Alkaline Phosphatase and Hyperphosphatasemia in Vitamin D Trial in Healthy Infants and Toddlers.

Context: Childhood hyperphosphatasemia is usually transient and may be associated with infections. It remains less well known how hyperphosphatasemia is related to growth and bone mineralization.
Objective: We explored alkaline phosphatase (ALP) concentrations and prevalence of hyperphosphatasemia, and their association with vitamin D, growth, infections, and bone parameters in healthy children.
Methods: The study was a secondary analysis of a vitamin D intervention trial. Participants received vitamin D3 10 or 30 µg daily from age 2 weeks to 2 years. Children with data on ALP at 12 and/or 24 months (n = 813, girls 51.9%) were included. Anthropometrics and bone parameters were measured at 12 and 24 months. Infections were recorded prospectively by the parents.
Results: Boys had higher ALP than girls at 12 months (median [IQR] 287 [241-345] U/L vs 266 [218-341] U/L; P = .02). At 24 months concentrations were lower than at 12 months (240 [202-284]; P < .001) but without sex difference. The prevalence of hyperphosphatasemia (ALP > 1000 U/L) at 12 months was 5.3% and at 24 months 0.6%. Body size, growth rate, and bone mineral content associated positively with ALP, while vitamin D intervention had no effect. Infants with hyperphosphatasemia were smaller than infants with ALP ≤ 1000 U/L. Hyperphosphatasemia was not associated with previous infections.
Conclusion: Approximately 5% of infants had hyperphosphatasemia at 12 months, but <1% at 24 months. ALP concentrations and hyperphosphatasemia were associated with sex, anthropometry, and bone mineralization. Infections did not contribute to hyperphosphatasemia.
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