Hypothyroidism & Bone Density

The scientific consensus is that untreated hypothyroidism causes an abnormally increased bone density coupled with poor bone quality. Treatment with thyroid hormone (T4), however, may further impair bone quality and lead to an increased risk of fracture.

The pituitary gland naturally produces thyroid stimulating hormone (TSH) in response to low levels of thyroid hormone in the body. Synthetic or natural T4 lowers the amount of TSH that alters bone metabolism and decreases bone density. Consequently, treatment with T4 inadvertently weakens bones—an effect that is controversial.

There is a difference between bone density and bone strength. Dense bone exhibits abnormalities in its micro-architecture and is weakened by those changes. Abnormal levels of thyroid hormone also have a deleterious effect upon bone strength. Weak bone is a combination of accumulated damage, as well as changes in micro-architecture, collagen quality, mineral crystal size and bone turnover.

Following an analysis of current research on hypothyroidism it would be reasonable to conclude that high or low levels of TSH are deleterious to normal bone metabolism. Laboratory ranges show a TSH range of 0.35 to 5.5 is normal, but these ranges are based upon a statistical analysis of blood samples. They do not necessarily represent a "healthy" or functional range for TSH that is closer to 1.8 to 3.0. Levels above or below this range may impair bone strength.