It's no secret that being active and participating in sports can have a positive effect on bone health, but did you know that the type of sport you choose can make a big difference? Active children and adults typically boast higher bone mineral density (BMD) and enjoy a lower risk of fractures compared to their non-athletic peers. However, when we take a closer look at sports like running, biking, and swimming, we find that the bone-strengthening benefits of sport might not be the same. In fact, some endurance athletes might even have lower-than-normal BMD, increasing their risk for stress fractures and bone fragility.
In this article, we cover bone health for the endurance athlete and take a close look at the nutritional and mechanical factors that help and hurt bone health.
Understanding Bone Health: What You Need to Know
Bone Mineral Density (BMD): To assess bone health, healthcare and sports science practitioners will look at your bone mineral density (BMD). BMD is the measure of choice for bones because a higher BMD is associated with bones that are more durable and able to withstand more impact. We can compare how dense an athlete's bones are by using what is called a Z-Score. This statistical method compares a person's BMD with age- and sex-matched controls, essentially looking at how far your BMD is from a “similar” population.
Athletic Bone Profiles: Athletic populations typically have stronger bone profiles than non-athletes, so we have a higher expectation for athlete BMD. For instance, a Z-Score of -1.0 in a normal population would be suboptimal, but generally not a large concern. However, a runner with a -1.0 Z-Score would be labeled as having “low BMD” and may be at risk for bone-stress injuries.
Bone Development Over Time: Bone development is an ongoing process but is critical during our growing years, from infancy to adolescence. As we grow, protein, calcium, and other various minerals from the diet are deposited in the bone matrix. Osteoblasts and osteoclasts collaborate in bone remodeling: osteoblasts create new bone tissue, while osteoclasts break down old or damaged bone tissue, allowing new, healthier tissue to replace it.
Peak Bone Mass: The rate at which we lay down new bone peaks around adolescence, with total accrual of BMD and content peaking around the early to mid-20's. At about 30 years of age for Women and 40 years of age for Men, we start to see “age-related” declines in BMD. This is where every year, BMD gradually declines, due in large part from greater bone resorption compared to bone formation. Men having higher BMD have a delay in the time course of age-related bone loss. For females, their bone loss is further accelerated around menopause when the protective effects of estrogen on bone start to diminish.
While age-related declines in bone mass are inevitable, understanding the factors that help promote bone health can help us fight to keep our bones strong.
Mechanical Stress: The Key to Strong Bones
There are two main factors that can help us improve (or at least slow the decline of) our BMD: mechanical stress and adequate nutrition.
The Role of Mechanical Loading: Mechanical loading has arguably the greatest impact on bone health. Mechanotactic theory explains that bone responds to the magnitude, rate, total number, and direction of loading cycles induced by activity. Simply put, bone will adapt to the magnitude of load you place on it. This theory is evident when we compare bone density across sports. Athletes in higher-impact sports with larger phenotypes often have higher BMD, while those in leaner sports with less load-bearing have less BMD.
Impact of Sports on Bone Health:
Endurance athletes, who typically have smaller, slimmer frames, and often steer away from resistance training, may experience less mechanical loading on their bones. Even in sports like running, where there is a frequent impact stimulus on the bones through pounding in their legs, there may not be enough variability or load progression to positively impact their bones. Within sport differences in BMD are also observed—sprinters, for example, tend to have higher BMD and more muscle than distance runners. In sports like swimming and cycling, there is almost no mechanical load, and thus BMD rates for these sports are often (but not always) below those of runners.
But is it really just the absence of loading in these athletes that makes the difference? Cross-sectional studies in female junior and collegiate runners have shown increased rates of low BMD. In one study of 93 high school cross-country runners ages 13 to 18, 28% had Z-scores of −1 or less, and 11.8% had Z-Scores of −2 or less. For reference, a -2 Z-Score with one other risk factor is considered Osteoporosis. It was determined that runners with menstrual irregularities, dietary restraint, low lean tissue mass, and five or greater seasons of running were more likely to have low BMD in this study.
So mechanical loading alone may not be the only risk factor for poor bone health, but limited progressive mechanical loading, over time, with inadequate nutrition to cover the costs of growth, repair, and biology might be a better explanation. So what nutritional factors should be taken into consideration when we talk about bone health?
Nutritional Adequacy: Fueling Your Bones
Low Energy Availability (LEA) and Bone Health: High-volume endurance training demands energy from the body. When energy intake is not matched to output (your training), the body may not have enough resources to pay the “biological bills.” This is called low energy availability (LEA), and long-term it can lead to relative energy deficiency in sports (RED-S). LEA / RED-S can be caused by a lack of dietary intake, an overload of training, or a combination of the two. LEA can decrease levels of thyroid hormones, insulin-like growth factor 1 (IGF-1), and insulin, among others, all of which help promote bone growth.
Signs of LEA and RED-S: Feeding studies have shown that food ingestion before, during, and after exercise can increase markers of bone development and decrease markers of bone breakdown. A hallmark sign of LEA / RED-S is a reduction in markers of bone growth in the short term, and reduced BMD in the long term. Unfortunately, these signs of bone breakdown are below the surface, so many endurance athletes don't realize there's a problem until the damage is done. In runners this may manifest in stress fractures that increase in frequency and severity. For cyclists and swimmers, they may not realize anything is wrong for a long time due to the non impact nature of their sport. By the time they have a bone break or see an orthopedic specialist, the loss of bone mass could be substantial.
Nutrients That Matter for Bone Health
Below is a summary of key nutrients that play crucial roles in maintaining bone health:
Protein: Supports bone collagen structure and hormone production, aiding muscle mass and bone health. Sources: Meats, dairy, eggs, fish, nuts, and beans.
Calcium: Essential for bone formation; 99% of body calcium is in bones. Low calcium intake can harm bone health. Sources: Dairy, leafy greens, and beans.
Phosphorus: Important for bone mineralization. Balance with calcium is crucial. Sources: Dairy, meats, fish, and nuts.
Vitamin D: Facilitates calcium and phosphorus absorption.
Sources: Fatty fish, fortified foods, and sunlight exposure.
Magnesium: Vital for bone structure and function, affecting both osteoblasts and osteoclasts. Sources: Whole grains, nuts, and leafy greens.
Zinc: Aids in bone tissue mineralization and may support vitamin D's action. Sources: Meats, shellfish, and legumes.
Vitamin K: Important for bone protein formation and reducing fracture risk. Sources: Green leafy vegetables like kale, spinach, and broccoli.
Vitamin C: Crucial for collagen synthesis, important for bone strength. Sources: Fruits like kiwi, guava, strawberries, and citrus as well as certain vegetables like broccoli and brussels sprouts.
Other Factors to Consider
NSAID Use: Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used by athletes for pain and inflammation management. However, chronic use of NSAIDs has been linked to impaired bone healing and may negatively affect bone density. It's recommended to take NSAIDs after exercise if necessary, as this timing may help avoid interference with the bone remodeling process that occurs during recovery.
Caffeine and Alcohol: Caffeine, widely used by athletes for its performance-enhancing effects, can lead to increased calcium excretion in urine, potentially impacting bone health. However, moderate caffeine consumption does not seem to significantly affect bone health if calcium intake is adequate. Similarly, alcohol should be consumed in moderation, as excessive intake is known to negatively impact bone density (among other things).
Actionable Items for Endurance Athletes
Calcium Needs:
Aim for 1,000-1,300 mg/day of calcium.
Don’t avoid dairy if you’re not allergic or sensitive to lactose.
Spread calcium intake throughout the day (300-500 mg at a time) for best absorption.
Don't avoid dairy if you’re not allergic or sensitive to lactose. Opt for lactose-free options like Fairlife milk, or fortified non-dairy milks if sensitive to lactose.
Augment dairy intake with other calcium fortified or rich foods like fruit juices and drinks, tofu, ready-to-eat cereal, broccoli, kale, and cabbage.
Adequate Vitamin D:
Aim for 600-800 IU/day.
Understand that sunscreen, pollution, northern latitudes, and darker skin types may increase sun exposure time needed for adequate Vitamin D.
NSAIDs:
If NSAIDs are necessary, consider taking them after exercise rather than before.
Caffeine and Alcohol:
Keep habitual caffeine consumption under 400 mg per day.
Limit alcohol intake to less than one drink per day on average.
Maintain Energy Balance:
Ensure that your caloric intake matches your energy expenditure to preserve bone health.
Getting a bone (DXA) scan, and interpreting the results.
How to coordinate your nutrition with a plan from your PT or strength coach.
Understanding metabolic blood tests and when/where to get tested.
Is supplementation is needed? If so what type of product is safe and effective.
Supplement timing.
Understanding health risks with deficiency or excessive dosages of vitamins / minerals.
How to adjust environmental factors for Vitamin D exposure.
Nutritional methods of pain / inflammation reduction.
Nutritional ways to support healing of bone stress injuries.
Understanding how to maintain energy balance for your training.
Conclusion
Ultimately, there are a host of factors to consider when it comes to bone health. Dietitians are sharpening their skills and finding new and better ways to help athletes not only improve their performance but also preserve long-term bone health. By focusing on the right balance of mechanical loading, nutrition, and overall health, you can keep your bones strong and healthy for years to come. Get in contact with us today to learn more about what this means for you!
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