To study the relationship between TSH and forearm bone mineral density (BMD) in a general female population.

Cross-sectional, population-based study.

In a substudy of the Nord-Trøndelag Health Study 1995–1997 (HUNT 2), 5778 women without and 944 with self-reported thyroid disease aged ≥40 years had their serum TSH and distal and ultra-distal forearm BMD measured. In range-based categories of TSH, excluding women with previous thyroid disease, a general linear model was used to calculate adjusted mean BMD, and a logistic regression model to compute adjusted odds ratio (OR) for osteopenia and osteoporosis. Corresponding models were used to compare BMD in women with self-reported hypothyroidism or hyperthyroidism to euthyroid women.

In women without self-reported thyroid disease, those with TSH <0.5 mU/l had 10.7 mg/cm² (95% confidence interval (CI) 0.2–21.1) lower distal and 9.1 mg/cm² (95% CI −0.7–18.9) lower ultra-distal BMD than women in the reference category (TSH 0.50–1.49 mU/l). No differences were found between the categories with TSH ≥0.50 mU/l. Compared to self-reported euthyroid women, self-reported hyperthyroid women had increased odds for osteoporosis both distally (OR 1.35, 95% CI 1.00–1.82) and ultra-distally (OR 1.48, 95% CI 1.10–1.99).

Women with the lowest TSH (<0.5 mU/l) had lower forearm BMD than the reference category. No differences were observed between the TSH categories ≥0.50 mU/l. The prevalence of osteoporosis was higher in women who reported hyperthyroidism than in women without self-reported thyroid disease.