Why Masters Athletes Are at High Risk for Vitamin D Deficiency (And Why It Matters More Than You Think)

You're doing everything right. Training consistently. Eating well. Getting your sleep.

But something feels off.

Maybe you're more tired than usual, even when your training volume is reasonable. Maybe that cold you picked up a month ago still hasn't fully cleared. Maybe your legs feel heavy, or you're noticing more aches and pains than you used to.

If you're over 40 and this sounds familiar, especially during fall or winter, there's a good chance your vitamin D levels are low.

Here's what most athletes don't realize: vitamin D deficiency is incredibly common in endurance athletes. And if you're a masters athlete, particularly if you're female or navigating perimenopause or postmenopause, your risk is even higher.

Let's talk about why this happens, what it does to your performance and health, and what you can actually do about it.

Why Masters Athletes Are at Especially High Risk

Vitamin D deficiency is a widespread problem in endurance sports. Studies show that up to 56% of athletes have insufficient levels. But that number climbs significantly in athletes over 40.

Why? As we age, our skin becomes less efficient at producing vitamin D from sunlight. A 70-year-old produces about 25% less vitamin D than a 20-year-old from the same sun exposure. If you're in your 40s, 50s, or 60s, you're already starting from a disadvantaged position.

Add to that the training patterns most of us follow: early morning or evening sessions when UVB intensity is low, sunscreen and protective clothing (smart for skin cancer prevention, terrible for vitamin D production), and indoor training during winter months.

For women, the risk increases further during perimenopause and postmenopause. Declining estrogen affects how the body processes and uses vitamin D, and the drop in bone density that comes with menopause makes adequate vitamin D levels even more critical.

If you're above 37° latitude (roughly San Francisco to Richmond, Virginia), your skin can't produce vitamin D from sunlight between October and March, no matter how sunny it is. The angle of the sun just isn't right.

Bottom line: if you're a masters endurance athlete, the odds are stacked against you.

What Low Vitamin D Actually Feels Like

Vitamin D deficiency doesn't always announce itself with obvious symptoms. It's more insidious than that.

You might notice:

• Persistent fatigue that doesn't match your training load
• Longer recovery times between hard sessions
• More frequent colds or infections that linger
• Muscle weakness or heaviness, even on easy days
• Aches and pains that seem to come out of nowhere
• Low mood or feeling mentally foggy, especially in winter

These symptoms are easy to dismiss. You're training hard, you're getting older, winter is tough. But these are also classic signs of insufficient vitamin D.

Beyond how you feel day-to-day, low vitamin D increases your risk of injury. Stress fractures, muscle strains, and slower healing from minor injuries all become more likely when levels are low. If you're dealing with recurring soft tissue issues or bone stress injuries, vitamin D deficiency could be a contributing factor.

Recovery takes longer. Inflammation stays elevated. Your immune system struggles. And you end up in a cycle where you're working hard but not seeing the progress you should.

The Mitochondrial Connection: Why Vitamin D Matters for Endurance Performance

Here's where it gets interesting for endurance athletes: vitamin D plays a critical role in mitochondrial function.

Your mitochondria are the powerhouses of your cells. They're what produce the energy (ATP) that fuels every pedal stroke, every stride, every swim stroke. Endurance performance depends on how well your mitochondria function.

Vitamin D influences mitochondrial health in several ways. It helps regulate mitochondrial calcium balance, which is essential for energy production. It supports mitochondrial biogenesis (the creation of new mitochondria), which is one of the key adaptations we're chasing with endurance training. And it helps protect mitochondria from oxidative stress, which accumulates during hard training.

When vitamin D levels are low, mitochondrial function suffers. That means less efficient energy production, slower recovery, and blunted training adaptations.

Think about it this way: you're putting in the work, but your cellular machinery isn't operating at full capacity. You're training on a system that's running at 80% instead of 100%.

For masters athletes, this matters even more. Mitochondrial function naturally declines with age. We're already fighting an uphill battle to maintain the number and quality of our mitochondria. Low vitamin D makes that battle harder.

Vitamin D, Testosterone, and Muscle Health

For male masters athletes, vitamin D plays an important role in testosterone production. Studies show a strong correlation between vitamin D levels and testosterone levels, particularly in men over 40.

As testosterone naturally declines with age, maintaining optimal vitamin D becomes even more critical for preserving muscle mass, strength, and recovery capacity.

For female athletes, especially those in perimenopause or postmenopause, vitamin D supports muscle protein synthesis and helps maintain lean muscle mass during hormonal transitions.

Low vitamin D can accelerate age-related muscle loss (sarcopenia), making it harder to maintain the strength and power you need for performance.

This isn't about performance enhancement. It's about maintaining the physiological foundation that allows you to train effectively as you age.

What the Research Shows: Performance Impacts of Vitamin D Deficiency

The evidence on vitamin D and athletic performance is nuanced, but several clear patterns emerge.

Studies show that athletes with vitamin D insufficiency (levels below 30 ng/mL) tend to have:

• Reduced muscle strength and power output
• Slower reaction times
• Increased inflammation markers
• Higher injury rates, particularly stress fractures
• Longer recovery times from illness and injury
• Blunted immune function

When athletes with low vitamin D levels are supplemented to bring them into the optimal range (40-50 ng/mL), many see improvements in muscle function, recovery, and overall training tolerance.

The research doesn't suggest that vitamin D is a magic performance enhancer. If your levels are already optimal, taking more won't suddenly make you faster. But if you're deficient or insufficient, addressing it can remove a significant barrier to performance and recovery.

For masters athletes, the performance impact extends beyond watts or pace. It's about staying healthy, recovering well, and being able to train consistently without getting derailed by injury or illness.

What to Do: Testing and Working With Your Doctor

The first step is simple: get tested.

Ask your doctor for a 25-hydroxyvitamin D blood test. This is the gold standard for assessing vitamin D status.

What the numbers mean:

• Deficient: Below 20 ng/mL
• Insufficient: 20-29 ng/mL
• Sufficient: 30-50 ng/mL
• Optimal for athletes: 40-50 ng/mL

Most athletes perform best when levels are in the 40-50 ng/mL range.

If your test shows you're deficient or insufficient, talk to your doctor about supplementation. There are different protocols depending on how low your levels are and how quickly you need to correct them.

Some doctors use a loading protocol (higher doses for 8-12 weeks to bring levels up quickly), followed by a maintenance dose. Others start with a moderate daily dose and retest after a few months. Your doctor will recommend the approach that makes sense for your situation.

What to look for in a supplement:

Vitamin D3 (cholecalciferol) is more effective than D2.

Choose third-party tested products:

Look for supplements that are NSF Certified for Sport or Informed Sport certified. These certifications mean the product has been tested for banned substances and contaminants. This matters for any athlete who may be subject to drug testing, but it's also a good quality marker even if you're not competing at that level.

You can verify that a supplement is not on the WADA (World Anti-Doping Agency) prohibited list by checking the label for NSF or Informed Sport certification, or by searching the product on globaldro.com.

When to take it:

With a meal that contains some fat, since vitamin D is fat-soluble.

What to pair it with:

Your doctor may also recommend vitamin K2 (which helps direct calcium to your bones rather than soft tissues) and magnesium (which supports vitamin D metabolism).

Retest and adjust:

Check your levels again after 8-12 weeks of supplementation. Once you're in the optimal range, retest 1-2 times per year. Late winter and late summer are good checkpoints.

Don't Ignore Food Sources

Supplementation is usually necessary to correct a deficiency, but food sources can help support your levels:

• Fatty fish (salmon, mackerel, sardines)
• Egg yolks
• Fortified dairy or plant milks
• UV-exposed mushrooms

These won't get you to optimal levels on their own if you're deficient, but they're a useful part of your overall nutrition strategy.

The Bottom Line

Vitamin D deficiency is one of the most common and most fixable gaps in masters athlete nutrition.

If you're over 40, training hard, and feeling like something's off, this is worth investigating. A simple blood test and a conversation with your doctor can give you clarity.

And if your levels are low, correcting them can make a real difference in how you feel, how you recover, and how well your body responds to training.

This isn't about chasing marginal gains. It's about removing a barrier that's keeping you from performing at your best.