Take control of your bone health
Exercise and sport, which put stress and strain on your bone, are generally positive for overall bone health. However, there are some conditions surrounding sport that can be harmful to your bone. Your nutritional status and body weight, whether your sport is weight-bearing or not, and the amount of rest you build into your training program are all factors that can contribute to bone health. Bone stress injuries, commonly referred to as “stress fractures” or stress reactions, can thwart your training goals or prematurely end your season.
Below we will cover important determinants of bone health for female athletes and tips for improving or maintaining your bone mineral density throughout your life.
Your bone health from youth to adulthood
Through optimal nutrition and weight-bearing physical activity as young athletes, we maximise our ability to build bone. Adolescence is considered prime time for bone-building.1 Throughout life, our bones undergo constant bone remodelling. During this process, mature bone tissue is removed, which is called bone resorption or breakdown, while new tissue is formed, referred to as bone formation.
These processes work together and occur in response to different types of, or in the absence of, bone stress or strain. When we are young, we tip the scale towards more bone formation. A healthy person will reach their peak bone mass in their mid to late 20s. As a young adult, bone remodelling typically is in maintenance mode. Later in life, the scale tips towards more bone resorption.
Especially for post-menopausal (meaning that more than a year has passed since your last menstrual period) women, it becomes difficult to maintain the same bone mineral density as they previously had. There are many factors that can contribute to a diagnosis of osteoporosis in females. The hormonal changes that occur in the peri- and post-menopausal period are contributors.
The WHO defines osteoporosis as ‘a progressive systemic skeletal disease characterised by low bone mineral density (BMD) and micro-architectural deterioration of bone tissue, with consequent increase in bone fragility and susceptibility of fracture.’ A loss of BMD leaves your bones more fragile to breaks (fractures) and less able to withstand acute trauma or chronic stress.
Bone stress injuries
Although you may participate in sport without experiencing any symptoms related to low BMD, findings of low BMD put you at a higher risk for fractures, including traumatic fractures and bone stress injuries.
A traumatic fracture can be defined as an acute physical injury of sudden onset, for example, a broken collar bone or broken wrist resulting from a bike crash.
A bone stress injury results when your bone is unable to withstand repetitive, mechanical loading (impact) due to factors that disrupt your bone load, bone strength, or bone remodelling. These injuries exist along a continuum that starts with microscopic damage, commonly referred to as stress reaction, and can progress to stress fractures at the most extreme end of the spectrum. Compared with other athletes, they occur most often in competitive cross-country and track-and-field athletes. Furthermore, female athletes suffer bone stress injuries more frequently than their male counterparts2.
One reason you should care about bone stress injuries is that they may be a sign of a broader, systemic deficit in your metabolic, hormonal, or nutritional status. For example, insufficient caloric intake and/or excessive energy expenditure may result in low energy availability (LEA) and can impact your bone health.
How bone health is assessed
Lower BMD is independently associated with increased bone stress injury risk. BMD measurement is widely applied to assess bone health by using dual-energy X-ray absorptiometry (DXA). A DXA scan separates your body into soft tissue and bone. It measures BMD to determine if your bones are thinner or more porous compared to healthy young adults of similar age and sex.
Experts use the Z-score, which compares your bone density to the average bone density of people your own age and gender. A low Z-score is a warning sign that you have less bone mass and/or lose bone more rapidly than expected for a woman your age.
The American College of Sports Medicine defines low BMD in young premenopausal weight-bearing female athletes as a Z-score from < -1 to -2, and osteoporosis as a Z-score of -2.0 SD in the setting of clinical risk factors for fracture. According to the International Society for Clinical Densitometry (ISCD) for premenopausal women, a Z-score of -2.0 SD is considered “below expected range for age.” Osteoporosis is defined as a BMD Z-score -2.0 SD plus risk factors for fracture or secondary causes of osteoporosis. For children and adolescents, diagnosis of osteoporosis is only applied when the BMD Z-score is -2.0 SD and there is a clinically significant fracture history.
If you are diagnosed with bone stress injuries, the extent and focus of the additional workup may depend on your DXA results, along with an assessment of your risk factors based on a history and physical exam. This workup should be conducted by a sports medicine physician with experience in bone health and management of bone stress injuries. Treatment for impaired bone health varies based on severity, and a complete discussion is beyond the scope of this article. Instead, our focus will be on the measures you can take today to optimise your bone health.
RED-S, the Female Athlete Triad, and nutrition
As previously mentioned, low energy availability (LEA) can have a negative impact on overall bone health. In 1992, the Female Athlete Triad was introduced to describe the relationship between LEA, menstrual function, and BMD. Later, in 2007, each component of the Triad was described as existing along a continuum between optimal health and significant disease (Figure below). At one end of the spectrum, an athlete has adequate energy availability, regular periods, and optimal bone health. Further along the spectrum, an athlete may have reduced energy availability, irregular periods and/or low BMD. At the pathologic end of the spectrum, an athlete may have LEA with or without disordered eating/eating disorder, complete absence of periods, and osteoporosis.3
LEA is the underlying cause of the Triad. The more comprehensive term relative energy deficiency in sport or RED-S (was introduced by the International Olympic Committee (IOC)4 more recently. It describes a mismatch between energy intake through the diet and the demands of exercise and the body’s energy needs for basic physiological function (hormones, muscle, cardiovascular health, enzymes, and metabolism). Symptoms of RED- are multifaceted and described in a recent article on RED-S on this platform.
Low energy availability
In athletes, LEA can occur intentionally through dietary restriction or excessive energy expenditure. LEA may be unintentional when your sport expends large amounts of energy which you don’t realise. You may then consume inadequate calories to meet your energy needs. Energy intake for optimal body function has been measured in the laboratory to be approximately 45 kcal/kg/fat-free mass per day, whereas LEA has been noted as 30 kcal/kg/fat-free mass per day for women, although this varies individually.
When you are in a chronic state of LEA, it puts your bone at risk. When your body lacks energy, it also lacks nutrients from food, including minerals, such as calcium and vitamin D. Since the body prioritises its most essential functions, your bone health may suffer. An example of this would be the bone releasing calcium into the bloodstream when blood calcium is low to enable other functions. such as regulating your heart rhythm and muscular function.
Ideally, there is enough calcium in your food to support all physiological needs. Working with a qualified Sports Dietitian or Sports Nutritionist can help you to clearly understand your energy needs, including the quality, timing, and quantity of energy intake that’s optimal for your athletic endeavours.
Rest and recovery
Lack of rest and recovery in athletes is another important factor that can contribute to bone stress injuries. Bone requires rest and proper nutrition to adapt to stress and strain. Overtraining, in combination with poor nutrition, impairs healthy bone remodelling as bone is constantly being broken down. Making sure your training plan balances optimal rest with work and energy intake will play an integral role in protecting yourself from unnecessary bone stress injuries.
Vitamins and minerals
Vitamins and minerals play an important role in bone health, including but not limited to, calcium, phosphorous, vitamin D, and collagen. Ideally, you should aim to meet most of these aspects of your nutrition through food. It’s been shown that calcium from food is more effective than supplements for optimising bone health. This could be due to the food matrix and how the nutrients in a food work in symbiosis.
When you are in a chronic state of LEA, getting sufficient vitamins and minerals from food becomes increasingly challenging. Many athletes have cupboards full of supplements in an effort to bridge nutrition gaps not being met through their diet. We would strongly recommend that you optimise your food intake first and then re-assess if there are legitimate deficiencies through blood tests.
Calcium is the most abundant mineral in your bone, and over 99% of the body’s calcium is stored in bones and teeth. Calcium can be from both animal and non-animal food sources. Some of the best calcium-rich foods include dairy (milk, yogurt, cheese, cottage cheese), salmon with bones, dark leafy greens, beans, soybeans, tofu, nuts and seeds, and fortified nut milks and juices.
Using fortified milk in smoothies and adding tofu and dark leafy greens to stir fries can help boost your daily calcium intake. Some apps like Cronometer will track your calcium to help you see how much you are getting per day and per meal.
Dietary Reference Intakes for calcium from Health Canada (similar to National Institute of Health guidelines) are below and more details can be found here, including the tolerable upper intake level:
- Children 9–18 years: 1300 mg
- Adults 19–50 years: 1000 mg
Vitamin D is a crucial nutrient for building and maintaining healthy bone. It helps your body to absorb bone-fortifying calcium. Dietary sources of vitamin D are limited but include some fatty fish like salmon and sardines, egg yolks, milk, and fortified dairy and grain products.
Your body can synthesise vitamin D after exposure to the ultraviolet light from the sun. Therefore, some exposure to the sun without sunscreen is an important source of vitamin D. The amount of vitamin D your body can synthesise from the sun is dependant on the time of year, your skin pigmentation, sunscreen use, and your geographical location. In the Northern Hemisphere, supplementation is recommended.
Research has shown that athletes who reach their optimal vitamin D levels have a lower incidence of upper respiratory tract infections than those with vitamin D deficiencies.5 Speak with your physician if you are concerned with your vitamin D levels.
The Dietary Reference Intakes for vitamin D intake from Health Canada are listed below. A more detailed chart can be found here, including the tolerable upper-intake level:
Children and adults 9–70 years old: 600 IU (15 mcg)
Weight bearing vs. non-weight bearing sports
Young athletes who participate in multidirectional weight bearing sports, such as soccer and martial arts, have been shown to have higher bone mineral density than those who participate in non-weight bearing sports such as swimming and cycling. Although these non-weight bearing sports still have benefits for cardiovascular health and the musculature, alone they may not generate enough strain to maintain healthy bone since the body is being supported by either water or a bike.
If your sport is non-weight bearing, such as swimming and cycling, you should make a point of incorporating land training with a focus on novel multidirectional movements to stimulate your bone. Exercises that load your lumbar spine and hips, such as jumping, weighted lunges, squats, deadlifts, and push-and-pull exercises are recommended to complement these sports.
In older adults, in particular post-menopausal women, a focus on heavy lifting and novel movements becomes especially important to counteract and limit losses in BMD. Learning proper techniques from qualified trainers is important to avoid injury when progressing towards and eventually executing heavy lifts. If you are at higher fracture risk due to low bone mineral density or osteoporosis, it is important to work with a trainer who is specifically educated in this area.
Figure by Dr. Emily Kraus and Anne Guzman
Take control of your bone health
Educating yourself about bone health as an athlete can steer you away from injuries that may otherwise take you away from your sport for lengthy recovery time. Since we rarely feel symptoms of low bone mineral density, it’s important to understand the red flags and seek professional help if you have concerns. A health care professional may find it necessary to start certain medications to optimise your overall bone health, in addition to addressing the previously mentioned issues.
We’re only blessed with one set of bones, and as we’ve learned here, taking care of them early in life will set us up for a lower risk of osteoporosis later in life. Being a healthy, strong athlete with optimal nutrition and including bone loading exercises in your regular routine will set you up for longevity in both sport and life.
Take the steps now to prevent injuries and maximise your time doing what you love!
- Santos L, Elliott-Sale KJ, Sale C. Exercise and bone health across the lifespan. Biogerontology. 2017;18(6):931-946. doi:10.1007/s10522-017-9732-6
- Wentz L, Liu PY, Haymes E, Ilich JZ. Females have a greater incidence of stress fractures than males in both military and athletic populations: A systemic review. Mil Med. 2011;176(4):420-430. doi:10.7205/MILMED-D-10-00322
- Nattiv A, Loucks AB, Manore MM, Sanborn CF, Sundgot-Borgen J, Warren MP. The female athlete triad. Med Sci Sports Exerc. 2007;39(10):1867-1882. doi:10.1249/mss.0b013e318149f111
- Mountjoy M, Sundgot-Borgen JK, Burke LM, et al. IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. Br J Sports Med. 2018;52(11):687-697. doi:10.1136/bjsports-2018-099193
- He CS, Handzlik M, Fraser WD, et al. Influence of vitamin D status on respiratory infection incidence and immune function during 4 months of winter training in endurance sport Athletes. Exerc Immunol Rev. 2013;19(0):86-101.