Volledig artikel- publicatie in Journaal American Association of Clinical Endocrinologists (AACE)
ENDOCRINE PRACTICE Rapid Electronic Article in Press
DOI:10.4158/EP171776.OR
© 2017 AACE.
FT3 IS HIGHER IN MALES THAN IN FEMALES AND DECREASES OVER THE LIFESPAN
Running title: Thyroid and age
From:
1 Department of Pediatrics, Shaare-Zedek Medical Center, and Pediatric Specialist Clinics, Clalit Health services, Jerusalem, Israel;
2 Department of Obstetrics and Gynecology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel;
3 Medical Data Unit, Clalit Health services, Jerusalem, Israel;
4 School of Medicine, Technion , Haifa, Israel;
5 Department of Pediatrics and Pediatric Endocrine Unit, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
Abstract
Objective:
Normal changes in Free triiodothyronine (FT3), Free thyroxine (FT4) and thyroid stimulating hormone (TSH) levels over the lifespan and differences between genders are not well documented, mainly because even the largest-scale studies available include relatively small cohorts. The aim of this study was to define age-related trends including gender differences based on reliable data.
Methods:
A large database including serum thyroid tests drawn in community clinics was studied. Free T3 (FT3), free T4 (FT4) and TSH levels from 527,564 sera taken from patients age 1 year or greater were included. After highly extensive exclusion criteria applied in order to remove all samples that may have been taken from unhealthy people, 27,940 samples remained. These were stratified by decades of age and by gender.
Results:
FT3 decreases throughout life, significantly more so among females, with equalization between genders in the elderly. FT4 declines, to a lesser extent, also more among females than among males. Among the extreme elderly, females have higher levels of FT4. In contrast, TSH declines until age 50 years and then increases slightly among both genders.
Conclusion:
This study provides reliable data regarding trends in hormonal levels by age and gender with the major finding being higher FT3 in males throughout life except in the very young and very old. These results have important implications for diagnosis and therapy of thyroid conditions.
Discussion
In this report we have shown trends for thyroid associated hormones over the entire lifespan
including separate data for males and females. The trend for FT3 in our large cohort and the
difference between the genders is similar to that previously reported by Kumari et al but the
graph is smoother, eliminating the increased level occurring at age 51-60 mentioned in the introduction (1).
The lower levels of FT3 throughout life among females may be due to testosterone levels in males that affect the peripheral (type 1) deiodinase with no similar effect on pituitary (type 2) deiodinase as shown among rats (7).
Recently this effect has beencorroborated by a report of the effect of testosterone upon female to male transgender patients (8). Among these subjects there are relatively higher levels of FT3 but similar levels of TSH compared to the hormonal levels prior to their gender change (8).
The increase in FT4 levels in females is probably a mirror effect of the reduction in FT3 since most T3 production in humans is from extrathyroidal deiodination of T4 (9). An interesting finding in our study is equalization of FT3 between genders in the over 80 age group. This age-group also comprises a much smaller number of males than females (see figure 1). One may speculate, that males with the higher FT3 did not survive into this age group as lower FT3 levels have been shown to be associated with longevity (10-12).
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Legend to figure 1 -
Flow chart for exclusions
Legend to figure 2 :
Thyroid function tests by age. Note that for all age groups differences between the genders
are significant except where “NS” (not significant) is noted
Table 1.
Regression analysis of dependence - variables associated with FT3
Link:
http://journals.aace.com/doi/pdf/10.4158/EP171776.OR
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