Free thyroxine and functional mobility, fitness, and fatigue in euthyroid older men and women in the Baltimore Longitudinal Study of Aging

Abstract

Background: Emerging evidence suggests that mildly down-regulated thyroid function in older persons may protect and/or reflect maintained health. Methods: Using observational data collected between January 2006 and March 2014 on a volunteer sample of 602 men and women aged 68-97 years with normal thyroid function participating in the Baltimore Longitudinal Study of Aging, this study examines the concurrent relationship between reported walking ability, usual and rapid gait speed, endurance walk performance, fatigability, and reported energy level with respect to free thyroxine (FT4) within the normal range (0.76-1.50 ng/dL) as a continuous variable and categorized as low (lower quartile), medium (interquartile), or high (upper quartile). Results: Adjusting for sex, age, race, height, weight, exercise and smoking, reported walking ability, usual and rapid gait speed, 400-m time, fatigability, and reported energy level were less favorable with increasing FT4 (p=.013 to