Alteration in Elemental Body Composition in Thyroid Disorders1

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Abstract
Recent developments in the technique of total-body neutron activation analysis (TBNAA) have made it possible for the first time to measure precisely total body levels of calcium, phosphorous, sodium and chlorine in human subjects. This technique has been employed here to evaluate the degree of skeletal demineralization in patients with thyroid disorders both prior to and following the initiation of therapeutic regimes. The loss of Ca in white thyrotoxic patients was found to average 9.4% in terms of expected normal values. The Ca and P levels of 2 black patients with thyrotoxicosis were within the range of their expected normal values. The expected normal Ca values (CaP) were empirically derived from the height and potassium levels of 14 normal subjects. Following the institution of a therapeutic program, whether with drugs, surgery or 131I treatment, body Ca increased 8.4% on the average in the first 9 months. At the same time Na decreased along with the P/Ca ratio, and lean body mass (measured by K) and body protein (measured by N) increased. Normal Ca and P levels were noted in the majority of hypothyroid patients, but were lower in 2 post-menopausal female patients. The mean P/Ca ratio was below normal in the patients with hypothyroidism. The mean Ca level dropped 7.6% of the CaP following initiation of therapy, and the P/Ca ratio was elevated. Na/K level was also elevated in most patients; no consistent change occurred with therapy. Total body K was decreased following initiation of therapy, reflecting the catabolic effect of thyroxine. Measurement of skeletal mineralization by quantification of Ca and P by TBNAA technique in thyroid dysfunction appears useful in analyzing the mechanism of the disorder and in evaluation of therapeutic programs.

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