LOW THYROTROPIN LEVELS ARE NOT ASSOCIATED WITH BONE LOSS IN OLDER WOMEN - A PROSPECTIVE-STUDY

The relationship between excess thyroid hormone and bone loss is contr oversial. To determine whether low TSH levels, indicating excessive th yroid hormone, are associated with low bone mass or accelerated bone l oss in older women, we performed a prospective cohort study of 458 wom en over age 65 yr participating in the multicenter Study of Osteoporot ic Fractures. Three hundred and twenty-three women were randomly selec ted from the entire cohort of 9704; an additional 135 randomly selecte d thyroid hormone users were studied. Medical history, medication use, and calcaneal bone mineral density (BMD) were assessed at the baselin e visit. Serum was collected and stored at -190 C. Hip and spine BMD w ere measured approximately 2 yr later, and follow-up calcaneal and hip BMD measurements were obtained after mean follow-up periods of 5.7 an d 3.5 yr, respectively. TSH levels were determined in baseline serum s amples using a third generation chemiluminescent assay. After adjustme nt for age, weight, previous hyperthyroidism, and use of estrogen, bon e loss over 4-6 yr was similar in women with low, normal, or high TSH. For example, femoral neck bone loss was -0.3%/yr (95% confidence inte rval, -0.8%, 0.3%) among women with low TSH (less than or equal to 0.1 mU/L) and -0.5%/yr (95% confidence interval, -0.7%, -0.3%) in those w ith normal TSH (0.1-5.5 mU/L). There were no statistically significant differences in baseline bone mass of the calcaneus, spine, or femoral neck or trochanteric hip subregions. Baseline total hip BMD was 6% lo wer (P = 0.01) in women with low TSH. Similar results were obtained in analyses confined to women not taking estrogens. We found no consiste nt evidence that low TSH, a sensitive biochemical marker of excess thy roid hormone, was associated with low BMD or accelerated bone loss in older ambulatory women.