Chronobiology of serum iron concentration in subjects of different ages at different geographic locations.

The circadian rhythm in serum iron concentration was studied in 61 elderly men (74 +/- 6 years of age) and 93 women (78 +/- 8 years of age) in Bucharest, Romania, in 81 clinically healthy boys and 103 girls (11 +/- 1.5 years of age) in Tîrgovişte, Romania, in 4 elderly men and 19 women (71 +/- 5 years of age) and in 75 young-adult men (24 +/- 11 years of age) and 52 women (24 +/- 9 years of age) in St. Paul, Minnesota, USA. Six samples were obtained from each subject around a 24-hour span. The sampling sessions in the elderly subjects in Romania and in the children extended over all four seasons. A circadian rhythm statistically verified by Cosinor analysis was evident in all groups in both locations. A statistically significant sex difference with lower circadian mean (mesor) and a lower amplitude in the women was found in the Romanian elderly subjects. The children in Romania showed no sex difference in any circadian rhythm parameters. The young adult subjects in Minnesota showed a significantly higher mesor and a phase delay in the men as compared with the women. The elderly subjects of both sexes at both geographic locations had a lower circadian mesor than the young adults and the children. In the Romanian elderly subjects also the circadian amplitude was lower, which was not the case in the Minnesotans. While the acrophase in the elderly subjects and in the children in Romania was comparable (0928 and 0932 local time resp.), the young adults in Minnesota showed in comparison to the Romanians a phase delay (1132 local time) and the elderly in Minnesota showed a phase advance (0732 local time) in comparison to all other groups. The latter finding will have to be confirmed by more extensive studies. In the elderly subjects in Romania the circadian rhythm in serum iron concentration was in phase with the circadian rhythms in total serum bilirubin and alkaline phosphatase but showed significant phase differences from the circadian rhythms in serum albumin, urea nitrogen (BUN), gammaglutamyl transferase (Gamma-GT), serum globulins, glucose, insulin and total serum proteins. The elderly subjects in Romania showed a statistically significant circadian phase delay in summer as compared to fall but showed no seasonal variation of the mesor. The children showed a circadian phase advance in fall as compared to the other seasons and a seasonal variation of their mesor with higher values in spring and summer as compared with winter and fall.(ABSTRACT TRUNCATED AT 400 WORDS)