Thyroid disorders frequently lead to osteoporosis. The reason for this is that both thyroid hormone and thyroid stimulating hormone (TSH) have their own, independent roles in bone metabolism. Both are essential for bone health, but in thyroid problems one or the other of these hormones will be enhanced or blocked to treat the thyroid condition.
The definitions of hypo- and hyperthyroidism are not intuitive, but they respond to laboratory values of TSH. Normal thyroid function is reflected by lab values for TSH between 0.4 and 10.. A TSH value over 10 indicates hypothyroidism. The reason a higher number indicates "low" thyroid function is that TSH production sometimes has to be increased to make the thyroid respond by releasing thyroid hormone. A TSH value of 4 or more but less than 10 may be considered subclinical hypothyroidism. This is "not quite hypo-" thyroidism. Sometimes doctors intervene in this thyroid problem, but there may be implications for bone health. Hyperthyroidism is recognized by low TSH values. In hyperthyroidism the thyroid is working so hard it does not need the pituitary gland to send thyroid stimulating hormone (TSH), so TSH values will be low. A typical TSH value in hyperthyroidism is 0.05. A TSH value of 0.1 to 0.4 is "not quite hyperthyroidism," or subclinical hyperthyroidism, and may or may not be treated.
With regard to bone health, thyroid treatment has consequences, but failure to treat also has consequences
- Hypothyroidism carries an increased risk of fracture. It is assumed that once hypothyroidism is diagnosed, it is treated with thyroid hormone replacement therapy. However, there is a two- to three-times greater risk of fractures even 10 years after thyroid hormone replacement is begun,
- Subclinical hypothyroidism is a condition in which TSH levels that are unusually high, but not so high that there would be a diagnosis of hypothyroidism. Typically, "subclinical" hypothyroidism is noted when TSH levels are between 4 and 10. There is clinical evidence that giving supplemental thyroid hormone to people diagnosed with “not quite hypothyroidism” improves bone turnover. There is also evidence that untreated subclinical hypothyroidism in men carries a 2.3-times greater risk of fractures after age 65.
- Subclinical hyperthyroidism is a condition in which thyroid hormone levels are abnormally high, but not so high that the patient is always given a drug to suppress TSH. (TSH is the hormone that stimulates the thyroid to produce thyroid hormone, T4, and it also has its own role in stimulating the growth of bone.) Two studies have found that untreated subclinical hyperthyroidism results in greater risk of fractures in women. There is decreased bone mineral density body-wide and in the hip and upper spine. And a study that followed men with untreated subclinical hyperthyroidism found a 5-fold greater risk of fractures of the hip compared to men who do not have thyroid issues. However, treating the thyroid problem doesn't make the risk of bone problems go away. When subclinical hyperthyroidism is treated as a precaution, however, fracture rates increase dramatically. In one study, when TSH was suppressed to a level below 0.05 mU/L, fracture rates went up 250 percent. In another study, when TSH was suppressed to a level below 0.01 0.05 mU/L, fracture rates went up 300 to 400 percent. Treating subclinical hyperthyroidism with TSH suppression clearly increases the risk of fracture.
- Hyperthyroidism, also known as thyrotoxicosis, carries an increased risk of fracture until it is treated. That risk factor becomes insignificant after treatment begins. The problem is that there has already been significant loss of bone strength before the thyroid issue is properly diagnosed.
3 things you can do to maintain bone health when you have thyroid disease
The bottom line for practical management of bone health in thyroid disease is this: If you have any kind of thyroid issue, even if it is “subclinical,” not serious enough to treat, chances are you are at elevated risk of osteoporosis. There are many issues of hormone management that simply have to be left to your endocrinologist. However, there are some things you can do on your own to maintain bone health when you have thyroid disease.
- Avoid "acidity." It simply isn't true that acid builds up in your body and leaches the minerals out of your bones, but the reality is close to the misconception. In order to keep acid from building up in your body, your kidneys use the amino acid glutamine and minerals from bone to keep your pH normal. There is a simple test to determine whether your kidneys are working overtime to avoid metabolic acidosis. If you use a test strip to take the pH of your first morning urine, and it reads 6.0 or lower, your kidneys probably are robbing your bones of minerals to keep the pH of your blood normal. When this happens, "deacidify" your diet. Eat less meat, cheese, and dairy. Eat more fruits and vegetables.
- Avoid excess salt. Your kidneys may send hormones that cause your bones to release 1 gram of calcium for every 4 grams of sodium you consume. Sodium, from salt, depletes calcium. This is OK if you are replacing the calcium, but your body can only absorb about 1,500 mg of calcium per day. People who eat lots of salted fish or salted meat simply cannot consume enough calcium-rich foods or take enough calcium supplements to keep up with the loss from eating too much salt.
- Be careful with soy. Eating soy products generally is associated with increased bone mineral density, but the isoflavones from soy can interfere with estrogen’s protective action in bone when thyroid hormone levels are low.