Table of Contents
Did you know your bones are constantly rebuilding themselves? This amazing process, called bone remodeling, works around the clock to keep your skeleton strong and healthy. When everything’s working properly, your bones can handle everyday stress and recover from injuries without any special treatment.
In this post, we’ll explore four key topics: how the bone remodeling cycle works, what can throw this natural process off balance, what causes bone loss, and what you can do to help keep your bones in top shape.
To help us understand this better, I spoke with Dr. Theresa Guise from the MD Anderson Cancer Center in Houston. As a professor in the Department of Endocrine Neoplasia and Hormonal Disorders, she’s an expert in skeletal health.
What is Bone Remodeling?
Inside each bone lies a complex network of cells and essential components known as the bone microenvironment. This specialized environment serves as the foundation for bone remodeling, the natural process of bone formation and bone resorption that keeps our bones healthy and strong. In the next section, we will discuss the bone microenvironment (and specifically each of these bone cells) in detail.
How Osteoblasts and Osteoclasts Remodel Bone
The process of bone remodeling relies on three specialized cell types, each performing distinct but interconnected roles in maintaining bone health. Here’s how each type functions:
Osteoclasts: The Cells That Remove Bone
Osteoclasts are large cells that originate in the bone marrow. Their primary function is bone resorption, the process of breaking down and removing old or damaged bone tissue. While this may sound destructive, osteoclasts play an essential role in bone health. They not only clear away old bone tissue but also stimulate bone-forming activity and help maintain a balanced remodeling process.
Osteoblasts: The Bone Formation Cells
Osteoblasts are responsible for bone formation, the process of creating new bone tissue. These cells develop from mesenchymal stem cells and typically remain active for about two weeks. During their lifecycle, some osteoblasts take on a unique role: instead of dying off, they embed themselves within the bone matrix they’ve created. These embedded cells then release enzymes that help maintain healthy bone tissue and transform into a third cell type called osteocytes.
Osteocytes: Cells That Manage The Regulation of Bone
Osteocytes function as the bone’s monitoring system. They manage bone formation and bone resorption. These long-lived cells can survive for up to 25 years within the bone matrix. Their primary role is to detect microscopic damage and stress in bone tissue. Upon detecting these changes, osteocytes send signals to both osteoclasts and osteoblasts, coordinating their activities to maintain proper bone structure and strength.
The Bone Matrix
The bone microenvironment also includes the mineralized bone matrix – the hard outer portion of bone that gives bone its strength. This matrix is built primarily from type 1 collagen, a special protein that forms strong fibers. Beyond providing structural support, the bone matrix serves another vital function: it acts as a storage depot for growth factors, which are important proteins that help maintain bone health.
The Bone Resorption and Formation Process
Your bones are continuously renewing themselves through a remarkable process that involves bone formation and bone resorption. Every time you move, jump, or make sudden movements, you create tiny stress points in your bones that can develop into microscopic cracks, called microfractures.
Bone Resorption
As we mentioned above, special cells called osteocytes act as the bone’s surveillance system and regulate bone formation and bone resorption. They detect stress points and locate these microfractures in your bones. When damage is found, at a remodeling site osteocytes signal another type of cell, called osteoclasts, to remove the damaged bone tissue.
Bone Formation
After the osteoclasts (that originate from your bone marrow) finish removing damaged bone, they signal yet another type of bone cell, called osteoblasts, to begin their work. These cells arrive at the site and build new, healthy bone tissue to replace what was removed.
This continuous cycle of removal and rebuilding keeps your entire skeleton healthy and strong. The complete process takes about 120 days and occurs simultaneously throughout all parts of your skeleton.
Growth Phase and Bone Remodeling
Your bones are living, changing parts of your body that grow and transform throughout your life. Let’s look at how they change as you age.
From birth until about age 18, your long bones (like those in your arms and legs) gradually get longer. This growth doesn’t happen at a steady pace – sometimes it speeds up, like during growth spurts, and other times it slows down.
Osteoblasts make and lay down bone while the osteoclasts break bone down. The two cell types work in concert.
Peak Bone Mass
Your bones also get wider and their walls grow thicker until you’re about 30 years old when you achieve your peak bone mass. Think of it like a tree trunk getting thicker over time. At the same time, your bones are becoming denser as they pack in more minerals, especially calcium. This process peaks when you’re in your late twenties to early thirties.
How Adulthood Affects Bone Remodeling
While your bones stop getting longer by your early adult years, they never completely stop changing. Think of it like a tree – even though it might reach its full height, its trunk can still get thicker over time.
Throughout your entire life, your bones continue to adapt their shape and structure based on how you use them – like how exercise can make them stronger or how lack of activity can make them weaker. After that peak, bone density naturally starts to decrease, especially in women after menopause. [1]
How Mechanical Stress Impacts Bone Remodeling
When you engage in strength training, your muscles contract against the weight you’re lifting. All skeletal muscles are connected to your bones, either directly or through tendons. Each muscle contraction sends a mechanical signal to your bones that triggers two responses: it activates bone-building cells (osteoblasts) while reducing the activity of bone-removing cells (osteoclasts).
This physical stress also stimulates special cells called mesenchymal stem cells. These remarkable cells can develop into different types of tissue, including muscle, bone, cartilage, and ligaments. They respond particularly well to physical movement and mechanical forces. [2]
As we age, two significant changes occur: we naturally lose muscle mass, and the connections between our muscles and nerves become less efficient. This combination results in weaker muscles, which in turn leads to weaker bones.
However, there’s good news: your bones maintain their ability to strengthen themselves through physical activity at any age. This is why I strongly recommend staying active throughout your life. Whether you’re in your twenties or your sixties, your skeleton can still respond positively to regular exercise. [3]
Exercise Recommendations for Osteoporosis
Exercise is an essential ingredient to bone health. If you have osteoporosis, a therapeutic exercise needs to be part of your osteoporosis treatment program.
But what exercises should you do and which ones should you avoid? What exercises build bone and which ones reduce your chance of a fracture? Is Yoga good for your bones? Who should you trust when it comes to exercises for osteoporosis?
A great resource on exercise and osteoporosis is my free, seven day email course called Exercise Recommendations for Osteoporosis. After you provide your email address, you will receive seven consecutive online educational videos on bone health — one lesson each day. You can look at the videos at anytime and as often as you like.
I cover important topics related to osteoporosis exercise including:
- Can exercise reverse osteoporosis?
- Stop the stoop — how to avoid kyphosis and rounded shoulders.
- Key components of an osteoporosis exercise program.
- Key principles of bone building.
- Exercises you should avoid if you have osteoporosis.
- Yoga and osteoporosis — should you practice yoga if you have osteoporosis?
- Core strength and osteoporosis — why is core strength important if you have osteoporosis?
Enter your email address and I will start you on this free course. I do not SPAM or share your email address (or any information) with third parties. You can unsubscribe from my mail list at any time.
What Role Does Estrogen Play in Bone Remodeling?
Estrogen, an essential sex hormone, plays a crucial role in maintaining bone health by regulating how bones maintain and rebuild themselves. The most important form of estrogen for bone health, called estradiol ), works in harmony with three types of bone cells: the bone-building osteoblasts, the bone-removing osteoclasts, and the coordinating osteocytes.
During menopause, women experience a dramatic decrease in estrogen production. This decline disrupts normal bone maintenance by reducing the activity of osteoblasts, the cells responsible for building new bone tissue. When osteoblasts become less active, the delicate balance of bone renewal is disrupted, which can result in decreased bone density and strength.
While researchers have established estrogen’s importance in bone health, they continue to study the precise mechanisms behind this relationship. Current research suggests that estrogen may influence how certain stem cells develop into bone-building cells, though this theory requires further scientific verification.
Factors That Affect Bone Remodeling
Various factors can disrupt the natural process of bone remodeling. Hormonal changes significantly impact bone health, particularly in women. The decline in estrogen levels during menopause is a major factor that can disturb this delicate process.
Similarly, when women experience amenorrhea—the absence of one or more menstrual periods—their bone remodeling process can be disrupted. When bone remodeling becomes unbalanced (the bone resorption and bone formation processes become uncoupled), it may lead to decreased bone density and, potentially, osteoporosis.
Fortunately, many factors affecting bone health can be managed through lifestyle choices. Two critical areas where positive changes can make a significant difference are:
- Nutrition: The foods we eat, especially during our bone-building years, play a vital role in bone health. Poor nutritional choices during these crucial periods can have long-lasting effects on bone density.
- Physical Activity: Regular exercise is essential for maintaining healthy bones. An inactive lifestyle fails to provide the necessary stimulation for bone building. Without consistent physical activity, the bone remodeling process becomes less effective.
Bone Remodeling: Best Practices
While the hormonal changes of menopause and their effects on bone health are a natural part of aging for women, you can take proactive steps to maintain strong, healthy bones. A well-planned strategy can help keep your bone remodeling process functioning effectively.
Four key approaches can help protect your bone health:
- First, following a comprehensive osteoporosis exercise program helps maintain bone strength.
- Second, proper nutrition provides the essential building blocks your bones need to stay healthy.
- Third, low intensity vibration therapy can assist the bone remodeling process by stimulating mesenchymal stem cells (MSEs) to produce osteoblasts, the cells responsible for bone formation.
- For those whose bone density has decreased significantly, placing them at higher risk for fractures, medical professionals may recommend pharmaceutical treatments as a third line of defense.
Conclusion and Summary
Bone remodeling is a remarkable and continuous process (involving bone resorption and bone formation) that keeps our skeleton strong and healthy throughout our lives. This complex system involves three main types of cells—osteoclasts, osteoblasts, and osteocytes—working together in a carefully orchestrated cycle of removing damaged bone tissue and building new bone.
While this process occurs naturally, various factors can influence its effectiveness. Age-related diseases and many medications can have a significant impact on bone remodeling. However, understanding these changes allows us to take proactive steps to maintain our bone health.
Through regular physical activity, proper nutrition, and medical intervention when necessary, we can support our body’s natural bone remodeling process and maintain strong, healthy bones at any age.
Whether you’re in your twenties or your sixties, it’s never too late to start taking care of your skeletal health. By making informed lifestyle choices and working with healthcare professionals when needed, you can help ensure your bones remain strong and resilient for years to come.
Remember: your bones are constantly rebuilding themselves—give them the support they need to do their job effectively.
Margaret Martin
Further Readings
References
- Duren DL, Seselj M, Froehle AW, Nahhas RW, Sherwood RJ. Skeletal growth and the changing genetic landscape during childhood and adulthood. Am J Phys Anthropol. 2013 Jan;150(1):48-57. doi: 10.1002/ajpa.22183. PMID: 23283664; PMCID: PMC3539213.
- Rubin J, Styner M. The skeleton in a physical world. Exp Biol Med (Maywood). 2022 Dec;247(24):2213-2222. doi: 10.1177/15353702221113861. Epub 2022 Aug 19. PMID: 35983849; PMCID: PMC9899984.
- National Cancer Institute. SEER Training Modules. Anatomy & Physiology. Skeletal System. https://training.seer.cancer.gov/anatomy/skeletal/growth.htm
- Cheng CH, Chen LR, Chen KH. Osteoporosis Due to Hormone Imbalance: An Overview of the Effects of Estrogen Deficiency and Glucocorticoid Overuse on Bone Turnover. Int J Mol Sci. 2022 Jan 25;23(3):1376. doi: 10.3390/ijms23031376. PMID: 35163300; PMCID: PMC8836058.
Comments