Exact profiles of 13CO2 recovery in breath air after per oral administration of [13C]methacetin in two groups of different ages

The aim of this study is to determine if age is a factor influencing the results of a [¹³C]methacetin breath test (¹³C-MBT). Two groups of healthy volunteers, each comprising six men and six women, but differing in average age (Y=young, 25.1±0.6 years, MA=middle-aged;, 46.0±2.1 years) orally took 75 mg [¹³C]methacetin. Samples of expiratory air for ¹³CO₂ measurement were collected up to 48 h after intake of the substrate. A maximum momentary ¹³CO₂ breath exhalation of 37.0±2.6%dose/h was observed at 18 min (median, range: 9–30 min) in the young subjects and of 38.4±2.5%dose/h at 18 min (median, range: 12–30 min) in the middle-age volunteers. The cumulative ¹³C elimination in expiratory air was statistically significantly higher in the MA compared with the Y group as from 75 min up to 180 min, indicating a greater microsomal metabolic efficiency of the liver in the middle-aged healthy subjects. Gender, use of hormonal contraception, cigarette smoking, or body mass index did not modify the age-related effect on the cumulative ¹³C elimination in breath air. The study results imply a necessity of composing control groups well matched with regard to the age structure for a proper interpretation of clinical ¹³C-MBT results.