This topic is of particular interest to those at risk for osteoporosis. I would contest, however, that it is applicable to all because the prescription for bone health will also assist in maintaining muscle mass, something we will all gradually lose without great intention and effort.
What is Bone?
There are three basic parts to the anatomy of a bone. The outside layer is hard, and quite dense. This is called the cortex or cortical layer. The density of this layer is what we measure with a Bone Mineral Density (BMD) test (a.k.a. DEXA scan). This comprises the entire surface of the bone, but the majority is located in the shaft of a long bone, like the femur.
The trabecular bone or “spongy bone” looks like a lattice-work and is located primarily at each end of the bone. This is the part of the bone that gives it its real strength. Of course cortical bone is hard, but we all know something hard can also be brittle. This lattice-work gives bone its tensile strength. If we put a long bone in a vice, and pulled on each end until it snapped, this would be its tensile strength. We don’t have a test to replicate this, so for now, we use a DEXA. Our bones have a great amount of tensile strength when we’re born because bones at that point, are much more like rubber. As we age and the bone mineralizes, it becomes harder and more dense, eventually reaching full maturity around 20 years of age.
The last part of the anatomy is the bone marrow, responsible for making the majority of your Red Blood Cells (RBCs) and White Blood Cells (WBCs). It also houses your memory B & T-cells that are responsible for recognizing a prior pathogen (virus or bacteria) and wiping it out before it can reinfect someone.
The Cellular Level: Osteoblasts vs. Osteoclasts
Osteoblasts are responsible for building bone through the deposition of collagen bone matrix and then mineralizing it. This increases bone density.
Osteoclasts are responsible for resorbing bone through the liberation of calcium. We are constantly remodeling our bones based on the stresses we expose them to. Osteoclasts decrease bone density in and of themselves, but combined with the osteoblasts and with the right stresses, they are necessary for building stronger bones through the remodeling process. Think of it like the demolition process involved in putting an addition on a house or remodeling a room.
Through the combined effort of these two cells, we turn over our skeleton roughly every 10 years.
Vitamin D, Calcium, and Parathyroid Hormone (PTH)
Vitamin D helps our gut to absorb calcium. For those of us old enough to remember, rickets is a disease in childhood where bones fail to mineralize because of lack of calcium, ultimately because of a severe vitamin D deficiency. Our bones are the largest reservoir of Calcium in our body, and so if we are deficient in calcium somewhere in the body, we can draw it out of bone. When calcium levels are low, PTH goes up, and that stimulates bone to release calcium. It will also stimulate the kidney to change vitamin D from it’s inactive form (D2) to its active form (D3) and thus increase calcium absorption in the gut.
The Consequences of Poor Bone Health
Accidental deaths are much less common now than they used to be. But as we age, we need to be more concerned. Under the age of 60, an overdose is the most common cause of accidental death. But after 65, falls are the primary cause of accidental death, and after 75, falls are the fourth leading cause of all deaths behind only Alzheimer’s, cancer, and heart disease.
When we fall at 25 we bounce off the ground. When we fall at 80 we break a bone. The older we are, the more likely we are to die from the same forces acting upon us. The graph above does not show total deaths, but rather deaths per 100k people. This helps us to take into account the decline in population as we age and thus demonstrates how fragile we become because even though there are very few people aged 85 years and older, compared with those in the 25-34 year old age group, the number of accidental deaths per 100k in the older group is far greater.
Studies on excess mortality after hip fracture differ, but the trend is easily noticeable. One study from 2010 showed the following:
A larger study of 122,808 participants, at least 60 years old, in the US & Europe, were followed for 12.6 years. Out of 4273 fractures and 27,999 deaths in this period, the hazard ratio (HR) for hip fracture was 2.12 for the full 12.6 years, and 2.78 within the first year of fracture. Translated, this means people in the study who experienced a hip fracture were 278% more likely to die within a year compared to people of similar demographics who did not fracture a hip. Putting this in some context, current smokers 60 years and older have a HR of 2.07.
How do we Measure Bone Strength?
The ideal test, would be to put a bone in a vise, and apply tangential forces to it, until it breaks, thus giving us the shear strength of the bone. It would be a test that would evaluate both the cortical and trabecular components. Since this is unrealistic, we have to settle on using a machine called a DEXA (dual-energy xray absorptiometry) scanner. With this we can get a sense for how strong bone is. This machine measures the 2D density of cortical bone (not trabecular bone like is shown in figure 3). It gives us two measurements: T-score & Z-score, taken at the hip and lumbar spine (the areas most likely to fracture due to weak bone).
T-score compares you to a young, healthy adult
Z-score compares you to someone your own age and gender
Osteopenia represents bone loss of at least 10% and is defined as a T-score between -1.0 and -2.5. Each point equals one standard deviation away from the mean. So a T-score of -1.0 means you have a lower bone density than 82.5% of the population, and a higher bone density than 17.5% of the population. Of course a T-score of 0 means your are right in the middle, 50%/50%.
Osteoporosis represents 25% bone loss and is defined as a T-score of -2.5 and below. For reference, a T-score of -2.0 translates to weaker bone than 97.5% and stronger bone than only 2.5%.
Severe Osteoporosis is defined as a T-score of -2.5 and below with a history of an osteoporotic fracture
When should I get my First DEXA Scan?
The recommendations from most organizations (including those below) consist of women starting screening at 65 and men at 70, and high risk patients at 50 years of age.
The World Health Organization (WHO) recommends starting screening at age 40. I tend to agree with the WHO. I think individuals with risk factors need to be screened much earlier than in their 7th decade, especially because we see fractures occurring in patients much younger than this with undiagnosed osteoporosis. There are certain patients we know have zero risk factors and don’t need a DEXA at 40, but for $100, we could certainly be guiding patients at a much earlier stage toward better bone health and thus preventing osteoporosis in the first place.
How to Achieve Peak Bone Potential and Maintain it: Factors Affecting Bone Health
Our bones reach full genetic potential by the time we are 20 years old. This means we should be encouraging the younger generations to adopt healthy habits and discourage the harmful things that keep them from reaching their full genetic potential. Risk factors include the following:
We want to encourage adequate nourishment, especially adequate protein intake, and activity in things that load the skeleton. Running and cycling in and of themselves are not going to get our kids to their peak potential. However, sports and activities involving jumping, lifting heavy things, or even contact sports (i.e. hockey, lacrosse, football), are going to increase bone mineralization much more. High power output over a short time span (i.e. explosive movements) are key to building strong bone.
Another example is that golf using a cart will not load your bones, but walking a golf course with your loaded golf bag, will provide some signal to the osteoblasts to strengthen your bones.
The “Female Athlete Triad” is defined as low BMI, poor bone health, and hormone dysregulation. This is common amongst high schoolers in sports such as cross country where low body weight is advantageous to performing well in the sport.
20-50 years old
Maintaining the practices above are very important: nutritional intake, resistance training, avoiding factors that inhibit bone deposition or increase resorption. As you can see in figure 3, this is truly the maintenance period. One nuance is that if someone does not reach peak potential by age 20, one can still achieve peak potential by age 50, if they work extra hard at it. The system is flexible enough to support this type of drastic improvement in bone deposition and mineralization.
Menopause and the last decades
There is a reason why estrogen is more effective than any other drug at improving BMD scores. Muscles attach to bones via tendons. When muscle contracts, the tendon acts at its insertion or origin site on bone, and sends a signal to the osteoblasts in the vicinity of the tendon that a force is being applied. Without estrogen, the signal is significantly diminished. This is why we are not shy about hormone replacement therapy in our practice. A 2014 Mayo Clinic study showed that in postmenopausal women, osteoporotic fracture (4.9m) leads to more hospitalizations than heart attack (2.9m), stroke (3m), or breast cancer (700k). Some studies such as this one show the ability of estrogen replacement to lower the risk of fracture by up to 50%. That beats any prescription drug around, even when used in combination.
This is also where we need to double click on weight-bearing exercises. Each day we observe the tendency of the 60+ year old individual minimizing their daily activity. Whether for reasons of injury, low energy, or just following the crowd, I find that patients, especially after 60 years old, tend to move and exercise less. This tendency is something that must be actively resisted. Weight bearing exercises and resistance training are especially neglected in these years and therefore represent a great opportunity for us to gain back lost ground. This video shows a clinic utilizing powerlifting to combat women and men already diagnosed with osteoporosis to reverse the process and improve bone mineralization. In our practice, we encourage resistance training starting at an early age and continued throughout the lifespan. We also have introductory plans for patients in their later decades who have never been exposed to powerlifting exercises.
A note on nutrition: Protein intake and its impact on muscle mass
Because muscle size and function is so integrated with the dynamics of bone health, it is important to maintain our muscle mass. We also need substrate for our osteoblasts to lay down the organic matrix to maintain bone structure. The best source for this is protein. At our practice we recommend a daily protein intake of 2g/kg bodyweight. We don’t care how people get it in, we just want that goal to be achieved. Liquid protein is not off the table.
This is all in the name of avoiding sarcopenia. Sarcopenia is effectively the loss of muscle mass as measured on a DEXA scan. ASM (appendicular skeletal muscle mass) is the muscle we have on our arms and legs. We can find this out from a DEXA scan. If we take this number and account for height, a number of 7 kg/m2 for men and 5.5kg/m2 for women, define “sarcopenia.”
This is avoided via the inputs (protein mass and quality) and the signals (weight bearing exercise) we provide our bodies. If our muscles are replaced with fat and connective tissue via sarcopenia, then we decrease the stress on our bones during muscle contraction. This will decrease the signal to the osteoblasts to deposit more bone. It simply follows that someone with low muscle mass will also have a low BMD.
Main Takeaways to Improve and Maintain Bone Health