Decrease of free thyroxin in serum of lactating women.

Abstract

We measured thyroid hormones and thyroxin-binding proteins in serum from 62 normal lactating and 52 nonlactating women at three months postpartum, and compared these values with those for 42 nonpregnant control women of similar age. Mean thyroxin concentrations in the lactating and nonlactating women were significantly (P less than 0.001) lower than that of the nonpregnant controls, but there was no significant difference (P greater than 0.2) in triiodothyronine concentration among these three groups. Free T4 concentration was significantly (P less than 0.01) lower in lactating women than in controls. The reverse-T3 concentrations in both lactating and nonlactating women were significantly (P less than 0.001) lower than in controls, and were significantly (P less than 0.001) lower in lactating than in nonlactating women. The concentration of thyroxin-binding globulin was significantly higher in lactating women than in controls, and the albumin concentration was significantly lower in women postpartum than in controls. Evidently, regulation of thyroid hormone in women postpartum, especially during lactation, differs from that in nonpregnant women.

Estimation of energetic condition in wild baboons using fecal thyroid hormone determination

“…However, in contrast to our predictions, we found that pregnant and lactating females had lower mT3 concentrations than cycling females. Lower mT3 in lactating female baboons, while in disagreement with data in wild howler monkeys (Dias et al, 2017), agrees with previous reports in humans (Iwatani et al, 1987; Yamamoto et al, 1979). This decrease in T3 levels is unexpected in the context of the high energetic demands of lactation, and may reflect energy conservation strategies on the part of the mother.…”

“…We predicted that mT3 concentrations should be lower during the dry season when food availability was reduced, as has been shown by other studies (Ayres et al, 2012; Cristobal-Azkarate et al, 2016; Joly et al, 2015; Schaebs et al, 2016; Wasser et al, 2010; see also review by Chatzitomaris et al, 2017). We also predicted that because of the high energetic costs of pregnancy and lactation, mT3 concentrations should be higher in pregnant and lactating females than in cycling females, as shown for human and non-human primates (Chatzitomaris et al, 2017; Dias et al, 2017; Glinoer, 1997, but see also Iwatani et al, 1987; Yamamoto et al, 1979 for an opposite pattern during lactation in humans).…”

Iodine Status and Thyroid Function in Lactating Women and Infants – a Survey in the Zagreb Area, Croatia

“…No specific reference ranges for thyroid function tests are available for LW. Lower mean tT4 concentrations have been reported in LW compared with non-pregnant, non-lactating women ( 29 , 30 ). The thyroid hormone profile in LW resembles hypothyroid or iodine deficiency state with low T4 and low reverse T3 ( 29 ).…”