New paper showing TSH is related to body composition in the elderly but not those below 60 years

[diogenes]

This downloadable paper in Nature Research relates TSH to body composition,

Obesity therefore has an effect on TSH levels.

Low serum TSH levels are associated with low values of fat‑free mass and body cell mass in the elderly

Till Ittermann1,4* , Marcello R. P. Markus2,4,5 , Martin Bahls2,4 , Stephan B. Felix2,4 , Antje Steveling6 , Matthias Nauck3,4 , Henry Völzke 1,4 & Marcus Dörr2,4

Previous studies on the association between thyroid function and body composition are conflicting and showed strong differences across age groups. Our aim was to clarify age‑specific associations of serum thyroid‑stimulating hormone (TSH) levels with markers of body composition including body mass index (BMI), waist circumference, fat mass (FM), fat‑free mass (FFM) and body cell mass (BCM). We used data from two independent population‑based cohorts within the framework of the Study of Health in Pomerania. The study population included 5656 individuals aged 20 to 90 years. Markers of body composition were measured by bioelectrical impedance analysis. Serum TSH levels were significantly positively associated with BMI (β = 0.16; 95% confidence interval [CI]: 0.06 to 0.27), waist circumference (β = 0.35; 95% CI: 0.08 to 0.62) and FM (β = 0.32; 95% CI: 0.12 to 0.52), but not with FFM and BCM. Interaction analysis revealed positive associations of serum TSH levels with BMI, waist circumference, FM, FFM and BCM in individuals older than 60 years, while no such associations were observed in younger individuals. We demonstrated that lower serum TSH levels were accompanied with lower values of BMI, waist circumference, FM, FFM, and BCM in the elderly, while no such associations were observed in younger individuals.

To understand effects of thyroid dysfunction on body composition, it is important to not just look at the global obesity marker BMI but also at specific markers of body composition including fat mass (FM), fat-free mass (FFM) and body cell mass (BCM). While there are many studies investigating associations of thyroid function with BMI, fewer studies researched potential associations of thyroid dysfunction with muscle or lean mass. In a cross-sectional, population-based study with 946 males aged 25 to 45 years no significant association between serum TSH levels and lean mass was observed

Institute for Community Medicine, University Medicine Greifswald, Greifswald, Germany. 2 Department of Internal Medicine B – Cardiology, Intensive Care, Pulmonary Medicine and Infectious Diseases, University Medicine Greifswald, Greifswald, Germany.3 Institute for Clinical Chemistry and Laboratory Medicine, University

Medicine Greifswald, Greifswald, Germany. 4 German Centre for Cardiovascular Research (DZHK), Greifswald, Germany. 5 DZD (German Center for Diabetes Research), Greifswald, Germany. 6 Department of Medicine A, University Medicine Greifswald, Greifswald, Germany. * email: till.ittermann@uni-greifswal

doi.org/10.1038/s41598-021-...

[PiggySue]

Very interesting. I note that it was a study of males, I wonder whether the results would be the same regardless of gender, particularly in younger individuals?

[diogenes Remembering in reply to PiggySue]

I would think so

[Beads in reply to PiggySue]

Was it though? The initial study was across 5656 people, with no gender specified, aged between 20 and 90. The smaller study of 946 younger (25-45) were all males. If the ages were spread equally then I’d expect more within the 25-45 age range.

[Beads]

Are they looking at cause or effect?If a higher BMI/fat composition is related to a higher TSH, I could have told them that without the study. We know that (usually) higher TSH equals lower thyroid hormones, equals lower metabolic rate, equals body mass increase.

Or are they saying that as we get older we put on weight, our body mass increases and causes our TSH to increase?

I need to get moving now or I’ll be sat in this chair for the rest of the day, will click through and read it properly later.

[diogenes Remembering in reply to Beads]

The main thing coming from this paper is that TSH does not mirror thyroid function, and the property of being obese means that it is a form of nonthyroidal illness, where the relationships between FT4, FT3 and TSH are altered. We call this a change in the "set point" for the individual.

[Musicmonkey in reply to diogenes]

How does this knowledge help us ? Is this a chicken and egg situation? What comes first, hypothyroidism or obesity? Obesity or hypothyroidism? Or can it be either?

[diogenes Remembering in reply to Musicmonkey]

Obesity in most situations. There are a lot more obese people than hypothyroid ones.