Hemoglobin synthesis rates in young trained and untrained males and females are not different.

We employed deuterated water (2H2O) to compare the fractional synthetic rate (FSR) of hemoglobin in trained (n = 10) and untrained humans (n = 10). Participants had a mean V̇O2max of 49.8 [SD: 10.9] mL/kg/min, hemoglobin mass of 775 [180] g, and red blood cell volume of 2370 [550] mL. After a loading dose, participants ingested 2H2O daily for 28 days to maintain a stable 2H body water enrichment (~0.5 atom percent excess (APE)), as measured in saliva samples. 2H-enriched alanine APE was measured in RBC protein using gas chromatography pyrolysis isotope ratio mass spectrometry. The increase in APE for Hb protein was nonlinear for the first 2 weeks but stabilized from day 14 to day 28, with mean APE reaching 0.033 [0.005]% on day 28. Hb FSR calculated over this 2-week period was 0.84 [0.15]%/day, which equated to an Hb absolute synthetic rate of 6.5 [2.2] g/day and a lifespan of 126 [30] days. Hb FSR was not different between trained (0.83 [0.19] %/day) and untrained (0.86 [0.24] %/day, p = 0.81) individuals or between males (0.80 [0.25] %/day) and females (0.88 [0.17] %/day, p = 0.24). Endurance training and sex did not affect Hb FSR. The 2H2O method to measure Hb FSR is feasible in humans.