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J Clin Endocrinol Metab. 2018 Nov 1;103(11):4163-4175. doi: 10.1210/jc.2018-01203.

Effects of Altering Levothyroxine Dose on Energy Expenditure and Body Composition in Subjects Treated With LT4.

Author information

1
Division of Endocrinology, Diabetes and Clinical Nutrition, Oregon Health & Science University, Portland, Oregon.
2
Family and Community Medicine Residency Program, Penn State Health St. Joseph, Reading, Pennsylvania.
3
Biostatistics and Design Program, OHSU-PSU School of Public Health, Oregon Health & Science University, Portland, Oregon.
4
Knight Cardiovascular Institute, Division of Endocrinology, Diabetes and Clinical Nutrition, Oregon Health & Science University, Portland, Oregon.

Abstract

Background:

It is unclear whether variations in thyroid status within or near the reference range affect energy expenditure, body mass, or body composition.

Methods:

138 subjects treated with levothyroxine (LT4) for hypothyroidism with normal TSH levels underwent measurement of total, resting, and physical activity energy expenditure; thermic effect of food; substrate oxidation; dietary intake; and body composition. They were assigned to receive an unchanged, higher, or lower LT4 dose in randomized, double-blind fashion, targeting one of three TSH ranges (0.34 to 2.50, 2.51 to 5.60, or 5.61 to 12.0 mU/L). The doses were adjusted every 6 weeks to achieve target TSH levels. Baseline measures were reassessed at 6 months.

Results:

At study end, the mean LT4 doses and TSH levels were 1.50 ± 0.07, 1.32 ± 0.07, and 0.78 ± 0.08 µg/kg (P < 0.001) and 1.85 ± 0.25, 3.93 ± 0.38, and 9.49 ± 0.80 mU/L (P < 0.001), respectively, in the three arms. No substantial metabolic differences in outcome were found among the three arms, although direct correlations were observed between decreases in thyroid status and decreases in resting energy expenditure for all subjects. The subjects could not ascertain how their LT4 dose had been adjusted but the preferred LT4 dose they perceived to be higher (P < 0.001).

Conclusions:

Altering LT4 doses in subjects with hypothyroidism to vary TSH levels in and near the reference range did not have major effects on energy expenditure or body composition. Subjects treated with LT4 preferred the perceived higher LT4 doses despite a lack of objective effect. Our data do not support adjusting LT4 doses in patients with hypothyroidism to achieve potential improvements in weight or body composition.

TRIAL REGISTRATION:

ClinicalTrials.gov NCT00565864.

PMID:
30165520
PMCID:
PMC6194808
[Available on 2019-11-01]
DOI:
10.1210/jc.2018-01203
[Indexed for MEDLINE]

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