Circadian rhythm of intestinal absorption of xylose in man.

In sixteen volunteers, 10 g xylose tests were performed six times on different days at the following hours: 6 a.m., 10 a.m., 2 p.m., 6 p.m., 10 p.m. and 2 a.m. Xylose levels were examined in duplicate, both in blood and urine samples according to Roe and Rice. Generally, the results indicated a greater availability (i.e. absorption) of xylose in the morning than at the other times. But a circadian rhythm was detected only for two out of several examined parameters. These were: 1) blood xylose levels 90 min after ingestion time, with mesor M (mg/100 ml) = 18.8, with amplitude, A = 2.3 and with acrophase, phi = 12(22) (95% conf. limits: 7 a.m. to 4(19) p.m.), and 2) the peak of serum concentration of xylose with M = 21.2, with A = 2.2 and with phi = 11(16) a.m. (95% CL: 6(16) a.m., 5(35) p.m.).