Effects of the length of radioiodine treatment of hyperthyroidism on the distribution of blood levels of calcium and phosphorus as a function of sex and age

: An evaluation was made of the incidence of hypoparathyroidism after 131I management of hyperthyroidism and of the effect of irradiation on the relation between blood calcium, phosphorus and proteins and age in normal subjects. 356 treated patients and 216 controls were examined. Serum calcium was determined from 2 to 6 yr after treatment. It was found that calcium values decrease with age in males, wherease in women this phenomenon is less marked and, indeed, is no longer apparent over the age of 30. In the normal male, phosphrous also decreases with age, while in females there is a fall until the age of 30-40 yr, followed by a rise. Only 1 subject with a value of 8.45 mg calcium/100 ml was noted in the treated group and there was no significant difference between the means for the two groups, suggesting that parathyroid insufficiency is a virtually non-existent complication of the 131I treatment of hyperthyroidism. The relation between blood calcium and phosphorus and age in the treated group was examined with reference to subjects with normal thyroid function only. In the case of calcium, values were no longer related to age after treatment in males, while phosphorus values fell to below those observed in females, coupled with an increase in function of age as in women, though this itself was not statistically significant. Treatment also suppressed the relation between total blood proteins and age noted in the normal male. None of the parameters considered displayed any significant changes in the treated females. It would thus seem that 131I abolishes the differences in blood calcium and phosphorus mean values and age-linked patterns normally found between males and females.