Thyroid status and brain circulation: The Rotterdam Study

[helvella]

Given how many here have reported issues which were, or could have been, mistaken for stroke or dementia, this paper seems of great relevance.

Thyroid status and brain circulation: The Rotterdam Study

Lana Fani, MD PhD, Oscar Roa Dueñas, MD MSc, Daniel Bos, MD PhD, Meike W Vernooij, MD PhD, Caroline C W Klaver, MD PhD, M Kamran Ikram, MD PhD, Robin Peeters, MD PhD, M Arfan Ikram, MD PhD, Layal Chaker, MD PhD

The Journal of Clinical Endocrinology & Metabolism, dgab744, doi.org/10.1210/clinem/dgab744

Published:11 October 2021

Abstract

Context

Whether thyroid dysfunction is related to altered brain circulation in the general population remains unknown.

Objective

We determined the association of thyroid hormones with different markers of brain circulation within community-dwelling elderly.

Design

Three subcohorts of the Rotterdam Study, starting in 1989, 2000 and 2006 respectively.

Setting

Population-based.

Patients or Other Participants

A total of 5,142 participants (mean age, 63.8 years; 55.4% women), underwent venapuncture to measure serum thyroid-stimulating hormone (TSH), free thyroxine (FT4).

Main Outcome Measures

Between 2005 and 2015, all participants underwent phase-contrast brain magnetic resonance imaging to assess global brain perfusion (mL of blood flow/100 mL of brain/min). Arteriolar retinal calibers were assessed using digitized images of stereoscopic fundus color transparencies in 3,105 participants as markers of microcirculation. We investigated associations of TSH, FT4 with brain circulation measures using (non-)linear regression models. Results. FT4 (in pmol/L) levels had an inverse u-shaped association with global brain perfusion, such that high and low levels of FT4 were associated with lower global brain perfusion compared to middle levels of FT4. The difference in global brain perfusion between high FT4 levels (25 pmol/L) and middle FT4 levels (FT4 = 15 pmol/L; P non-linearity = 0.002) was up to -2.44 mL (95% confidence interval (95%CI)= -4.31; -0.56). Similarly, higher and lower levels of FT4, compared with middle FT4 levels, were associated with arteriolar retinal vessels (mean difference up to -2.46 µm, 95%CI -4.98; 0.05 for lower FT4).

Conclusions

These results suggest that thyroid dysfunction could lead to brain diseases such as stroke or dementia through a suboptimal brain circulation that is potentially modifiable.

Thyroid, cerebral blood flow, brain perfusion, general population, cohort study, free thyroxine

PDF of full article but in accepted manuscript form (double-line spaced) currently available at link. Final paper might not be accessible.

academic.oup.com/jcem/advan...

[tattybogle]

interesting thanks .. and nice to be able to see the graphs while they are available . Raises another potential '?' over whether it really is OK to use over range fT4 to get enough fT3 / feel well .. or whether this practice is really not wise and we should insist on using less Levo and having adding a little T3 instead .

However .. this study is only including those without any thyroid disease / medication .. so a top end fT4 on Levo possibly doesn't translate to the same bodily effects as a high end fT4 without Levo ..... due to Levo's habit of giving a higher fT4 /lower fT3 for a given TSH.

( this is in addition to recent concerning thoughts about the role of natural T4 in cancer proliferation )