The Influence of Sleep, Work, Diuresis, Heat, Acute Starvation, Thiamine Intake and Bed Rest on Human Riboflavin Excretion

Abstract

Urinary excretion of riboflavin was studied in normal men under a variety of environmental conditions. Diurnally, meals tended to increase and sleep to retard the rate of excretion. Short periods of hard physical work were accompanied by a decreased excretion of riboflavin which appeared to be related to decreased renal plasma flow. Diuresis, induced with water, was without effect on the excretion of riboflavin. Acute starvation increased the excretion of riboflavin approximately three-fold when men performed hard physical work for three days and approximately 5-fold when starved for 7 days under sedentary conditions. Heat stress (49°C and 30% relative humidity 10 hours per day for 6 days) increased the mean excretion of riboflavin gradually from 443 µg per day initially to a maximum of 692 µg per day. Enforced bed rest increased the mean excretion of riboflavin by 487 µg per day in spite of a concomitant reduction in riboflavin intake of 0.31 mg per day. Thiamine deficiency alone led to an immediate increase in riboflavin excretion. In combined thiamine and riboflavin deficiency, the increased excretion of riboflavin was observed only after 4 weeks of deprivation. In both cases, the increased excretion of riboflavin was restored to normal when the subjects were given 5 mg per day of thiamine.