Thyroid Disease, Osteoporosis, and Calcium

Medical Author: Ruchi Mathur, MD
Medical Editor: William C. Shiel, Jr., MD, FACP, FACR

A very interesting patient came into my office last month. She was a fair, slender woman of Northern European background. In her mid 40's, she had already broken several bones (two of her wrist and one of her leg). Her primary doctor was appropriately concerned and had her evaluated with a bone density scan, which showed significant osteoporosis. Although she was slight and Caucasian (both risk factors for osteoporosis), there was no significant family history of fractures of which she was aware.

While the initial referral of this patient was for management of her bone disease, we started talking about her general health. She complained of extreme fatigue, unintentional weight loss, and a sense of heat intolerance. Her bowels were often loose and she had trouble sleeping. She was taking thyroid hormone replacement medication because she had had her thyroid removed years ago for a goiter. Because of an awareness of the association between excessive thyroid hormone and osteoporosis, I checked this patient's thyroid function. As I suspected, she was hyperthyroid due to taking an excessive amount of thyroid medication.

Thyroid disease falls into 2 major functional categories; conditions that produce too little thyroid hormone (hypothyroidism) and conditions that produce too much thyroid hormone (hyperthyroidism). In general, excessive replacement of thyroid hormone in medications can also result in signs and symptoms of hyperthyroidism. One of the problems that occurs when the thyroid is too active, or when too much thyroid hormone medication is given, is bone loss from osteoporosis.

Osteoporosis is the thinning of bone mass (decrease in bone density), which leads to fragile bones that can break more easily. There are a number of contributing factors for osteoporosis, including heredity, the amount of peak bone mass acquired during youth, and factors that contribute to an increased breakdown of bone and/or a decrease in the formation of new bone. Hyperthyroidism is associated with an increased excretion of calcium and phosphorous in the urine and stool, which results in a loss of bone mineral. This loss is documented by the measurement of bone density (densitometry) and leads to an increased risk of broken bones (fractures). If the hyperthyroidism is treated early, bone loss can be minimized. In the same manner, excessive amounts of thyroid hormone replacement medication can also result in bone loss.

In addition to osteoporosis, hyperthyroidism can cause blood calcium levels to rise (hypercalcemia) by as much as 25%. Occasionally, this may be severe enough to cause stomach upset, excessive urination, and impaired kidney function.

What do you need to know?

If you are on thyroid replacement medication, it is important to have your thyroid blood levels checked regularly to ensure that the appropriate amount of medication is taken. If you have a history of hyperthyroidism and are concerned that you may have osteoporosis, discuss the role of a bone density scan with your doctor. The level of calcium in the blood can easily be determined through a routine blood test.

If you have osteoporosis, there are many medications on the market that help to prevent further bone loss and can actually help to rebuild bone mass. Your doctor can guide you through the choices available. The main thing to remember is that prevention is the ideal course of action to fight osteoporosis. Weight-bearing exercises, a good diet, and calcium intake of about 1500 mg a day go a long way in helping your bones, regardless of whether you have or have had hyperthyroidism.

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