Posted by Phillipa on November 7, 2011, at 18:40:49
Seems weight loss also changes thyroid levels especially T3 levels. Need some interpretation.Does this mean you must be obese to have changes in T3 levels? Thanks Phillipa
Medscape Medical News from the:
American Thyroid Association (ATA) 81st Annual MeetingThis coverage is not sanctioned by, nor a part of, the American Thyroid Association.
From Medscape Medical News
Changes in T3 Levels Seen With Weight Loss in Obese
Nancy A. MelvilleAuthors and Disclosures
November 4, 2011 (Indian Wells, California) Obese people who undergo controlled weight loss show sustained changes in thyroid hormone triiodothyronine (T3) levels; however, the effects on central thyroid homeostasis are otherwise marginal, according to research presented here at the American Thyroid Association 81st Annual Meeting.
Thyroid hormone plays an important role in the regulation of the body's substrate metabolism and resting energy expenditure. In sedentary obese people, resting energy expenditure can account for as much as 85% of the body's total energy expenditure.
However, data on the effects of prolonged weight loss on thyroid homeostasis are limited, said lead author Ritesh Agnihothri, MD, from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), in Bethesda, Maryland.
"Most of the data are cross-sectional, and very little information is available on progressive changes as individuals lose weight," Dr. Agnihothri explained.
In evaluating how weight loss through dietary intervention affects thyroid homeostasis, Dr. Agnihothri and his colleagues from the NIDDK evaluated subjects enrolled in an ongoing study at the National Institutes of Health involving overweight and normal-weight subjects.
The researchers compared 47 overweight subjects (15 males and 32 females) with an average body mass index (BMI) of 34.12 kg/m² with 32 control subjects (19 males and 13 females) with an average BMI of 21.9 kg/m².
The weight-loss intervention involved an individualized calorie-restricted diet designed to achieve a 5% to 10% weight loss over the course of the 1-year intervention. Patients were placed on diets that had a 500 to 1000 calorie/day deficit, and were encouraged to increase physical activity.
All of the subjects were healthy; exclusionary criteria included cardiovascular disease, thyroid dysfunction, and a history of diabetes.
Measurements were performed at baseline, 6 weeks, and at 3, 6, 9, and 12 months. When Dr. Agnihothri presented the findings, 28 subjects had completed the study, 5 had completed 5 follow-up visits, 8 had completed 4 follow-up visits, and 7 had completed 3 follow-up visits.
Over the 12-month intervention, mean BMI dropped from 34 to 31.5 kg/m², with an average weight loss of 7 kg. "The patients who lost the greatest body mass were the ones who also saw the greatest drop in T3 levels," Dr. Agnihothri said.
Baseline T3 levels correlated with fat mass in overweight and control subjects (r² = 0.073; P < .02); however, a decrease in T3 levels (11.14 ± 19.7 ng/dL) was observed over the study period in the weight-loss group. The decrease in T3 levels correlated significantly with the level of weight loss (r² = 0.114; P < .0001).
Baseline thyroid-stimulating hormone (TSH) levels correlated with fat mass, but there was no correlation with free thyroxine (T4). At the end of the 12-month intervention, the TSH correlation with fat mass was no longer observed. Free T4 levels showed "marginal but significant" changes over the year, Dr. Agnihothri said.
"Interestingly, the correlation between resting energy expenditure and fat mass became even stronger after the intervention period," he reported.
The findings highlight the effect of weight loss on thyroid levels, Dr. Agnihothri said.
Leptin levels also declined with weight loss, as expected. "What we saw in the controlled weight-loss intervention was a trend toward a shift in the pituitarythyroid axis, which is consistent with a decrease in leptin."
"The data suggest that these changes are due, in part, to the changes in the pattern of peripheral conversion of thyroid hormone, owing to the greater changes in T3 vs TSH levels, and a marginal change in free T4 levels."
According to coauthor Francesco S. Celi, MD, an endocrinologist at the NIDDK, who also moderated the session, the study provides a unique look at thyroid changes as they occur over the course of weight loss.
"The study is original because the volunteers were followed over a 1-year period as they lost weight using a moderately individualized low-calorie diet," said Dr. Celi.
"The data suggest that that the peripheral conversion of the main product of the thyroid gland, T4, to its active metabolite, T3, plays a role in the changes that were observed."
"A trend toward a decrease in free T4 and TSH was also observed, but the greater changes in T3 support the interpretation of the data."
The authors have disclosed no relevant financial relationships.
American Thyroid Association (ATA) 81st Annual Meeting: Abstract 94. Presented October 28, 2011.
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