Is There A Connection Between The Thyroid And Bone Health?

The thyroid is a small gland in the front of the neck that usually lies along the windpipe. This gland is split into two joined lobes, resembling a butterfly shape. It has a range of important modulatory effects and can be tied to almost every process in the body. 

Functions of the thyroid

The thyroid functions to help regulate metabolism and other important bodily processes through the synthesis of thyroid hormones known as thyroxine (T4) and triiodothyronine (T3). 

These hormones are synthesized when the thyroid cells take iodine and tyrosine (an amino acid) and combine them together to make T4. This T4 is then converted into T3, which is the more active form. 

Thyroid function is regulated by the amount of circulating T3 and T4. When there is too much of either, the brain will change the level of thyroid stimulating hormone (TSH) to reduce the amount of T3 and T4 being produced. This stops the body from overproducing thyroid hormones. 

In the case of not enough thyroid hormones, the opposite occurs. The TSH level would increase in the bloodstream to stimulate the thyroid to create more T3 and T4 until their circulating levels are restored to normal. 

Once they have been released from the thyroid gland, T3 and T4 help to regulate metabolism. They do this by converting oxygen and calories into energy. This energy can then be used by the cell in the daily processes that help to keep us alive. 

Bone development 

The skeletal system is another major system in the body that is responsible for supporting life. This system is made up of four different cell types: chondrocytes, osteoblasts, osteocytes, and osteoclasts. 

Chondrocytes are responsible for forming cartilage and come from the first stages of human development. These cells are derived from mesenchyme, which is the middle layer of tissue in embryonic tissue organization. 

Osteoblasts and osteocytes are also from mesenchyme but have a different role to chondrocytes. Osteoblasts lay down new bone, and osteocytes help to regulate the formation of new bone and the resorption of old bone. Both chondrocytes and osteoblasts are responsive to thyroid hormones.

The last type of bone cell, osteoclasts, are from a different tissue to the others. This type of bone cell derives from cells of the adaptive immune system, and they are responsible for reabsorbing bone as it breaks down. Osteoclasts can also be sensitive to changes in thyroid hormones. 

The link between thyroid and bone development

Thyroid hormones are important — not only for skeletal development but also for all stages of life. They are responsible for creating linear growth during childhood and adolescence, as well as maintaining the bone mass and strength of adults. 

The thyroid gland is mainly responsible for secreting T4 and T3. These hormones can be transported by specific transport proteins all over the body, where they enter cells and become metabolized. 

Once metabolized, the products of T3 and T4 function as transcription factors, where they enter the nucleus of the cell (where all the genetic material is kept) and allow the transcription of some genes. 

Transcription is the first stage of gene expression in a cell. It is a multi-step process where the coded DNA is turned into a message that can exit the nucleus and interact with the rest of the cell to create proteins. 

Transcription needs to occur in order to control the gene expression of the cell. This allows the cell to be differentiated, which means having different functions while maintaining the same amount of genetic material. 

This transcription is partially regulated by the amount of thyroid hormone in the body, so thyroid function is extremely important to maintain regular bodily functioning. 

This is particularly important in bone tissues because thyroid hormones induce the expression of genes that are important in bone formation. 

Main signs and symptoms

There are two main forms of thyroid issues, although there are several different causes for each. 

Hyperthyroidism and hypothyroidism have different symptoms, which can help to tell them apart. 

Hypothyroidism

Hypothyroidism is an underactive thyroid condition. It can cause the following symptoms:

• Fatigue

• Cold sensitivity

• Weight gain

• Slow bowel movements or constipation

• Depression

• Slower movements and lethargic thoughts

• Muscle aches, cramps, or weakness

• Dried and scaly skin

• Brittle hair and nails

• Loss of sex drive

• Pain, numbness, or tingling in the hands and fingers

• Irregular or heavy periods

When hypothyroidism is left untreated, it can sometimes progress further to show the symptoms below. However, it is important to note that this is very unusual, as most cases of hypothyroidism are diagnosed well before these symptoms appear. 

• A low-pitched and hoarse voice

• Puffy or swollen face

• Thinning eyebrows

• Slow heart rate

• Hearing loss

• Anemia

Hyperthyroidism

The other kind of thyroid disease, hyperthyroidism, is where you have an overactive thyroid that produces too much thyroid hormone. 

Hyperthyroidism has the following symptoms:

• Nervousness or anxiety

• Hyperactivity (restlessness or fidgeting)

• Mood swings

• Difficulty sleeping

• Fatigue 

• Sensitive to heat

• Muscle weakness

• Diarrhea

• Frequent urination

• Persistent thirst

• Itchiness

• Lack of sex drive

In addition to these symptoms, an overactive thyroid can also present physically as signs. These signs can include:

• Swelling in the neck

• Rapid heart rate 

• Tremor

• Warm skin with excessive sweating

• Red palms

• Loose nails

• Hives

• Patchy or thinning hair loss

• Weight loss

• Eye problems

Prevalence

If the above symptoms seem like they could fit with what you’re experiencing, then it’s best to see a doctor. Thyroid disease may seem like a scary diagnosis, but it is actually more common than you think. 

It is estimated that around 20 million Americans have a thyroid disease and that up to 60% of those people are unaware of their conditions. Thyroid diseases are especially common in women and can be 5–8 times more frequently found in women than in men. One in 8 women will develop a thyroid disorder over her lifetime.¹

Risk factors

There are numerous risk factors for developing a thyroid disorder. 

One study attempted to understand the risk factors for women with autoimmune thyroid diseases (discussed in more detail later). 

They found that there were both genetic and environmental causes for thyroid conditions. In short, you are more likely to have thyroid disorders if someone else in your family has had them, but there are also environmental causes that can make you more likely to develop thyroid disease. 

Factors that increase the risk  

Some of the factors found to be significant in increasing the risk of thyroid disorders are:

• Presence of thyroid peroxidase (TPO) antibodies 

• Female gender

• Smoking

• Obesity

• Pregnancy

• High blood pressure

• Family history of thyroid disease

• Excessive iodine consumption 

All of these factors are still being investigated, and there are a host of other immune factors that are also involved.

Thyroid disorder causes

Earlier, we explained what hyperthyroidism and hypothyroidism are. Essentially, the thyroid can either overproduce (hyperthyroidism) or underproduce (hypothyroidism) T4 and T3 hormones.

Overactive thyroid (hyperthyroidism)

The most common cause of hyperthyroidism is Graves' disease. This condition affects roughly three-quarters of those with hyperthyroidism, so if you have an overactive thyroid, it's a fairly good bet you could have Graves' disease. 

Graves' disease is an autoimmune condition, meaning that it is caused by your own immune system attacking itself by mistake. In this case, the immune response causes the thyroid gland to be overstimulated. 

It isn’t known what causes Grave’s disease, but it can be inherited. It is also more likely to be associated with people who smoke. 

Another potential cause of hyperthyroidism is a thyroid nodule. This is a small growth or lump that can sometimes contain thyroid tissue. Essentially, the lump functions as an extra bit of thyroid and can create excess thyroid hormones in the body. 

Another probable cause of hyperthyroidism is an overabundance of iodine. Since iodine is used to create thyroid hormone, when we ingest too much iodine (for instance, by taking certain medicines), we can accidentally overdose on iodine. 

Hyperthyroidism can also be caused by excessive intake of thyroid hormones and several other medications. Thyroiditis, the inflammation of the thyroid gland, is another potential cause. 

Underactive thyroid (hypothyroidism)

With an underactive thyroid, the issue is that not enough thyroid hormones are being synthesized. This is generally caused by Hashimoto’s disease, an autoimmune condition where the immune system attacks and damages the thyroid gland. 

It isn’t known what causes Hashimoto’s disease, but it can be inherited and is more common in people with other autoimmune disorders (such as type 1 diabetes). 

Another cause of hypothyroidism is damage as a complication of treatment, which can include prior treatment for an overactive thyroid or when someone has thyroid cancer. 

In addition, if you have a lack of iodine in your diet, you are more likely to develop hypothyroidism. This is because iodine is a required ingredient for the synthesis of thyroid hormones, so when it isn’t available in the diet, the hormones can’t be created, and you get symptoms of hypothyroidism. However, this is uncommon due to iodine dietary supplements. 

Role of thyroid in skeletal development and bone maintenance 

Thyroid hormones are essential for the maintenance of skeletal development and bone turnover. This is because of the way the skeleton develops to form bone. 

Most of the bones in the skeleton are formed and maintained through a process known as endochondral ossification. This is a complicated term to describe the replacement of cartilage by bone tissue in the skeleton. 

This process is regulated by many hormones, including thyroid hormones, which are essential for skeletal maturation, bone turnover, and maintenance. 

An excessive amount of thyroid hormones can induce an increase in bone turnover and cause fractures. Too few thyroid hormones can cause a loss of bone mass. 

Thyroid disorders and bone mineral metabolism

Thyrotoxicosis and bone

Normal bone mineral homeostasis is controlled by parathyroid hormone (PTH), 1,25(OH)2D, and calcitonin. Thyroid hormones have a direct catabolic effect on bone mineral homeostasis, which can cause the bone minerals to be resorbed and then lost through the kidneys. 

Can thyroid problems affect bone density?

Thyrotoxicosis is a term that means excessive thyroid hormone activity and usually refers to hyperthyroidism. It is distinguished from hyperthyroidism because it specifically refers to the clinical state associated with high levels of thyroid hormone activity and not the actual level of thyroid hormone itself. 

In patients with thyrotoxicosis, loss of bone density can occur, although treatment can reverse this. Historical case studies show patients with multiple fractures to the ribs, which are so fragile they could easily be crushed between fingers.²

What effect does hypothyroidism have on bones?

Research has found links between hypothyroidism and bone problems.³

Recently, it has been discovered that thyroid hormones regulate remodeling cycles in bones, which can stimulate osteoclastic and osteoblastic activity. In hypothyroidism, bone turnover is reduced, and the time spent in the bone remodeling cycle is increased. 

In children, hypothyroidism can also cause delayed skeletal development and defective bone formation. 

Alterations in calcium homeostasis in hyperthyroidism

Some patients with hyperthyroidism can also have an increase in the free levels of calcium in their blood. However, more research is required to investigate hyperthyroidism-associated hypercalcemia. 

We know that hypercalcemia and hyperthyroidism are linked because when we treat hyperthyroidism, hypercalcemia resolves. 

Alteration in phosphorus homeostasis in hyperthyroidism

Phosphorus is another important bone mineral that is also believed to be linked to levels of thyroid hormones in the body. Most studies that have investigated phosphorus have noticed an increase in serum phosphorus at the same time as hyperthyroidism. However, a few studies haven’t observed this increase. 

Hyperphosphatemia (the increase in phosphorus in the blood) has been explained by the increase in tissue catabolism that occurs in hyperthyroidism from bone reabsorption. However, the phosphorus isn’t excreted like calcium and is instead put into a plasma pool. 

Thyroid disorders and osteoporosis

Can an overactive thyroid cause osteoporosis? 

If left untreated, severe hyperthyroidism can lead to osteoporosis, which is the lack of bone density that causes small holes and fragility. It is usually painless until the fragility causes fractures. 

Hyperthyroidism can lead to the release of minerals essential for bone formation and maintenance, such as calcium, from the bone into the blood. This leads to osteoporosis. 

How are these diagnosed?

Thyroid levels can be diagnosed through a simple blood test. This test will measure the level of thyroid stimulating hormone (TSH) in the blood.

 If TSH is abnormal, the doctor will generally then test for T3 and T4. 

High TSH with low T3 and T4 indicates hypothyroidism, while low TSH with high T3 and T4 indicates hyperthyroidism.

Sometimes, TSH is abnormal, but the thyroid hormones are still within a normal range. This can suggest subclinical hypothyroidism (when TSH is high) or subclinical hyperthyroidism (when TSH is low).

Doctors can also test for osteoporosis if you have had a prolonged experience of hyperthyroidism. This test is done through dual-energy x-ray absorptiometry, which measures bone density and is often done at the hip and spine. 

Common thyroid medicines that affect the skeleton

What to know about taking thyroid medicine

It can sometimes take time to get the right dosage of thyroid medications, so if you are being treated for hypothyroidism with levothyroxine, you may accidentally be put on too high of a dose, leading to hyperthyroidism. 

The dosage will often depend on your weight, and most doctors will start you off with a low dose to ensure that you don’t get the mimicked effects of hyperthyroidism. Unfortunately, everyone responds differently to thyroid medications, so it is impossible to say you will never get these complications. 

Some thyroid medicines can affect the skeleton. This includes any thyroid medicines that cause hyperthyroidism, as it can lead to the complications talked about earlier.

Effect of thyroid hormone treatment on bone density

Some patients who take thyroid suppression medications do so because of thyroid cancer. In this case, they could take thyroxine (T4) to suppress the action of thyroid stimulating hormone. The rationale for this treatment is that TSH leads to cell proliferation, which would encourage tumor growth. 

The evidence on the effects of thyroid hormone treatment on bone density is mixed. Some research suggests that post-menopausal women taking suppressive doses of T4 may be at greater risk of bone loss and osteoporosis. Other studies have found that the risk of fractures actually reduces after thyroid hormone treatment.⁴ ⁵

What are the treatment options?

Treatment differs for hypothyroidism and hyperthyroidism. 

Hypothyroidism

Hypothyroidism is usually treated by taking thyroid hormone supplements, such as levothyroxine. Because this treatment can lead to hyperthyroidism if not managed correctly, it is essential that you take it as prescribed by your doctor and that you’re monitored closely to make sure the dose is safe and effective for you. 

Hyperthyroidism

Hyperthyroidism is a bit more complicated and has a few treatments. These include thioamides (medications to stop thyroid production), radioactive iodine treatment to destroy some thyroid cells and reduce the amount of thyroid hormones produced, or surgery to remove some of the thyroid and lower the amount of thyroid hormones produced. 

Your doctor will be able to work with an endocrinologist (hormone specialist) to come up with the best treatment plan for you. 

The lowdown

The thyroid gland is a small gland in the neck shaped like a butterfly. It is responsible for producing thyroid hormones T4 and T3, which are both essential for several life processes. In particular, they are able to change and stimulate bone production by working as transcription factors. 

When bone production is overstimulated by too much of the thyroid hormones (as in the case of hyperthyroidism), it can lead to osteoporosis. This is because the thyroid hormones inappropriately activate some of the bone cell types and create reabsorption of minerals essential for bone maintenance. 

These absorbed minerals are then lost through the kidney filtration system or kept in the plasma pool and are no longer available for bones. This causes weakened bones and loss of bone mass. 

Thyroid disorders are actually quite common and can be diagnosed through a blood test. In most cases, the treatment is relatively simple and safe, so it would be a good idea to see your doctor if you exhibit any signs of thyroid disorder.