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Bone Loss: A Primer

It's crucial to understand the workings of the skeleton and the risks of bone loss.

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Graphic of human body and skeleton to show bone loss

How much do you really know about bones? Although bones are vital to life itself, knowledge and interventions geared at preventing unnecessary bone loss and subsequent osteopenia and osteoporosis are still lacking. According to the Surgeon General, “The biggest problem is a lack of awareness of bone disease among both the public and health care professionals” (OSG 2004).

Bone loss and sarcopenia (muscle loss) are a normal part of aging, and being aware of the pathophysiology of these processes can help fitness professionals to develop effective preventive strategies and to better inform clients. Consider that half of women over 50 and a quarter of their male counterparts suffer broken bones because of osteoporosis (NOF 2016). Health authorities project about 17.2 million new cases of osteoporosis or osteopenia between 2010 and 2030, a 32% growth rate compared with 2005–2010 (Wright et al. 2014). No doubt, you’re aware of the ample opportunity—and great earnings potential—in this population.

To excel at informing these clients and helping them develop effective preventive strategies, you need insight on the basic pathophysiology of aging bone. We’ll start by reviewing how bones grow, why they shrink with age, and what the difference is between osteoporosis and osteopenia.

Bone Modeling and Remodeling

The skeleton is composed of two types of bone: cortical and trabecular. Cortical (compact) bone comprises 80% of the volume in the adult skeleton and forms the outer layer of bone (Lerner 2012). Trabecular (cancellous) bone makes up the inner layer; has a spongy, honeycomb structure; and is mostly found in the skull, pelvis, sacrum and vertebrae. Although peak bone mass is reached in late adolescence, bones never stop changing. An adult skeleton replaces its bone mass every 10 years (OSG 2004).

Bones adapt via processes called “modeling” and “remodeling”:

Modeling—formation of new bone in one site and removal of old bone in another—occurs during childhood and adolescence. This process allows bone to grow in size and shift in space so the skeleton can adapt on the way to adulthood. Modeling is crucial to bone because it’s in the modeling years that peak bone mass develops—a significant indicator of fracture risk in later life (Rizzoli 2014). A 10% higher peak bone mass may delay the development of osteoporosis by 13 years (Hernandez, Beaupre & Carter 2003).

Remodeling happens in the fully-formed adult skeleton. Remodeling does not change the size or shape of bones; it gradually replaces them.

Osteoblasts, Osteoclasts and Osteocytes

Three types of cells make modeling and remodeling possible: osteoblasts, osteoclasts and osteocytes. Osteoblasts form bone and cause it to mineralize. Osteoclasts do the opposite, degrading bone tissue. An optimum balance between osteoclasts and osteoblasts keeps bone mass constant. Too many osteoclasts cause too much bone to be dissolved, shrinking bone mass, but if osteoclasts are too few, bones will not be hollowed out enough for the marrow. Both of these imbalances can cause osteoporosis (Gilbert 2000).

Osteocytes, the third kind of cell, originate from osteoblasts and make up 90% of all bone cells (Lerner 2012). Osteocytes are deeply embedded in cortical and trabecular bone tissue and have extensive dendritic (branching) processes through which they communicate with osteoblasts and other osteocytes. These signaling pathways play a crucial role in the skeleton’s ability to continually adapt in response to mechanical loading, because osteocytes can sense total mechanical load and trigger biomechanical responses. These responses can either encourage formation of new bone to handle heavier loads or remove bone in the absence of load (Bonewald 2006).

The Bone-Muscle Unit

Mechanical loading is the most important determinant of bone strength, influencing muscle size and force, which in turn correlate with bone mineral density (BMD) (Tagliaferri et al. 2015). We call this concept the “bone-muscle unit” because the development of one directly influences the other. This unit has extra importance during childhood and adolescence because accruing lean tissue mass during the formative years affects adult bone strength (Tagliaferri et al. 2015). If you work with children and adolescents, the bone-muscle unit represents a prime opportunity to influence present and future bone health.

See also: Strategies for Preventing Bone Loss

Bone Loss and Aging

Bone loss and aging are inseparable: “The skeleton is a systemically regulated mass of mineralized material that is born, grows, reaches a more or less high peak, and then declines faster or slower as to develop a correspondingly high or low fracture risk”(Ferretti et al. 2003). Musculoskeletal aging—declining bone and muscle mass, increasing joint pain and stiffness, and decreasing physical mobility—is a normal part of aging. However, how rapidly or slowly bone mass declines depends on different factors. While genetic abnormalities account for 70% of the variance in skeletal strength (Rizzoli 2014), other factors—like hormones, nutrition, physical activity and toxins—play crucial roles in developing bone and losing it.

Understanding bone loss starts with distinguishing between the two basic diagnoses: osteopenia (low bone mass) and osteoporosis (advanced loss of bone tissue). Then, the smart thing to do is learn about risk factors and preventive measures.

Osteopenia vs. Osteoporosis

More clients may come to you with a diagnosis of osteopenia than with the better-known osteoporosis. Osteopenia points to low bone mass when overall bone mineral density hasn’t fallen far enough to cause serious concern. It’s critical to note that an osteopenia diagnosis does not mean osteoporosis is inevitable. How­ever, if a client mentions this diagnosis, you have an excellent opportunity to explain that physical activity and nutrition are important modifiable factors that can prevent further decline.

We distinguish between osteopenia and osteoporosis via the T-score system, which quantifies BMD (Karaguzel & Holick 2010). Because the T-score measures bone loss, it is expressed as a negative number. A T-score between -1
and -2.5 is defined as osteopenia, while a T-score below -2.5 is defined as osteoporosis.

There are two types of osteoporosis, both characterized by weakened bone and increased risk for fracture: primary (bone loss through aging) and secondary (caused by a variety of diseases, medications and toxic agents). We will focus only on primary osteoporosis since it is the more common type and also the type that fitness professionals can help clients with through physical activity and nutrition.

Osteoporosis is often called the “silent disease” because it’s usually not diagnosed until after a fracture (Porter et al. 2016). Indeed, nearly 80% of older adults who suffer bone breaks have never been tested or treated for osteoporosis (NOF 2016). Following a fracture, the risks of mortality and disability accelerate: 1 in 5 hip fracture patients end up in a nursing home (OSG 2004), and 24% of hip fracture patients over 50 die in the year after the fracture (NOF 2016).

Thus, fitness professionals who help older exercisers confront the risk factors of osteoporosis can be lifesavers.

See also: Bone Density and Healthy Aging

Diet, Exercise and Bone Loss

As a fitness pro, you can’t fix the genetic and environmental contributors to bone loss, but you can encourage physical activity and proper nutrition, both of which improve bone health. More than 70% of Americans don’t get the recommended amount of physical activity (Laskowski 2012), and 50% are considered deficient in vitamin D (Karaguzel & Holick 2010). One systematic review rated calcium, vitamin D, dairy and physical activity/exercise as the most important modifiable lifestyle factors that can influence the development of peak bone mass (NOF 2016).

Nutrition

Proper diet pulls double duty: developing skeletal strength and maintaining bone’s role as a mineral storehouse. Minerals such as calcium and phosphorus, which the body must have in order to perform every day, are stored in bone. If the body can’t get these minerals from our diet, it takes them from our bones, reducing bone mass and strength (OSG 2004).

After age 30, calcium deficiencies can lead to a gradual bone loss as high as 0.5% per year (Karaguzel & Holick 2010). Calcium is a crucial part of young people’s diets, as half of the calcium in the adult skeleton is deposited during the ages of 13–17 (Karaguzel & Holick 2010).

Consuming calcium on its own, however, is not enough. Proper absorption of calcium depends on sufficient vitamin D intake, and some research has even suggested that calcium supplements without vitamin D supplementation may increase the risk of myocardial infarction (Rizzoli 2014). Interestingly, this increased risk is not evident when calcium is consumed from food, which is the intake method that is most highly recommended. Calcium can be obtained from a variety of food sources and, even for people with dietary restrictions such as dairy intolerance, there are many food sources available.

Dairy products, however, are the most efficient way to get enough calcium. One study evaluated the importance of dairy in calcium delivery and found that although calcium supplements can influence bone remodeling, dairy products have an additional benefit for bone growth. Dairy products provide more calcium, protein, magnesium, potassium, zinc and phosphorus per calorie than any other food (Rizzoli 2014). It would take 48 servings of whole grains or 24 servings of green vegetables to provide as much calcium as there is in a 200-millileter (6.76-ounce) glass of milk.

You may also have seen milk advertised as the perfect postworkout drink. Research into the effectiveness of fat-free milk versus an isoenergetic carbohydrate drink after resistance training found that milk promoted fat loss, lean-mass gains and BMD (Rizzoli 2014). Because calcium and vitamin D go hand in hand, many milks and yogurts are now fortified with vitamin D. Note that exposure to sunlight is still the most effective way to get enough vitamin D (Karaguzel & Holick 2010).

Although vitamin D is the main factor in calcium absorption, research suggests that absorption increases with higher dietary protein consumption in postmenopausal women (Tagliaferri et al. 2015) and that higher protein intake correlates to a lower rate of age-related bone loss (IOF 2017).

Note: Be aware of your scope of practice. You can inform clients about nutrition, but you cannot prescribe specific nutrients. Always refer your clients to their physician. In fact, suggesting they talk to their physician about bone health could be a motivating factor. Studies show that patients who are aware of their BMD numbers and fracture risk are more likely to adjust their calcium intake (Rizzoli 2014).

See also: Bone Up on Vegan Nutrition

Physical Activity

According to the Surgeon General, physical activity “is one of the most important controllable lifestyle changes to help prevent (or reduce the risk of) a number of chronic diseases” (OSG 2004), and although it is a leading health indicator, more than 80% of adults do not meet the guidelines for both aerobic and muscle-strengthening activities (ODPHP 2018).

McMillan et al. (2017) state that physical inactivity, or sedentary behavior, has been described as “the major public health problem of our time.” Physical activity is known to influence both bone and muscle metabolism; therefore, inactivity—or a decline in activity—can affect bone through those two pathways (Tagliaferri et al. 2015). Osteogenesis occurs in response to mechanical loading. Inactivity, with its lack of loading, prevents bones from receiving the signal to adapt, which causes bone loss. It’s a basic use-it-or-lose-it scenario.

While all exercises affect muscle and bone, recent research indicates that some activities help bones more than others. In program development, it is important to consider that the skeletal sites closest to the engaged muscle will have the biggest BMD increases (McMillan et al. 2017). For example, in sprinters and shot putters, BMD is highest in the legs and dominant arm, respectively. This is helpful to know when working with clients who have compromised BMD in certain sites.

Muscles are the key factor in exerting mechanical force on the skeleton, so increasing muscle strength is important—especially in the bones most likely to fracture (hips, wrists, vertebrae, etc.). See the sidebar “Activities and Bone Health” for bone-building exercises.

Making Bone Health a Priority

You probably don’t have many clients coming in and saying, “I want to grow a strong skeleton.” But you know that skeletal health is an essential foundation for all the work fitness professionals do. Therefore, prioritize knowing the basics of bone development and loss and figuring out how to help your clients grow and retain the strongest bones possible.



Bone Basics

  • Calcium, vitamin D, dairy and physical activity are critical to preserving and building bone mass.
  • Bone mass peaks in the early 20s.
  • BMD = bone mineral density (measured in T-score, a negative number because it quantifies bone loss).
  • Osteopenia is the onset of bone loss (T-score -1 to -2.5).
  • Osteoporosis is the most serious bone loss (T-score below -2.5).
  • Walking has limited effect on bone health.
  • Progressive resistance training helps to maintain and improve BMD.
  • High-impact activities help the most with bone growth.
  • Posture and balance training are essential to fall prevention.
  • Heavy resistance training is safe and improves bone, function and stature.
  • Women over 50 have the highest risk of osteoporosis and fractures.

Activities and Bone Health

Walking

Walking is often the top recommendation for osteoporosis, even though a plethora of studies have shown it has only a limited effect on bone (McMillan et al. 2017; Karaguzel & Holick 2010; Watson et al. 2015). If combined with impact and resistance training, however, walking can help maintain BMD in the hip region and in the lumbar and sacral spine (Karaguzel & Holick 2010). In people over 65, increasing daily steps by 25% has been associated with an increase in hip BMD (McMillan et al. 2017).

Progressive Resistance Training (PRT)

PRT is the most widely researched method for preserving BMD. It has proved to be the most effective way to increase BMD in women and older adults and to maintain BMD in men (McMillan et al. 2017). Resistance training also improves muscle mass and strength (Karaguzel & Holick 2010), both of which are crucial to osteogenesis (bone formation) as well as fall prevention, which becomes a more pronounced risk in older adults.

Emphasize exercises that target posture muscles, such as back and spinal extensors, and that increase strength in functional movements, such as stair climbing or box squats. Greater back extensor strength has been associated with lower risk of vertebral fracture and thoracic kyphosis, which correlate with balance impairment (IOF 2017; Giangregorio et al. 2014).

High-Impact Exercise

Activities that produce a weighted impact on the skeleton are especially osteogenic. The most osteogenic activities induce high-magnitude strains in bone at a high rate (Watson et al. 2015). Brief, high-impact exercises such as hopping, skipping and jumping can increase BMD, muscle strength and power (McMillan et al. 2017). Adding unilateral and multiplanar components—such as single-leg hopping or side, front and back hops—can improve balance and proprioception, two key factors in fall prevention.

High-Intensity Progressive Resistance Training (HiPRT)

HiPRT combines heavy resistance training with high-impact activities. This type of training has proved to be effective for postmenopausal women with low to very low bone mass (Watson et al. 2015). The combination of progressively increasing weight in resistance exercises while boosting impact loading in high-intensity exercises can enhance bone mass, physical function and posture while decreasing the risk of osteoporotic fracture (Watson et al. 2015). Postural improvement is noticeable with a reduction in thoracic kyphosis.

Posture and Balance Training

Staying upright and standing without falling are crucial everyday skills we often take for granted because they happen automatically (Lacour, Bernard-Demanze & Dumitrescu 2008). The posture-control system depends on multiple inputs—visual, vestibular, proprioceptive somatosensory and tactile somatosensory—and these can become compromised as we age (Chiba et al. 2016; Lacour, Bernard-Demanze & Dumitrescu 2008). As dynamic and static postural tasks become much more challenging, it gets more difficult to perform a cognitive task at the same time, and the body prioritizes posture control over cognitive-task performance to avoid falling. This is known as the “posture first” principle (Lacour, Bernard-Demanze & Dumitrescu 2008). Being aware of posture-first principles can help you design programs for older adults or other clients with posture and balance impairments.

Emphasize exercises that incorporate two tasks, such as walking and talking, or that challenge the exerciser to close the eyes (visual), use a tilting platform (proprioceptive) or use a foam mat (tactile).

Bone Health in Women

Fitness professionals have to be aware of just how great the osteoporotic fracture risk is for women. Worldwide, osteoporosis affects 200 million women, and the lifetime risk of a hip fracture is 1 in 6, compared with 1 in 9 for breast cancer (IOF 2017).

The risk for postmenopausal women is even higher. Most fractures occur in postmenopausal women, and the lifetime fracture risk for a 50-year-old woman with osteoporosis is as high as 60% (IOF 2017; Karaguzel & Holick 2010). To frame it another way: A woman’s risk of hip fracture is equal to her combined risks of breast, uterine and ovarian cancer (NOF 2016).

When working with clients who have had a previous fracture, it is important to know that 1 in 5 women with a vertebral fracture will experience a second one within 1 year (Karaguzel & Holick 2010). Thus, program development should prioritize avoiding the second fracture.

Most fitness pros have female clients, and some even specialize in working with postmenopausal clients. Thus, staying aware of the increased fracture risk puts you in a good position, not only to educate clients about the risk, but also to provide them with workouts that prioritize bone health as well as muscle mass.

Exercises for Clients With Osteoporosis

When working with any clients diagnosed with osteoporosis, you want to maximize the benefit, but you must also take care to avoid unnecessary risk. If mobility and posture are altered after a vertebral fracture, pay close attention to correct lifting technique and avoid pitfalls such as loading the spine in a flexed posture. For example, since exercise machines often require twisting and forward bending, you may need to avoid using them with clients who have osteoporosis (Giangregorio et al. 2014). Also, tailor the intensity and type of exercise to minimize chronic pain—a condition that is common in clients with a previous osteoporotic fracture.

Resistance Training

Include all major muscle groups at least twice a week.

  • Include 2 sets per exercise, 8–12 reps per set.
  • Avoid exercise machines.
  • Use slow and controlled movements.

Balance

Aim for 15–20 minutes daily to accumulate at least 2 hours a week.

  • Include three-dimensional exercises such as tai chi.
  • Encourage lifestyle-integrated exercises:
    • tandem stance while washing dishes
    • closing eyes while doing static tasks

Aerobic Training

Do not use this to the exclusion of resistance or balance training. Aim for 150–300 minutes per week of moderate-intensity exercise or 75–150 minutes of vigorous exercise.

  • Include exercises with dynamic, high-force movements (jumping, skipping).
  • With clients at high risk of vertebral fracture, do not do vigorous exercise or dynamic, high-force exercises.

Source: Giangregorio et al. 2014.

References

Bonewald, L.F. 2006. Mechanosensation and transduction in osteocytes. Bonekey Osteovision, 3 (10), 7–15.

Chiba, R., et al. 2016. Human upright posture control models based on multisensory inputs; in fast and slow dynamics. Neuroscience Research, 104, 96–104.

Ferretti, J.L., et al. 2003. Bone mass, bone strength, muscle-bone interactions, osteopenias and osteoporoses. Mechanisms of Ageing and Development, 124 (3), 269–79.

Giangregorio, L.M., et al. 2014. Too fit to fracture: Exercise recommendations for individuals with osteoporosis or osteoporotic vertebral fracture. Osteoporosis International, 25 (3), 821–35.

Gilbert, S.F. 2000. Developmental Biology (6th ed.). Sunderland, MA: Sinauer Associates.

Hernandez C.J., Beaupre, G.S., & Carter, D.R. 2003. A theoretical analysis of the relative influences of peak BMD, age-related bone loss and menopause on the development of osteoporosis. Osteoporosis International, 14, 843–7.

IOF (International Osteoporosis Foundation). 2017. Facts and statistics. Accessed Mar. 3, 2018: iofbonehealth.org/facts-statistics.

Karaguzel, G., & Holick, M.F. 2010. Diagnosis and treatment of osteopenia. Reviews in Endocrine and Metabolic Disorders, 11 (4), 237–51.

Lacour, M., Bernard-Demanze, L., & Dumitrescu, M. 2008. Posture control, aging, and attention resources: Models and posture-analysis methods. Neurophysiologie Clinique, 38 (6), 411–21.

Laskowski, E.R. 2012. The role of exercise in the treatment of obesity. PM & R: The Journal of Injury, Function, and Rehabilitation, 4 (11), 840–44.

Lerner, U.H. 2012. Osteoblasts, osteoclasts, and osteocytes: Unveiling their intimate-associated responses to applied orthodontic forces. Seminars in Orthodontics, 18 (4), 237–48.

McMillan, L.B., et al. 2017. Prescribing physical activity for the prevention and treatment of osteoporosis in older adults. Healthcare, 5 (4), e85.

NIH (National Institutes of Health). n.d. Trabecular bone. Accessed Mar. 19, 2018: ncbi.nlm.nih.gov/pubmedhealth/PMHT0022808/.

NOF (National Osteoporosis Foundation). 2016. Accessed Mar. 19, 2018: nof.org.

ODPHP (Office of Disease Prevention and Health Promotion). 2018. Physical activity. Accessed Mar. 19, 2018: healthypeople.gov.

OSG (Office of the Surgeon General). 2004. Bone health and osteoporosis: A report of the Surgeon General. Accessed Mar. 3, 2018: ncbi.nlm.nih.gov/books/NBK45513/.

Porter, J., et al. 2016. The effect of dietary interventions and nutritional supplementation on bone mineral density in otherwise healthy adults with osteopenia: A systematic review. Nutrition Bulletin, 41 (2), 108–21.

Rizzoli, R. 2014. Nutritional aspects of bone health. Clinical Endocrinology & Metabolism, 28 (6), 795–808.

Tagliaferri, C., et al. 2015. Muscle and bone, two interconnected tissues. Ageing Research Reviews, 21, 55–70.

Watson, S.L., et al. 2015. Heavy resistance training is safe and improves bone, function, and stature in postmenopausal women with low to very low bone mass: Novel early findings from the LIFTMOR trial. Osteoporosis International, 26 (12), 2889–94.

Wright, N.C., et al. 2014. The recent prevalence of osteoporosis and low bone mass in the United States based on bone mineral density at the femoral neck or lumbar spine. Journal of Bone Mineral Research, 29 (11), 2520–26.

Maria Luque, PhD, MS, CHES

Maria Luque, PhD, is a health educator, fitness expert, presenter, writer and USAF veteran. She created Fitness in Menopause, a company dedicated to helping women navigate the challenges and rewards of menopause. Her course “Menopausal Fitness: Training the Menopausal Client” is NASM-, AFAA- and ACE- accredited. She holds graduate and postgraduate degrees in health sciences and teaches at the College of Health and Human Services at Trident University International.

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