Total triiodothyronine and leptin levels in sedentary ovulatory women and exercising women with ovulatory and luteal phase deficient menstrual cycles

Date of Completion

January 1999

Keywords

Health Sciences, Obstetrics and Gynecology|Biology, Animal Physiology|Women's Studies|Health Sciences, Recreation

Degree

Ph.D.

Abstract

In this study we examined the relationship of menstrual cycle status to thyroid hormones and leptin concentrations in sedentary and exercising women. For three consecutive menstrual cycles, 25 subjects collected daily urine for the analysis of estrone conjugates (E1C), pregnanediol 3-glucuronide (PdG) [both adjusted for creatinine] and luteinizing hormone. Blood was collected on a single day during the early follicular phase (days 2–5) of each menstrual cycle for analysis of total triiodothyronine (T3) and leptin. Subject menstrual cycles were categorized into the following groups: (1) sedentary, consistently ovulatory (SedOvul, n = 24); (2) exercising, consistently ovulatory (ExOvul, n = 9); (3) exercising, inconsistent menstrual status, (ExIncon, n = 28); and (4) exercising, consistently luteal phase deficient (ExLPD, n = 12). All data were analyzed via a one-way ANOVA. Sedentary (n = 8) and exercising (n = 17) groups were similar in age (27.9 ± 1.3 years), weight (61.5 ± 3.9 kg), gynecological age (14.7 ± 1.3 years), and menstrual cycle length (28.6 ± 1.0 days). The ExLPD group had fewer (p < 0.05) days in the luteal phase (7.9 ± 0.8 days) compared to the SedOvul (13.2 ± 0.4 days), ExOvul (12.7 ± 0.5 days), and ExIncon (11.3 ± 0.4 days) groups. PdG excretion was significantly lower when assessed via peak PdG, mean luteal phase PdG and the sum of the 3-day mid-luteal PdG, in the ExLPD group compared to the SedOvul, ExOvul, and ExIncon groups. Serum total T3 was suppressed (p < 0.05) in the ExIncon (105.3 ± 3.3 ng/dL) and ExLPD (102.6 ± 5.2 ng/dL) groups compared to the SedOvul (144.8 ± 7.5 ng/dL) and ExOvul (132.4 ± 8.9 ng/dL) groups. Mean circulating serum leptin was significantly lower in the ExOvul, ExIncon and ExLPD groups (5.6 ± 0.6, 5.0 ± 0.4, and 4.9 ± 0.7 ng/mL, respectively) when compared to the SedOvul group (14.2 ± 1.7). These data demonstrate that serum leptin levels are significantly lower in exercising women independent of menstrual cycle status. Total T3 is significantly lower in exercising women with luteal phase deficient menstrual cycles independent of menstrual cycle consistency. The observation of suppressed T3 and leptin in exercising women with LPD is similar to observations in amenorrheic athletes and may represent a metabolic adaptation to altered energy status. ^

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