The purpose of this presentation is to give the reader a better understanding of bone health. This is the first of a two part series on bone health, osteoporosis, exercise and cancer. In this first part, I provide a comprehensive understanding of bone health. Specifically, I discuss the six critical functions your bones fulfill, I describe types of bone, bone cells and remodelling of bone, the key things that influence the strength of your bones, how to measure bone strength, and how you can build bone.
Understanding of Bone Health
Recently I was asked to give a talk for the Ottawa chapter of the lymphoma support group. The title of my talk was as you see here, Healthy Bones, The Inside Story, The Impact of Exercise During and Following Cancer Treatments.
I thought I would share it with my listeners as a blog and so the talk we had was an hour in length and I do realize that it’s a long time and so I’ve broken it up into two sections. Just so that you know what the two sections will be covering.
In section one, understanding bone health and this is really good information for anybody, it’s all general information on bone health.
And in section two, will be more specific to cancer care where will look at exercise considerations, contraindications and precautions, getting started, and exercise guidelines.
So under section one of part one understanding of bone health, will cover the functions of bones, the types of bones that we have in our body, what type of bone cells we need to be concerned about, the definitions of bone remodelling, the influences of bone strength. How do we go about measuring bone and how do we build bone?
Functions of Bones
So functions of bones.
I have here two images and this is a cross section of a femur which is the long bone at the thigh. This top part is what is referred to as the head of the femur, the neck of the femur, and the shaft of the femur.
Here you have a magnified image where you start to see the bone on a more cellular level with veins and arteries going through the bone.
So the functions of bone. Well, we all know bone is supporting the structures in our body, protecting our internal organs. So the ribs surround our liver, the top of our stomach, our heart, and our lungs.
And bones are very critical in movement, they are important attachment points for our muscles, align leverage around joints.
Bones also play very important role in maintaining mineral homeostasis within the body as a place for blood cell production as well as a storage site for triglycerides.
Type of Bone
Types of Bone.
As you saw in the first image, there is this picture of the femur and you have this hard outer shell here, and then on the inside where it looks like more of a spongy type bone, and so those are the two types of bone, will go into them in more detail.
The outer firm bone that you see is referred to as cortical bone or hard bone. It makes up a greater portion of the peripheral skeleton, peripheral being the skeleton of the arms and legs.
It is a three layer protective outer shell around every bone in our body. 80-90% of the volume of cortical bone is calcified hence it’s a very hard bone, and it makes up 80% of our total skeletal mass.
So it provides us a significant amount of weight in its presence and so that is one of the reasons people often ask me, why do we have the softer bone? Why do we have that? Because it’s not as heavy, so the cortical bone is good but it is a heavy bone. If we were completely cortical bone, we would a lot heavier than we are.
Cortical bone has a slow turnover rate. Has a high resistance to bending and torsion. It provides strength where bending would be undesirable.
So if you think about areas of the body, you know you’re jumping, you don’t want a lot of bending in the long bones of your lower legs, your upper legs. When you’re doing pushups or taking a lot of loads with your upper body, you don’t want your humerus, they’ve or your radius and all knotted be doing a lot of bending. That shock absorption is the role of the softer bone within our body or trabecular bone.
So here you see the image of spines and each individual spinal bone. The top spinal bone is portraying a healthier bone where you have a multitude of little tiny openings amongst the scaffoldings of rods, sorry rods and cones as they’re referred to.
A little vertical and horizontal structures or scaffolding and within the context of today’s talk, when cancer starts to affect bone in the same way that lack of estrogen or other nutrient deficiencies or medications can affect bone.
You start to get an erosion of the trabecular bones. So here you see a bone that is becoming more osteoporotic and here’s a very extreme osteoporotic bone with a natural collapse of the other shell or that cortical bone getting collapsed to compressed.
So this trabecular bone is our interior scaffolding. It’s the interior scaffolding that I’ll point out of certain bones within the body, only 15 to 25% of our trabecular bone is calcified. So it’s actually very soft and like our disk as you see here between every vertebrae it acts as a shock absorber. It makes up 20% of our total skeletal mass, so it’s a good thing it’s not merely as heavy but it’s 80% of the bone surface.
So it covers a lot more ground and as a result is in contact with more substances, you know nutrient wise or health wise than our cortical bone. So it constitutes most of the bone of our axial skeleton. And that’s the bones of our skull, our ribs, the spine, and the neck of the femur which was the part between the shaft and the head that I pointed out earlier.
So here you see a skeleton demonstrating develop the proportions of cortical and trabecular bone. As you can tell into the top, the area of the thoracic spine or mid-back has one of the highest areas of your body of trabecular bone or soft bone. As you get lower down into the spine, there’s a little lower percentage of trabecular bone but still quite high in comparison to other parts of the body.
The pelvis for instance is approximately 50% cortical and 50% trabecular. The neck of the femur, sorry. I mixed my numbers up there. The pelvis is 25% trabecular, 75% cortical whereas the neck of the femur which is a high fracture site is 50% cortical and 50% trabecular. So the different parts of the body that has more trabecular bone is going to be more susceptible to fractures.
This is where the understanding of bone remodelling becomes important. Why do bones become more susceptible? Well, bones undergo something called bone remodelling and this the sum total of bone resorption and bone formation.
So you have bones that are…they have constantly being reabsorbed or replaced and new bone being formed. And this is really important because otherwise we all have you know bone growing older and no replacement happening. So the function of bone remodelling is that you’re getting a constant repairing of micro damage, you’re getting reshaping of bone to accommodate growth and mechanical usage.
So if you take up a sport and this is especially true in your early years where you know, that sport is providing you with constant impact in your legs and body’s going, wow, you know Janine is really working hard in her legs and it really need to you know be ready for all of that hard pull from her quadriceps on the femur and I want to really strengthen this up. Or your skipping rope and that constant impact, those kind of things stimulate the bone and the bone does reshape to accommodate that growth and mechanical usage.
Another function for bone remodelling is that it provides the body with a source of calcium and that calcium always allows the body to have that reservoir so that the extra cellular calcium levels are maintained at healthier level. Bone remodelling takes time and the actual process of taking over all bone and building new bone can take up to 200 days. And so far as bone turnover at the entire skeleton, that can take between 8 and 12 years. So the wait is somewhere between 8 and 12% per year.
So bone resorption. Here is an image to help you understand it a little bit better but you get these osteoclasts which are ruffled bordered cells. The clasts will help you remember the C, that there cleaners or cutters of bone. They release acid. They look like little jelly fish, that’s how I remember them, that release acid into the bonny tissue and it dissolves the minerals.
So this has its own time frame. Approximately two weeks of cleaning up the whole bone.
And then you have the formation phase where now that there’s a nice cavity that’s been formed, the osteoblasts or the builders of bone can come in and start to fill in the cavity and that can you know take a total of three to four months before that’s filled in and then you know the whole cycle is repeating itself but it’s repeating itself on a constant basis.
Determinants of Bone Health
So what are the determinants of bone health, that ensure that you know our bones are staying healthy and they’re remodelling at a healthy rate. Well, there’s quite a few determinants of that. One of them, you have no control over is your genetics. At least and so far as the way the world is today, we have no control over.
The other one is your nutritional intake, your alcohol intake. Whether you have food sensitivities, allergies, all of that will affect your ability to absorb nutrients. Your activity and exercise is very much a determinant of bone health.
As imaging before how the bone remodels based on the activity that is being signalled to the bones by the muscle pulling on the bone, by the impact of the bone on the ground. And then very importantly, hormones play a very big role in the determinant of bone health and this is especially seen in the amount of bone growth, the years surrounding puberty.
So when the two to three years surrounding puberty, girls and boys will build approximately 26% of their entire bone mass that they will have in their adult life. So the combination of the hormones and if they have an optimal level of activity and nutrition during those time, that can really set them off for a good start in life in so far as their bone health.
And lastly in terms of determinants of bone health is medication and well-being. And since this talk is focusing on cancer survivors, the medication that I will talk about is based more on cancer survivors.
Cancer Treatment-Induced Bone Loss
So there is a cancer treatment-induced bone loss and that is a very well known term for the bone loss that occurs because of the treatments that are currently used for cancer. Chemotherapy we know, causes reduced bone mass. There’s a CMF which is an abbreviation for 3 anti-cancer agent formula, that has been on these things are life saving or can be life saving but unfortunately their impact on bone is that it you know it does have a…shown reduction of bone density up to 6.5% which is not recovered once chemotherapy is stopped.
Tamoxifen we know in premenopausal women increases fracture risk by 32% after five years. In post menopausal women, Tamoxifen actually has protective effect on bone.
And cancer treatment induced bone loss is most commonly seeing in patients with breast and prostate cancer who received the chemotherapy, hormone therapy, or surgical castration. Obviously because of the double effect on hormones, which is one of the big areas at… we we spoke about earlier.
And then low bone mass is found in patients with lymphoma treated with corticosteroids, radiation or alkylating agents.
There are a long lists, there is a long lists of other medications that affect bone and then didn’t have room in this talk to give that to you but if you go to the, in our website, do you have a long lists of medications that affect bone.
Measuring Bone Density
So how do we know what our bone health is?
Unfortunately, right now the only tool that we have measures bone density and not bone quality and that’s an unfortunate thing. But if you look at bone density done through a DEXA, bone mineral density test, is in read in grams of bones per cm2. Your T-score and your Z-score are two numbers that you will often received.
Your T-score quantifies the difference between your bone mineral density at your current age and the peak bone mass for a young healthy person. So you’re being compared to somebody usually a female at their peak. So roughly about 25 years old. And the Z-score quantifies you between your bone marrow density at your current age and the peak bone mass of your peers. So is comparing you to two of your peers. Bone and density is just one part of the equation, bone quality is the second.
Bone Quality and Bone Health
Bone quality is the ability of your bones to resist the fracture because we know that some people with good bone density might have poor bone quality and therefore still fracture.
So bone quality is unaccounted for in bone mineral density measurements. It’s the sum of all the other characteristics of the bone. So what type of mineral matrix deposits happen? What kind of collagen? What have the bones been exposed to through exercise, through movement, through impact? Those are the things that will alter the quality of the bone.
So one of the consequences of poor bone strength? Well, one is obvious and that’s fractures. And not all fractures lead to pain but they do certainly lead to limited movement and reduce quality of life.
Common Fracture Sites
And where are the most common fractures sites? Well, if we go back to looking at the types of bones, the areas in our bodies that have the more trabecular bone will be more impacted. So the spine, our wrists, our hips, and for individuals, the cancer survivors or facing the diagnosis of cancer, the location of bone metastasis is also a consideration as a potential fracture site.
So a couple of slides here on spinal fractures, there are more common than hip fractures and over five years the incidence of death is as high as some do with the hip fracture. But the thing is, if somebody gets a hip fracture, they get a lot of attention and a medical system is setup to put them on the fast track to rehabilitation and being mindful of their bones but unfortunately most spinal fractures occur silently.
And therefore, sometime people have pain, 50% don’t have pain and they occur silently, might have little back ache but then you’re still at a high risk for a second and third final fracture which is why over five years the multiple spinal fractures increase your incidents of death and decrease your longevity.
So in so far as keeping your spine safe and you’ll see a lot of information on MelioGuide about protecting your spine. Learning not to bend at your spine, where you’ll be compressing bone that’s already potentially weakened but rather bending from the hip, from the knee, and keeping your spine in good alignment. Throughout all your daily activities this is so very important.
Bone is a Living Tissue
Bone as a living tissue, it requires mechanical stimulation to remain healthy. So the last thing that I want you to do is get a diagnosis of low bone density, or osteoporosis, or you have diagnosis of cancer and you’re concerned about your bones as well as so many other things to be concerned about.
But your bones need you to stay active. Bone cells are responsive to mechanical signals.
When a load or stress is applied to bone, bone is deformed. But should be deformed just enough that it stimulates the bone and not breaks the bone. So this is where working with a health care professional that is aware of your health status and is able to gradually inclement the stresses into your bodies so that you get a progressive increase in loading to keep you safe but to get you stronger is so very critical.
Key Principles of Bone Building
So what are the key bone building principles? Site specificity, high mechanical strain rate, weight bearing, novel patterns of bone loading, and loading frequency. Will cover up each of these.
1. Effect of Exercise is Site Specific
So we know that exercise sees effect is very site specific. Meaning that exercises for the upper body will not impact the bone strength of the lower body and vice versa.
2. Mechanical Loading
We also know that mechanical loading is good. Loads that contribute to bone building are things like, gravitational forces, muscle forces, ground reaction forces, you just need to find the right forces to keep your bones healthy and keeping them healthy, keep building them but keeping them safe from fracture.
3. High Mechanical Strain
So with that, although we know that high mechanical strains are very good for the bones and that high loads with sets of 8-12 repetitions in the 70-90% 1 RM range has been shown to be very good for bone. Having said that, I would never start somebody who has been de-conditioned for months or years on that mechanical strain load.
So you would want to start with lower loads, higher repetitions, gradually building into the load that we know helps to build bone health. We also know that running and jumping induce great ground reaction forces so much so, somewhere in the order of three to six times your body weight, but it doesn’t mean that everybody is ready for it. So we want to load the body in a safe and progressive manner.
4. Weight Bearing is Better Thank Non-Weight Bearing Activities
Weight-bearing we know is better than non-weight-bearing when it comes to bone health, and so weight-bearing exercises are more effective in the density of the bone but if you are in situation that the only exercises you can do comfortably are non-weight-bearing, cycling or swimming, I would not ever discourage you from doing those things, because either so many either great benefits but you would do them in view of gradually getting in more weight bearing as time progresses.
5. Novel Patterns of Bone Loading
And then when it comes to patterns of loading bones. You want to have novel patterns, meaning doing different things as much as possible. So if you love to do squat, great but challenge yourself with maybe hitting a few of the stair cases on route and going up and down stairs, or doing crossover steps or taking up a dance class so that you are introducing different patterns of loading on your bone from going uphill and downhill.
These are all great ways to load your bone and when it comes to weight training there’s hundreds, you’ve probably noticed with magazines and the media that there is always a new way to stimulate you know the biceps or your thigh muscles but you want to make sure that you’re doing it within such a way that is safe for you. But changing things up is a great thing for keeping things interesting but your bones really enjoy it as well.
6. Loading Frequency
And the loading frequency and I get this a lot, when people say, do we have to do this all at once? But they know it’s even better if you can break it up. So mechanical loading protocols are more bone building if your load cycles are divided into several discreet bouts.
So you might go for a breast walk in the morning, do your weights before lunch. If you and I’m assuming I’m saying this protocol for someone who’s retired or on holiday or you like you know slip in a breast walk at lunch and you know do your weights before going to work, those kind of things.
Just breaking it up even we know, that you know several hours of separation, just remembered that if you’re doing an exercise, protocol that requires a warm up, that you’d still allow yourself a few minutes of warm up before going into it. If you have had several hours of rest or break in between.
So talking about the break, if you are wanting to take a break, this is an opportune time but some of you, you know are really anxious to get into part two or section two I should say. So I don’t want to keep you hanging but I am going to pause here and you can go right into section two of the blog.
Thank you for tuning in MelioGuide for section one part one of the blog on cancer and bone health.
For more articles like this, visit my Osteoporosis Guidelines page.