When it comes to bone health and bone density, hormones help prevent osteoporosis, a condition in which bones become weak and more susceptible to breaking.
Hormonal problems can be one of the causes of osteoporosis, so it is important to understand the connection between hormones and osteoporosis.
Bone production is affected by both testosterone and estrogen, so both men and women can experience bone loss as they age. Levels of both hormones drop with age, with the risk being higher in women.
Other hormonal imbalances, including thyroid or pituitary gland problems and lower hormone production connected with eating disorders, also can harm bone health.
So, what exactly are bones?
Bones are living, growing tissue.
Although they may appear solid, they are in fact a mix of hard and soft tissue. They are made up of different types of cells with different functions, have a rich blood supply, and are home to specialized immune cells.
Some bones, like the spine and hip, also contain active bone marrow – spongy tissue that makes red and white blood cells.
Our bones live in a constant state of change or remodeling – older bone is continuously being broken down while new bone is formed. Our overall health and lifestyle can affect this process.
There are 3 main types of bone cells that are involved in bone remodeling:
- Osteoblasts – these are cells that create new bone. They release proteins like collagen that form the bone matrix (3D scaffolding) and then release minerals (including calcium) that bind to this matrix. When bone surfaces are not undergoing formation or resorption, they become lined with old osteoblasts that have flattened. These are then called bone lining cells. Under certain conditions, the bone lining cells can return to become bone-forming osteoblasts again.
- Osteoclasts – these are cells that break down and resorb old or damaged bone. They do this by releasing enzymes at the bone surface which digests the bone matrix and frees calcium from the bone.
- Osteocytes – these cells can live for up to 25 years and make up most (90-95%) of the calcified bone. Osteocytes are surrounded by a mineralized bone matrix but have long branches (or extensions) that connect them to other bone cells. These extensions allow bones cells to transport molecules and signal each other, which can start the bone repair or bone remodeling process.
Maintaining healthy bones is a balancing act
A balance between bone formation and bone breakdown is important for maintaining bone mass and density. If this balance is not maintained, problems can occur that might affect the strength of your bones, and how easily they break. For example:
Too much bone breakdown without a corresponding amount of new bone being formed can lead to bone loss and osteoporosis. This is where bones lose density and strength and are easily broken.
Too much bone formation without a corresponding amount of breakdown is seen in a rare condition called osteosclerosis, where bones become harder and denser.
What hormones keep bone remodeling processes under control?
A number of hormones play key roles in keeping bone remodeling processes in check.
Parathyroid hormone (PTH): The main role of this hormone is to keep blood calcium levels stable. If calcium levels fall too low, the parathyroid glands release PTH.
This causes the bones to break down so that calcium can be released from the bones into the bloodstream. If this happens over a long period of time, the bones can become too weak, leading to osteopenia or osteoporosis.
Calcitonin: This hormone also acts to keep calcium levels stable but works in the opposite direction to the parathyroid hormone. If calcium levels in the blood get too high, calcitonin reduces bone breakdown by osteoclasts. This means more calcium stays in the bones to keep them strong.
Growth Hormone (GH): This hormone plays a key role in the growth of bones during childhood, but also maintains bone health in adulthood. Growth hormone stimulates osteoblast activity, promoting bone formation. GH deficiencies can lead to a gradual loss of bone density.
Vitamin D (or calcitriol): This hormone helps the body absorb calcium. If Vitamin D levels are low for a long time, calcium levels in the body can fall. This causes PTH release, which in turn causes the bones to break down to release their calcium.
Glucocorticoids: These hormones act on osteoblasts to reduce bone formation, as well as cause a period of increased bone breakdown.
The effect of these hormones is seen when taking high-dose, oral, or injected glucocorticoid medications, such as prednisolone, for a prolonged period.
Estrogen: The major effect of the loss of estrogen is an increase in bone
This is why the rapid fall in estrogen levels that occurs in the 5-10 years following menopause can cause significant bone loss in women.
Androgens: These male sex hormones are also important for keeping bones healthy. This mainly happens because some testosterone is naturally converted to estrogen, which protects bone health. Low testosterone levels can therefore also lead to increased bone loss.