It is well known that tetany in infants shows a striking seasonal incidence. The condition is rare during the summer and autumn months, but is common in the winter and particularly in the spring. As infantile tetany is associated with a diminution in the calcium content of the serum, it seemed of interest to determine whether a fluctuation in the serum calcium of infants at various times of the year is physiologic. A seasonal tide has been demonstrated by Hess and Lundagen1 for the inorganic phosphorus of infants' blood, corresponding to the increased incidence and severity of rickets during the winter and spring months. Grant and Gates2 have observed fluctuations in the serum calcium concentration of rabbits with low values in January and with high values in May and November.
The infants whom we studied ranged in age from 3 to 24 months, but most of the observations
BAKWIN H, BAKWIN RM. SEASONAL VARIATION IN THE CALCIUM CONTENT OF INFANTS' SERUM. Am J Dis Child. 1927;34(6):994-999. doi:10.1001/archpedi.1927.04130240073010