Heavy smokers have been shown to have substantial decreases in two thyroid hormones, T-3 (triiodothyronine) and T-4 (serum thyroxine). Several constituents of cigarette smoke are known to have antithyroid activity. Thyroid hormone level changes may have a profound effect on overall metabolism, as well as androgenic and estrogenic steroid activity. Light and moderate smokers demonstrated a milder decrease in thyroid hormone levels. (Archives of Internal Medicine 144:501-503, March, 1984) Copyright 1985 Phylis Austin
