Thyroid hormone concentrations in a large scale community survey. Effect of age, sex, illness and medication

Abstract

Total thyroid hormone concentrations have been measured in the course of a large scale community survey to determine the distribution of these variables in the normal population and to assess the effect of age, sex, previously undetected thyroid disease and medication upon these parameters. 2779 subjects were studied. Serum T 4 concentrations were normally distributed. A progressive increase in T 4 levels with age was noted in the males, and a smaller increase in females which was concealed by the raised T 4 values secondary to oral contraceptive therapy in females under the age of 45. Serum T 3 levels were also normally distributed. There was a small reduction in T 3 with age in the males but this fall was not seen in the females. T 3 values were relatively higher in females under the age of 45 but this increase was not noted after exclusion of subjects taking an oral contraceptive. The changes in thyroid hormone concentrations with age are relatively minor (particularly with respect to T 3) in a randomly selected sample from an English town. It is suggested that the changes reported by other authors reflect the processes of selection used, and the high frequency of undetected thyroid disease, other illness and medication in hospital-based communities.