
The serum activities of these enzymes have not been characterized in older underweight people, who are at a greater risk of skeletal muscle loss, which eventually results in sarcopenia and a higher mortality rate than that of normal-weight people [9,10]
Summary
Serum aspartate aminotransferase (AST) activity is routinely measured worldwide as part of regular medical checkups because it can be rapidly, inexpensively, and reproducibly assayed. The activity of alanine aminotransferase (ALT), a liver-specific transaminase, is measured simultaneously to distinguish hepatic and nonhepatic pathology [3,4,5,6]. These enzymes are important for amino acid degradation and biosynthesis, during which they catalyze the transfer of amino groups from aspartic acid or alanine to ketoglutaric acid to produce oxaloacetic acid and pyruvic acid, respectively [2,3]. Conclusions: High serum AST but normal serum ALT is highly prevalent in older underweight people and might reflect skeletal muscle pathology
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