Starvation-induced alterations of circulating thyroid hormone concentrations in man

Serum concentrations of triiodothyronine, thyroxine and TSH were examined in seven men and seven women of normal weight during a 60-hr fast to indicate that a decreased peripheral conversion of T4 to T3 is the most likely mechanism responsible for this change.

Abstract

Serum concentrations of triiodothyronine (T3), thyroxine (T4), and TSH were examined in seven men and seven women of normal weight during a 60-hr fast. Similar studies were conducted in two women who received daily for 1 mo before and during a similar fast, 0.4 mg and 0.5 mg of 1-thyroxine. The serum concentrations of T3 decreased in each of the untreated normal subjects (sign test of significance, P less than 0.001). The mean control concentration of T3 in women was 152 +/- 9 ng/100 ml (X +/- SEM); after 24 hr of fasting, 131 +/- 31 ng/100 ml; and at the termination of the fast, 90 +/- 15 ng/100 ml. The latter value differed from the control value with a p value of less than 0.01. Similar changes of T3 concentration occurred in men (mean basal T = 160 +/- 11 ng/100 ml; mean at termination of fast = 87 +/- 16 ng/100 ml). The range of decrease for T3 in all subjects varied from 24% to 55%. The mean T4 concentration at the beginning of the fast was 6.9 +/- 0.9, and at the termination of the fast, 7.5 +/- 0.6 (p = NS). TSH concentrations remained unchanged (Control, 3.8 +/- 0.45 muU/ml; at 60 hr, 4.0 +/- 0.26 muU/ml, p = NS). Studies in two women who received, before and during a fast, T4, indicate that a decreased peripheral conversion of T4 to T3 is the most likely mechanism responsible for this change.