Thyroid function and frailty in hospitalized older adults: the role of FT3 and FT3/FT4 ratio

Frailty is a crucial factor in managing older adults, given its strong predictive power for adverse health outcomes. Recent attention has focused on the relationship between frailty and thyroid function, particularly the so-called low T3 syndrome. However, the relationship between frailty and peripheral thyroid hormone metabolism remains under-investigated.

This cross-sectional study included 112 patients hospitalized in a single-centre geriatric unit. Data on thyroid function, cognitive performance (MMSE), handgrip strength, and comorbidities were collected. Frailty was assessed using the Rockwood Frailty Index (FI), with FI > 0.25 indicating frailty.

The study population (58 men, 54 women; median age 81 years) showed mild cognitive impairment (MMSE median 22.0; IQR 18.0-26.3) and reduced handgrip strength (13 kg; 10-20 kg). Median FI was 0.304 (0.196-0.383), and 62.5% of patients were frail. Frail patients were older and had significantly lower MMSE scores, weaker handgrip strength, and poorer renal function. FT3 levels and the FT3/FT4 ratio were significantly lower in frail than non-frail patients (P = 0.001 and P = 0.005, respectively). Increasing FT3/FT4 quartiles were associated with progressively lower FI values and frailty prevalence (P = 0.032 and P for trend = 0.042, respectively). In multivariable analysis, age (P = 0.017), MMSE (P < 0.001), and the FT3/FT4 ratio (P = 0.016) were independently associated with FI.

Lower FT3 levels and FT3/FT4 ratios were associated with greater frailty in hospitalized older adults. Prospective studies are warranted to validate their clinical utility as biomarkers of frailty.