BACKGROUND
The main thyroid hormone secreted by the thyroid is thyroxine, also known as T4. T4 is converted to T3, the active thyroid hormone, outside of the thyroid in tissues where thyroid hormone acts. Conversion of T4 to T3 is tightly regulated. During severe illness, conversion of T4 to T3 is downregulated, leading to low T3 levels. This helps conserve energy for the body to fight the severe illness. This is called the “low T3 syndrome” and is often seen in patients admitted to the hospital. Fasting and/or starvation can also cause the low T3 syndrome, especially in patients admitted to the hospital. There are studies that show that nutritional support in the hospital can decrease the likelihood of developing the low T3 syndrome.

This study investigated the role of the low T3 syndrome on clinical outcomes and response to nutritional support in patients admitted in the hospital.

THE FULL ARTICLE TITLE
Müller NA et al 2023 Low T3 syndrome on admission and response to nutritional support in malnourished medical inpatients. J Clin Endocrinol Metab 108:e240– e248. PMID: 36546619.

SUMMARY OF THE STUDY
This is an analysis of the Effect of Early Nutritional Support on Frailty, Functional Outcomes, and Recovery of Malnourished Medical Inpatients Trial (EFFORT), a trial of nutritional support in eight Swiss medical centers. In this analysis, adult inpatients with available free serum T3 levels (FT3) from the time of admission were included. Those included were malnourished, defined as ≥3 points in the Nutritional Risk Screening 2002 (NRS-2002) score, and had an expected length of hospital stay of ≥4 days.

Patients were divided into 2 populations based on FT3 levels: normal FT3 and “low T3 syndrome,” defined as FT3 <3.2 pmol/L (lower reference limit). Mortality (as assessed at 30 days, 180 days, and 5 years) was the primary end point. One group of patients received personalized nutritional support, supervised by a dietitian who composed an individual nutritional plan within 48 hours after hospital admission nwhile the other group received usual hospital care.

Serum FT3 concentrations were available for 801 of 2028 patients (39.5%). The average age of the 801 patients was 73.3 years, and 46.7% were female. Of these 801 patients, 492 (61.4%) had low T3 syndrome. Compared to those with normal FT3 levels, the patients with low T3 syndrome were older (71.5 years vs. 74.5 years) and had higher nutritional risk. Low T3 syndrome was associated with higher mortality at 30 days (~97% increased risk), 180 days (~39% increased risk) and 5 years (~26% increased risk). As compared with the usual hospital diet, the nutritional support intervention lowered mortality in the group of patients with low T3 syndrome by ~18%, althought this did not reach statistical significance.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study confirmed that inpatients with malnutrition that also have the low T3 syndrome are at increased risk of death. Further, these data suggest that nutritional support interventions can decrease the risk of death in these patients.

— Alan P. Farwell, MD

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