5 Nutrient Deficiencies That Are Silently Sabotaging Your Teen Athlete

It’s Wednesday practice, and your kid looks like they’re running through wet cement.

They’re not injured. They slept. They ate. But somewhere between Monday’s sharp opener and today, the wheels came off. Their legs are heavy. Their focus is shot. And the coach is giving you that look, the one that says your kid doesn’t look right.

You’ve probably chalked it up to a bad week, a growth spurt, or “just being a teenager.” And sometimes that’s exactly what it is. But when the pattern keeps repeating (good start, mid-week crash, sluggish weekends) it’s worth asking a different question: What if the problem isn’t effort? What if it’s fuel?

Nutrient deficiencies in teen athletes are far more common than most parents realize, and they rarely announce themselves with obvious symptoms. Instead, they show up disguised as things we explain away: fatigue, moodiness, lingering soreness, a general “flatness” that’s hard to pin down.

Here are five of the most common gaps we see, and the subtle signals your teen’s body may already be sending you.

1. Magnesium: The Invisible Recovery Bottleneck

Magnesium is involved in over 300 enzymatic reactions in the body, including muscle contraction, energy production, nervous system regulation, and sleep quality. It’s one of the hardest-working minerals in an athlete’s system, and one of the most commonly depleted through sweat and training stress.

What parents typically notice:

•   Muscle cramps or tightness that gets worse as the week goes on, especially late in games when it matters most

•   Restless, poor-quality sleep, even when they’re in bed for nine hours

•   That “heavy legs” feeling that lingers way longer than it should after hard sessions

•   A shorter fuse than usual: snappy, wired, unable to wind down at night

Where to find it: Pumpkin seeds, almonds, black beans, spinach, dark chocolate, and whole grains are all solid sources. But here’s the catch: soil depletion and modern food processing mean even a “good diet” may fall short for a teenager who’s training five days a week. In these cases, supplementation may be necessary.

2. Vitamin B12: When “Lazy” Is Actually Low

This one is sneaky. B12 drives red blood cell formation and supports the nervous system, which means it directly affects stamina, focus, and mood. When it’s low, the symptoms look a lot like a teenager who just doesn’t care. Except they do care. They’re just running on empty.

The signs that get dismissed:

•   Endurance that’s noticeably lower than teammates, or lower than their own baseline from a few months ago

•   Brain fog in school and on the field (trouble processing plays, zoning out, slow reactions)

•   Mood swings that seem to come out of nowhere

•   Persistent tiredness that sleep doesn’t fix

Who’s at higher risk: Athletes who eat little or no meat, fish, or dairy. Very selective eaters. Teens with any digestive issues that could affect absorption. If your kid falls into any of those categories, B12 is worth paying attention to.

3. Folate: The One Nobody Talks About

Folate doesn’t get the headlines that vitamin D or iron do, but it’s quietly essential; especially for teen athletes whose bodies are simultaneously growing and recovering from high training loads. It supports cell growth and red blood cell production, which means it’s doing double duty during growth spurts.

What it looks like when it’s low:

•   Getting gassed earlier than teammates during conditioning

•   Bounce-back after hard sessions takes noticeably longer

•   A pattern of fading mid-week: strong Monday, rough Thursday

The tricky thing about folate is that it’s abundant in healthy foods (leafy greens, lentils, beans, citrus, avocado) but “abundant in healthy foods” and “actually consumed by a 15-year-old” are two very different things.

4. Vitamin B6: The Training Adaptation Nutrient

B6 is the behind-the-scenes player in protein metabolism and energy pathways. Think of it as the nutrient that helps your teen’s body actually use the training they’re putting in. Without enough of it, the work goes in but the adaptation doesn’t come out the other side.

Subtle warning signs:

•   Sleep that’s consistently “off”: trouble falling asleep, waking during the night, or waking unrested

•   Soreness that seems disproportionate to the workload

•   Mood instability during heavy training blocks (more than just normal teenage hormones)

Good dietary sources include poultry, fish, potatoes, bananas, and chickpeas. But like many B vitamins, B6 is water-soluble, meaning the body doesn’t store it efficiently, and heavy training accelerates the need.

5. Vitamin D: The One Almost Everyone Is Low On

Vitamin D is probably the most widely discussed nutrient deficiency, and for good reason. It supports bone health, muscle function, and immune resilience, all of which directly affect whether your teen can stay on the field consistently. The problem is that most teen athletes don’t get nearly enough of it, especially if they train indoors or live in northern climates.

Red flags:

•   Recurring off-weeks with vague complaints: low energy, nagging aches, general “blah”

•   More time lost to minor injuries (stress reactions, slow-healing strains)

•   A noticeable dip in energy and motivation during fall and winter months

Who’s most at risk: Indoor sport athletes (swimmers, gymnasts, volleyball, basketball), teens who train before school or after dark, and anyone in a region where winter means limited sun exposure for months at a time. Fatty fish, fortified dairy, and egg yolks help, but sun exposure is the primary driver, and most teens simply aren’t getting enough.

Why a Multivitamin Isn’t the Answer (Even Though It Feels Like It Should Be)

Here’s where most parents land: “Okay, they might be low on something. I’ll grab a multivitamin.” It makes sense. It’s easy. And it’s not exactly wrong. A quality multivitamin is a fine safety net. But for a competitive teen athlete, it’s a blunt instrument for a precision problem.

Here’s why:

It doesn’t tell you what’s actually low. A multivitamin assumes everything needs a boost. But your teen might be fine on vitamin C and critically low on magnesium. Without data, you’re guessing, and guessing means you’re probably over-supplementing in some areas and under-supplementing in others.

The doses aren’t built for athletes. Generic formulas are designed for the general population, not a 16-year-old who’s training 10 to 15 hours a week and growing two inches a year. Training load, growth rate, diet, and absorption all vary wildly from one teen to the next.

Consistency is a real challenge. Between school, travel, tournaments, and the general chaos of adolescence, a daily multivitamin habit is hard to maintain. And a supplement you take three days out of seven isn’t doing much.

The smarter move isn’t to throw everything at the wall and hope something sticks. It’s to find out what’s actually going on, and then make targeted changes that matter.

Stop Guessing. Start Testing.

If any of this sounds familiar, if your teen is doing the work but not seeing the results, if mid-week crashes are becoming the norm, if you’ve tried everything and something still feels off, it might be time to look under the hood.

MD Perform’s Precision Nutrient Testing Kit gives you a clear, data-driven picture of what’s happening inside your teen’s body. The kit ships to your door with everything needed for at-home collection and a prepaid return mailer. Once results are in, you’ll get detailed nutrient insights delivered to your inbox, plus full access to the MD Perform Member Portal with step-by-step videos, educational resources, and practical guidance to help you turn the numbers into real changes that fit your family’s life.

The best thing you can do for your teen athlete isn’t more training, it’s making sure the training they’re already doing actually counts.

→ Order the MD Perform Precision Nutrient Testing Kit

 

This article is for general educational purposes only. MD Perform provides testing insights and educational resources only. Use of this site and/or the purchase of a testing kit does not establish a doctor-patient relationship between you (or your child) and MD Perform or Dr. Amy Biondich. Always consult a licensed healthcare professional for medical concerns.