Relationship Between Training Intensity and Volume and Hypothyroidism Among Female Runners

Abstract

Objective: 

To determine the effect of training intensity on thyroid function among female nonelite runners.

Design: 

Internet-based survey of medical history and training and racing habits of female runners.

Participants: 

A total of 1222 female runners aged ≥35 years.

Main Outcome Measures: 

Self-reported diagnosis of hypothyroidism and details of training and racing.

Results: 

Hypothyroidism was reported by 149 (12.2%). No characteristics of training intensity or duration, including average miles per week, training pace, or years of accumulated running were associated with thyroid dysfunction. Females who began running at or before age 10 were more likely to report a diagnosis of hypothyroidism versus those who began running at an older age (4.7% vs 1.5%, P = 0.018).

Conclusions: 

Our results do not support the concept of overtraining-related hypothyroidism among nonelite female distance runners although our data demonstrated a 3-fold increase in hypothyroidism among those who began a career at or before age 10. Further study is required to confirm and determine a possible mechanism of this association.