LONGITUDINAL-STUDY OF URINARY HYDROXY-PYRIDINIUM CROSS-LINKS AND GROWTH IN HEALTHY INFANTS - HIGHER VALUES WITH BREAST-FEEDING AND AFTER DAYTIME SLEEP

Urinary pyridinoline and deoxypyridinoline crosslinks (crosslink) are excreted when bone is resorbed. The aims of this study in healthy infa nts were to determine whether crosslinks a) could predict growth veloc ity, b) are variable due to circadian rhythm, and c) differ in infants who were either breast-fed or formula-fed. In 78 healthy infants (48 male; 30 female) urine samples were collected and anthropometric measu rements were taken at 2, 3, 4, 5, 6, 8, 10 and 12 months of age. In ad dition, a total of 25 samples were collected during the day (0700-2000 ) in 5 of the infants to determine circadian rhythm of crosslink excre tion. Crosslink excretion decreased (p < 0.001) with age between 2 and 12 months. Pyridinoline excretion showed a significant, but weak corr elation (r greater than or equal to 0.21; p < 0.05) with linear growth velocity and weight velocity in the subsequent month until 6 months o f age, and no correlation thereafter. Infants studied for circadian rh ythm showed a 63% greater (p < 0.05) rate of pyridinoline excretion af ter a nap as compared to the 13-hour mean value. In a subset of infant s whose energy intake was exclusively from breast milk (BF, n = 23) or formula (FF, n = 10), crosslink excretion was greater in BF infants a t 3 months of age (p < 0.05). The correlations between crosslink excre tion and growth parameters indicate that crosslinks may be useful as a marker of growth in infant populations. However sources of variation in crosslink excretion, such as circadian rhythm and diet may limit th eir utility to predict growth in an individual infant. These factors s hould be considered in future studies examining markers of bone turnov er in infants.