Two studies evaluated the effects of Tai Chi practice on the endocrine or immune systems. A cross-sectional Chinese study of 98 elderly men reported that 10 years of Tai Chi practice might widely affect endocrine function, including the pituitary-thyroid system and the pituitary-gonad system, and may strengthen pituitary metabolic reaction among elderly men. The conclusion of this study is questionable because cross-sectional studies are not designed to evaluate causality.