When an athlete gets a stress fracture, what’s one of the first pieces of nutrition advice they hear? You guessed it… “Make sure you’re getting enough calcium and vitamin D.” And yes, calcium and vitamin D are important for bone health. But focusing on those two nutrients alone can make us miss a much bigger piece of the puzzle.
I like to think of calcium and vitamin D as two ingredients in a 10-ingredient recipe.
You need them, yes. But you can’t leave out the other eight ingredients and expect the recipe to turn out the same.
When it comes to an athlete’s bone health, we have to look beyond individual vitamins and minerals and ask a much bigger question:
Does this athlete have enough energy available to support bone formation, repair, and adaptation in the first place?
Because no amount of calcium or vitamin D can fully compensate for a body that is chronically underfueled.
Bone Health Is About More Than Calcium
We often think of bones as the structural framework holding our bodies together.
But bone isn’t just sitting there.
Bone is metabolically active tissue that is constantly changing.
Throughout the day, old or damaged bone is broken down through a process called bone resorption, while new bone tissue is formed through osteogenesis.
Think of it like an ongoing home renovation project.
Old material comes out. New material goes in. Damage gets repaired. The structure adapts to the demands being placed on it.
For an athlete, that adaptation is incredibly important.
Running, jumping, lifting, and other types of training repeatedly load the skeleton. When an athlete is adequately fueled and recovering well, that mechanical loading can stimulate positive adaptations in bone.
But building and repairing bone requires resources, and that’s where nutrition becomes about much more than just calcium.
What Does Calcium Do for Bone Health?
There’s a reason calcium gets so much attention when we talk about bone health.
Approximately 99% of the body’s calcium is stored in the skeleton.
But calcium isn’t only needed for bones.
It also plays an essential role in functions such as neuromuscular activity and cardiac contraction.
That means the body works hard to maintain appropriate levels of calcium in the bloodstream.
If serum calcium drops, bone can be broken down to release calcium into circulation.
In other words, your body will prioritize keeping critical systems functioning, even if maintaining those systems comes at the expense of bone.
This is one reason adequate calcium intake matters, but it also illustrates why calcium alone isn’t enough.
The goal isn’t simply to put more calcium into the body. We need to create a physiological environment in which the athlete can actually maintain and build bone.
What About Vitamin D and Bone Health?
Vitamin D is another important piece of the bone health puzzle.
That’s why evaluating vitamin D status is often part of the conversation when an athlete experiences poor bone health or recurrent bone stress injuries.
Addressing an actual vitamin D deficiency is important, but here’s where I want providers to be careful:
Correcting a vitamin D deficiency doesn’t automatically correct low energy availability.
The same is true of calcium.
An athlete can take the recommended supplement every day and still be chronically underfueled.
They can meet their calcium needs and still not consume enough total energy.
They can correct their vitamin D level while continuing to restrict carbohydrates.
They can take every supplement recommended to them and still not give their body the resources it needs to keep up with their training.
This is why supplement recommendations shouldn’t be where our assessment ends.
What Happens to Bone When an Athlete Is Underfueled?
Athletes need energy for much more than their workouts.
Their bodies are also using energy to support:
- Bone remodeling
- Hormone production
- Cardiovascular function
- Immune function
- Digestion
- Tissue repair
- Recovery
- Brain function
- Growth and development
When energy intake isn’t sufficient to support exercise and the body’s other physiological needs, the athlete may experience low energy availability (LEA), and then the body has to adapt.
It doesn’t have an unlimited amount of energy available, so it begins prioritizing the processes most critical to survival.
Your body needs to keep your heart beating.
Building stronger bones? That can become a lower priority.
Over time, inadequate energy availability can disrupt normal bone remodeling so that bone breakdown begins to outpace bone formation.
Now put that athlete through practice, and another practice, and a long run, and strength training, and competition.
The mechanical stress continues to accumulate while the body’s ability to repair and adapt to that stress is compromised.
That’s when we can start running into problems.
You Can’t Supplement Your Way Out of Chronic Underfueling
This is the point I really want providers, athletes, coaches, and parents to understand.
Calcium and vitamin D are important. But they cannot override chronic low energy availability.
If an athlete is underfueled, the answer isn’t simply adding a calcium supplement on top of an inadequate diet.
We need to address the underfueling.
This is especially important when we’re working with an athlete who has already experienced a bone stress injury.
If we focus only on calcium and vitamin D without investigating WHY the athlete’s bone health has become compromised, we may correct one or two nutrient deficiencies without addressing the bigger physiological problem.
And then we’re surprised when another injury occurs.
What Nutrients Support Bone Health in Athletes?
Strong bones aren’t built from one nutrient.
Bone formation relies on multiple nutrients and adequate overall energy intake.
Some of the nutritional pieces we need to consider include:
Total Energy
Before getting lost in micronutrients, ask whether the athlete is eating enough overall.
An athlete can have a diet that looks “healthy” on paper and still not consume enough energy to meet their physiological demands.
This is especially important as training volume changes.
If training goes up but fueling doesn’t increase with it, energy availability can decline.
Carbohydrates
Carbohydrates aren’t just about having enough energy to finish a workout.
Carbohydrate availability may also influence bone metabolism.
Research discussed in my upcoming academic book has examined the effects of both low energy availability and low carbohydrate availability on bone, suggesting that energy and carbohydrate sufficiency matter for bone formation.
That’s an important consideration in sport environments where low-carb eating or “fat adaptation” may be encouraged.
Protein
Protein provides building blocks for tissue growth and repair and is another important component of overall bone health.
Again, though, adequate protein doesn’t cancel out inadequate energy.
An athlete can hit a protein target and still be underfueled.
Calcium
Yes, calcium absolutely belongs on the list.
But instead of asking only, “Are they taking calcium?”, we need to evaluate calcium intake as one part of the athlete’s overall nutritional picture.
Vitamin D
Vitamin D status matters for skeletal health, and deficiency should be appropriately evaluated and addressed.
But vitamin D should also be viewed as one piece of a much larger assessment.
Magnesium, Phosphorus, Potassium, and Other Nutrients
Bone formation involves multiple nutrients, including magnesium, phosphorus, potassium, and others.
This is another reason adequate dietary variety matters.
The more restrictive an athlete’s diet becomes, the more opportunities there are for nutrient gaps to develop.
Is It a Micronutrient Problem or an Energy Problem?
This distinction is incredibly important when we’re assessing an athlete’s bone health.
Let’s say an athlete has inadequate calcium intake.
Why?
Maybe they’ve eliminated dairy and haven’t replaced those nutrients elsewhere.
Maybe they follow a dietary pattern that requires more intentional planning.
Maybe food allergies or intolerances are limiting their choices.
But there’s another possibility:
They’re simply not eating enough food overall.
When total intake drops, micronutrient intake often drops along with it.
That means a nutrient deficiency may not be an isolated problem.
It may be another clue pointing toward chronic low energy availability.
As providers, we need to distinguish between a nutrient gap caused by the composition of the athlete’s diet and one occurring because the athlete isn’t consuming enough total energy to meet their needs.
The treatment approach may look very different.
Dietary Restriction Can Complicate Things
Athletes are exposed to a LOT of nutrition messaging.
- Eat clean.
- Cut sugar.
- Avoid processed foods.
- Go low-carb.
- Lose body fat.
- Try plant-based.
- Eliminate dairy.
- Eat “anti-inflammatory.”
Some athletes choose dietary patterns for ethical, cultural, medical, or personal reasons, and those dietary patterns can absolutely be compatible with sport.
The concern isn’t necessarily the label attached to the diet.
The concern is whether the athlete is able to meet their total energy and nutrient needs within that dietary pattern.
As more foods or food groups disappear, meeting those needs can become more difficult.
We also have to pay attention to the WHY behind the restriction.
Is this genuinely a dietary preference?
Is the athlete managing a diagnosed medical condition?
Or has “healthy eating” gradually become a socially acceptable way to eat less?
That distinction matters when we’re evaluating both bone health and REDs risk.
Young Athletes Have Even More at Stake
This conversation becomes particularly important during adolescence.
Puberty is a critical period for increasing bone diameter and density and developing peak bone mass.
Young athletes aren’t simply fueling today’s practice.
They’re fueling growth.
They’re building the skeletal foundation they’ll carry into adulthood.
That’s why intentional caloric restriction, weight-loss efforts, or chronic underfueling during adolescence can be particularly concerning.
Most of the physiological consequences associated with REDs can improve when adequate energy availability is restored.
But prolonged disruption to bone development during this critical window may have consequences that aren’t completely reversed later.
We don’t get unlimited opportunities to build peak bone mass.
That’s why protecting bone health in young athletes needs to be about much more than handing them a calcium supplement.
Ask a Better Question About Athlete Bone Health
So instead of stopping at:
“Are you taking calcium and vitamin D?”
I want providers to ask:
“Is this athlete adequately fueled for their total physiological needs?”
Then dig deeper.
- Has training volume recently increased?
- Did food intake increase with it?
- Are they restricting carbohydrates?
- Have they eliminated food groups?
- Are they intentionally trying to lose weight or change body composition?
- Have they experienced menstrual changes or changes in libido?
- How is recovery?
- Are they experiencing recurrent bone stress injuries?
- What does their overall dietary intake look like?
- Are there other signs of REDs?
Calcium matters.
Vitamin D matters.
Protein matters.
Carbohydrates matter.
Micronutrients matter.
But none of those nutrients exist in isolation.
We have to zoom out and look at the athlete’s entire physiological and nutritional environment.
Because if an athlete doesn’t have enough energy available to support the work of building and repairing bone, adding another supplement may not solve the problem.
Calcium and vitamin D may be two important ingredients in the recipe.
But we still need the whole recipe.
Want to Become More Confident Assessing Bone Health Through a REDs-Informed Lens?
Bone health is a perfect example of why treating REDs requires us to connect the dots.
An athlete may come to you with a stress fracture, low vitamin D, menstrual changes, restrictive eating, poor recovery, or declining performance.
Individually, each issue may lead us down a different path.
But sometimes they’re pieces of the same bigger picture.
Inside my REDs Informed Provider Certification Program®, I teach providers how to screen, assess, and support athletes with REDs using a practical framework that looks beyond individual symptoms to understand what’s happening across the entire athlete.
Because becoming REDs informed isn’t about memorizing another list of symptoms.
It’s learning how to recognize the connections between them.