Jan 29, 2015
Inner Strength

When it comes to bone health, there are many pieces to the puzzle. It’s likely your athletes are missing some of them in their everyday lives.

By Michelle Rockwell

Michelle Rockwell, MS, RD, CSSD, is a Sports Dietitian based in Raleigh-Durham, N.C. She works with athletes at North Carolina State University and serves as a consultant to teams and individual athletes nationwide. She is also co-founder of RK Team Nutrition and can be reached at: www.rkteamnutrition.com.

A college running back fractures his ankle during preseason workouts and is healing at a very slow pace, surprising the team’s athletic trainers and frustrating his coaches. He spends most of the season on the sidelines.

A top high school runner is diagnosed with her third shin stress fracture in two years, causing her to miss a second consecutive state championship cross country meet. She aggressively supplements with calcium and feels she has a healthy diet, so is confused by the repeat injury.

A star collegiate point guard fractures her foot during a late-season game. A non-contact injury, she doesn’t recall any twisting or odd landing–it “just happened.” She ends up missing the league’s tournament championships, greatly impacting her team’s performance.

When we think of unexplained fractures and slow healing of bones, we usually relate these problems with the elderly. However, every year, bone injuries take a serious toll on high school and college athletes, as well as their sports medicine support staffs, coaches, teammates, and families. In many cases, these injuries can be chalked up to sub-optimal bone health.


Bone is a dynamic, growing tissue made up of the protein collagen and several minerals–mainly calcium phosphate. Throughout our life span, bone is continually “remodeled” through resorption and formation. When new bone tissue replaces old, the cells involved in bone formation are called osteoblasts. There are numerous hormones such as estrogen, testosterone, calcitonin, parathyroid hormone, and vitamin D (which has hormone-like properties) involved in this process. As healthy children and teenagers develop, bone formation exceeds resorption and their bones become larger, stronger, and more dense. Between the ages of 20 and 30, however, bones do not continue to build density. In fact, bone mass declines throughout the remainder of life. Clearly, it is critical for young people to maximize bone development through diet, exercise, and lifestyle.

Bone mineral density (BMD) is a measure of the amount of bone tissue in a certain volume of bone–in other words, bone strength. BMD includes assessment of the calcium content of bones. Research shows that in many cases, BMD is a reliable predictor of fracture risk.

Dual-energy x-ray absorptiometry (DXA, previously referred to as DEXA) is a type of x-ray based on bone densitometry. DXA is currently considered the gold standard for measuring bone density. Different areas of bone are measured based on the test and protocol, but common sites include the spine, hip, femur, and wrist. (It is important to not confuse DXA scans with bone scans, in which a radioactive tracer is injected to detect medical problems in bones.)

For individuals over 21 years of age, results of DXA scans are expressed in T-scores, which are standard deviations from the mean of expected bone density based on age and gender. T-scores above -1.0 (less than 1 standard deviation below the mean) are considered normal. T-scores between -1.0 and -2.5 are classified as osteopenia, which means low bone mass. T-scores below -2.5 are classified as osteoporosis, which literally means “porous” bones.

The appearance of osteoporotic bone marrow is brittle, with large holes. Normal bone, on the other hand, has small holes and is stronger and more resistant to fracture.

Interpreting DXA scan results for individuals under 21 years of age is more complicated since less normative data has been established for this age group. Instead of T-scores, results are expressed in Z-scores. Like T-scores, Z-scores are based on data from individuals of the same age and gender, but they also take into account race, height, and weight. However, more data needs to be collected on the younger population to establish reliable mean scores.

When interpreting Z-scores, those with scores less than -2.0 are considered to have “low bone mineral content” or “low bone mineral density for age.” The term osteoporosis is not used in people under 21 years of age unless they also meet other criteria, such as having previously suffered fractures.

In many cases, the greatest benefit of DXA scans in young athletes is to examine and monitor trends. Changes in bone density require six months to one year to accumulate, but they can be very revealing.

For example, I have seen a female athlete with a baseline Z-score of -0.7 (normal) develop a Z-score of -2.2 exactly one year later, following disordered eating patterns, a loss of over 15 percent of her body weight, and strict adherence to a vegan diet with very few calcium sources and no supplementation. On the other hand, a female runner increased her Z-score from the “low bone density” category to normal within 18 months, after increasing her intake of calcium and fat, restoring menstrual function, and supplementing with vitamin D. She also improved her running times.


What exactly predisposes athletes to low BMD, which research has shown to be a reliable predictor of stress fracture risk? Although genetics play a role, there are numerous other controllable factors that come into play.

Medical History: Having had one stress fracture is believed to be a strong predictor of future stress fractures. Once an athlete incurs a stress fracture, additional attention should be paid to uncovering likely causes and contributors in order to prevent future injuries.

Bone Development: Failing to maximize bone development during younger years will likely increase risk of bone problems in athletes during high school and college. The good news is that bone mass accumulation continues through at least the early 20s, so intervention during high school and college years can make a significant acute and life-long impact.

Inadequate Calories: When athletes do not consume enough calories to meet needs, it is known as negative energy availability. If this becomes an ongoing pattern, it can lead to low BMD.

Low body weight in relation to height is commonly correlated with low BMD. Increasing body weight to a more appropriate range–typically through additional calorie intake or perhaps strength training–can improve BMD.

Male athletes should not be disregarded in this category. Energy deficit, undereating, and low levels of testosterone can contribute to decreased levels of BMD in men.

Menstrual Abnormalities: Current or previous menstrual abnormalities such as amenorrhea (absence of menstruation) or oligomenorrhea (sometimes defined as fewer than four periods in one year) are considered strong predictors of low BMD and fracture risk. Menstrual dysfunction often occurs secondary to low estrogen levels. Low estrogen plays a role in weakening bones, partially through its association with weakened concentrations of blood formation markers. It has been estimated that for every year of low estrogen levels, a five to 10 percent decrease in bone mineral density may occur.

There are multiple causes for menstrual abnormalities, some primarily medical in nature. However, chronic consumption of inadequate calories has been shown to have a strong relationship to menstrual problems. Thus, treating menstrual abnormalities with birth control pills or other hormones may or may not be helpful to increasing bone mass, since a low calorie intake appears to be the root of the problem.

The Triad: The Female Athlete Triad–the known relationship among disordered eating, decreased BMD, and menstrual abnormalities–is a clear cause of bone injury and poor bone healing. While some individuals with the Female Athlete Triad have distinct clinically diagnosable eating disorders such as anorexia nervosa or bulimia nervosa, there are numerous others whose eating behaviors would be classified as disordered eating. These individuals are also at risk for bone problems.

Intense Running Training: In general, weight-bearing exercise enhances BMD. However, at the high mileage level required in some sports, BMD can actually be compromised. Highly competitive runners and soccer players, for example, have been shown to have reduced BMD (regardless of diet and menstrual history) compared to control subjects in a few research studies. In terms of running, it seems that there is a threshold, at which point BMD can be hindered instead of helped, but it varies widely by individual based on previous training, diet history, and body weight. Research in this area is just starting to take hold.

Typically, women are often thought to be at greater risk for stress fractures. However, in distance running and track and field, several studies have reported a similar incidence among high school and college-aged males and females.

Calcium Intake: According to the Food and Nutrition Board’s Dietary Reference Intakes, high school and college-aged individuals should consume 1,000 to 1,300 milligrams of calcium per day. However, research has shown that, on average, high school and college students fail to consume this recommended amount. High school students in particular are not even meeting half of their daily needs. Broad-spread calcium intake has been shown to be so inadequate that the most recent Dietary Guidelines for Americans (2005) lists improving milk, dairy, or other calcium intake as a specific target.

Furthermore, it has also been shown that athletes may have enhanced calcium needs for various reasons. Thus, calcium intake should clearly be addressed, preferably via diet, or supplements if necessary.

Although not known to be extremely common, some athletes lose a significant amount of calcium through sweat. Calcium is one of many electrolytes lost in sweat, so someone who has a high concentration of calcium in their sweat or who simply sweats at a high volume regularly may need to increase their calcium intake.

Consider the compilation of calcium issues that may occur in one athlete. Suppose he or she consumes calcium below recommended levels, doesn’t tolerate dairy well before practice or competition, and has a high sweat calcium rate. This individual may have higher risk of calcium deficiency–compromising bone health–than obvious at first glance.

Vitamin D: An extensive amount of information about vitamin D and its role in health and disease prevention has been uncovered in recent years. However, it has been understood for quite a long time that vitamin D is essential for calcium absorption. Thus, increasing calcium may be fairly futile if vitamin D levels are sub-par.

A recent report showed that 60 percent of Americans take in too little vitamin D, based on the current Recommended Daily Allowance of 400 IU per day. Many experts feel this level is actually too low and athletes are frequently advised to supplement with 1,000 IU per day.

Other Vitamins and Minerals: There are additional vitamins and minerals that are known to be associated with bone health and mass, namely vitamin K, potassium, and magnesium. There are not specific recommendations for these micronutrients as they relate to bone, but a diet rich in fruits, vegetables, dairy, and whole grains can help athletes obtain ideal levels of these nutrients.

Other Macronutrients: Even if an individual is consuming adequate calories, studies have shown that dietary fat and protein are both contributors to healthy bones. Many athletes develop the mindset that extremely high carbohydrate diets are important to enhance performance, but healthy fats and lean proteins are also critical. However, it is possible that extremely high protein diets may decrease BMD.

Other Medical Problems: Abnormalities in thyroid hormones and other medical problems may contribute to decreased BMD. Certain medications may also impact BMD. Athletes should consult with their physician about any bone effects their health conditions or prescribed medications may predispose them to.

Tobacco and Alcohol Use: Researchers have shown a relationship between regular tobacco use and consumption of less than eight to 10 alcoholic beverages per week and a weakening of bones. Education on this negative byproduct of tobacco and alcohol use can be beneficial to athletes.


Because there are so many factors related to keeping bones strong, advice to athletes in this area must be multi-pronged. It should include education, screenings, and teamwork.

When educating high school and college athletes, it’s critical they understand they are in a bone-building life phase–taking care of their bones now can help them prevent osteoporosis and other bone-related issues later in life. Up to 45 percent of women and 30 percent of men over 65 years of age experience osteoporosis or non-trauma-related fractures.

But since convincing young people to worry about their future health is not always effective, take the time to explain how all the factors mentioned above can help them stay strong now and not miss any playing time with a stress fracture. I suggest focusing on the following areas:

• The bone consequences of consuming too few calories or of chronic dieting: Some athletes, both male and female, chronically under-consume calories either intentionally (perhaps as a method of weight control) or unintentionally due to time demands, lack of appetite, or poor education about calorie needs to support their daily expenditure. They need to know the negative effects of such practices.

• How to include adequate protein and healthy fats in their diets: A big greasy bacon-cheeseburger has a lot of protein and fat, but also a lot of calories. Educate athletes on how to consume lean protein, such as chicken and fish, and fats from heart-healthy oils, nuts, avocados, and olives.

• Adequate consumption of calcium-rich foods or supplements: It is recommended that athletes get 1,500 milligrams a day of calcium. Provide suggestions on how athletes can add calcium to their diet through milk, low-fat cheese, and yogurt.

Some athletes consume minimal or no dairy products because they are lactose intolerant, vegan, or have some discomfort after consuming dairy. Medications are available to help those with true lactose intolerance, and lactose-free dairy products or calcium-fortified soy milks, yogurts, and cheeses are excellent alternatives. Salmon, almonds, fortified cereals, and some green vegetables are also good calcium sources.

• How to get enough vitamin D: Researchers have learned vitamin D synthesis from sunlight is not quite as efficient as once believed and that sunscreen blocks up to 95 percent of vitamin D synthesis. This is particularly relevant for athletes who participate in indoor sports or train minimally outside. People living at a similar latitude to Atlanta, Ga., are likely to need two hours of sunlight to obtain adequate vitamin D synthesis. Those with darker skin typically have lower levels of vitamin D.

• Consequences of tobacco and alcohol use on bones: Today’s student-athletes often receive preventative education about using tobacco and alcohol. Letting them know about its negative effects on bone health can give them one more reason to say no to these products.

Screenings can also be helpful in spotting and preventing bone problems. To start, consider DXA screening for athletes, at least those with particular risk factors for low BMD. DXA testing costs anywhere from $200 to $400, but is covered by many insurance companies in certain scenarios (such as history of stress fractures or an eating disorder).

Levels of vitamin D can be checked through blood tests, which has proven beneficial for many collegiate programs and individual athletes. A blood level of 32 ng/ml of 25-hydroxy-vitamin D is recommended and some experts feel that as high as 50 ng/ml is appropriate.

A common supplement regimen for low vitamin D levels is either 1,000 to 1,500 IU a day for eight weeks or 10,000 IU once a week for eight weeks prior to retesting. If you do not have access to vitamin D testing, there is little risk in taking 1,000 IU per day.

Finally, teamwork is also important. Athletic trainers, strength and conditioning coaches, sport coaches, and team physicians all play roles in helping athletes achieve bone health.

Coaches should understand the possible effects of high mileage training and should be encouraged to limit mileage or alter the workout type or intensity when an individual has low BMD. Athletic trainers should talk with athletes about their menstrual cycles and those with abnormal menstruation should be screened by a physician. In addition, sports nutritionists can be included on the team to provide education and counseling for individual athletes.

High school and college athletes often take bone health for granted. Unless a fracture rears its ugly head, they trust that the structure helping them to run, jump, and throw is solid. But a clearer understanding of how bones stay strong and some preventative methods can go a long way toward ensuring our athletes stay healthy today and tomorrow.

Sidebar: FOLLOW UP

The three athletes mentioned at the beginning of this article are all real people who needed real solutions. An individualized treatment plan was developed for each, with good results.

The running back with the slow-healing ankle fracture perplexed the medical team because he was very compliant to treatment and rehab. He also said he drank a gallon of milk every two days, in addition to consuming several other dairy sources, so calcium intake was not likely the problem.

However, a vitamin D blood test revealed a level of only 11 ng/ml, while the normal level is 32 ng/ml. The athlete was not able to absorb all of the calcium he was taking in due to a vitamin D deficiency. It turns out he was training and rehabbing almost exclusively indoors, and distinct improvements in healing came after six weeks of high-dose supplementation.

The high school runner spent a lot of time exploring her repeated stress fractures with her sports dietitian and pediatrician. She was a very conscientious eater, consuming about 1,000 milligrams of calcium a day along with an additional 600-milligram supplement. She regularly read books and magazines about nutrition and had most every food label memorized. She was aiming for 2,000 calories per day, which she believed to be appropriate since she was smaller than the average “adult” at only 109 pounds. She reported that she did not start menstruating until age 16 and since that point, had only had three very erratic periods.

This athlete was diagnosed with the Female Athlete Triad. She did not have a clinically diagnosable eating disorder, but she did have menstrual abnormality, decreased bone mineral density (her Z-score was -2.8), and was chronically in negative energy balance. She was burning about 3,200 calories a day, and over time, that 1,200 calorie per day deficit accumulated and became problematic. Although it took some work to convince the athlete that her energy needs were significantly higher than 2,000 calories, she complied. Her menstrual cycle became normal after six months on a higher calorie diet and she is now in her second year running for an NCAA Division I program where she has not experienced any more bone injuries.

Our point guard with the surprise foot fracture had never really worried much about her nutrition. At 14 percent body fat and great strength, she could eat anything she wanted–and she did! Her diet contained a lot of fast foods, soda, and convenience store foods. Analysis by her sports dietitian revealed that she was not only consuming less than a quarter of her calcium needs, but that she had been doing so since she was a young child. She had several lactose intolerant family members and never consumed milk or dairy products except an occasional slice of pizza. A good calcium supplementation regimen was key for this athlete’s healing.


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