Vitamin B2 status in athletes and the influence of riboflavin administration on neuromuscular irritability

In order to obtain information on the vitamin B2 status in athletes in training, the following aspects were investigated: in one group of athletes, riboflavinuria at rest, during the autumn and winter months (mean values 23.8 and 9.45 mug/h, respectively); in the second group (n = 18), the activity of the nicotinamide-adenine-dinucleotide-phosphate-dependent red blood cell glutathione reductase (EC 1.6.4.2) and its activation by added flavin adenine dinucleotide. In 8 athletes, activation coefficients higher than 1.25 were found, indicating a biochemical deficiency of riboflavin. Erythrocyte transketolase (EC 2.2.1.1) was activated by more than 25% with added thiamine pyrophosphate in 12 cases. In muscle samples of 10 healthy patients (fresh fractures or removing of metal plates from old fractures), glutathione reductase (mean activity 0.846 +/- 0.458 U/g wet weight) was activated by more than 25% in 5 cases. Administration of 10 mg of riboflavin per os resulted in moderate lowering of neuromuscular irritability (musculi vastus medialis and lateralis quadricipitis) particularly for 0.1-msec rectangular stimuli.