Studies on circadian periodicity of plasma, breast milk and urinary calcium in lactating Indian women.

Circadian periodicity of plasma, breast milk and urinary calcium was studied in six lactating Indian women. Peak plasma calcium was recorded at 2000 with a progressive decline during the rest of the period reaching a minimum at 0800. Breast milk calcium was found to be maximum at 0200 and decreased consistently reaching a minimum at 2000. Maximum urinary calcium was observed at 0600 to 1200 with a minimum excretion at 1800 to 0000. A marked circadian variation during the 24 hour period was noticed in plasma, breast milk and urinary calcium confirming a definite rhythm of endogenous body calcium in lactating Indian women. Thus, there we found significant diurnal rhythm in body calcium at all levels and each of them might be initiating the other rhythm, partly governed by the day-night cycle in tropical conditions.