Less sunlight in fall and winter means your body produces less vitamin D naturally—and that can have a real impact on your training. Vitamin D plays a role in bone strength, muscle activation, immunity, inflammation, and even mood. But most athletes don’t get enough during the darker months, especially if they train indoors or live at northern latitudes.
While food alone may not provide sufficient levels, there are natural dietary sources worth including.
A few foods that are naturally rich in vitamin D include:
-
Fatty fish like salmon and sardines
- Egg yolks
- Fortified milk or yogurt
-
Mushrooms exposed to UV light
In this article, we’ll break down what vitamin D actually does for athletes, why it’s harder to get enough in the winter, and how to know if you should supplement.
What Vitamin D Does for Athletes
Supports Calcium Absorption and Bone Strength
Vitamin D helps your body absorb calcium—which is important for bone formation and density. For athletes, especially those engaged in high-impact sports, this is important as it reduces the risk of stress fractures. Vitamin D supplementation also helps maintain healthier bone turnover, reducing the risk of bone breakdown and stress injuries.
Supports Muscle Activation and Function
Vitamin D plays a role in muscle contraction, energy production, and performance. It helps your muscle cells produce energy efficiently by supporting mitochondrial function. Deficiency can cause early muscle weakness—even before blood tests show it.
Improves Muscle Recovery and Reduces Muscle Injury
Vitamin D may aid in muscle regeneration following intense training or injury. In one study, higher vitamin D levels were linked to faster muscle recovery and reduced damage post-injury, while another found that NFL players with lower vitamin D levels were more likely to suffer muscle injuries.
Supports Immune Health and Reduces Inflammation
Vitamin D supports immunity and helps lower inflammation by reducing pro-inflammatory cytokine activity, which supports overall immune resilience—especially in athletes under heavy training loads.
May Aid Recovery Through Cell Repair and Mood Regulation
Vitamin D supports tissue repair after hard training and plays a role in serotonin regulation—helping prevent dips in motivation and mood during darker months.
Why It’s Harder to Get Enough in Darker Months
Vitamin D is one of the few nutrients your body can produce on its own—but it requires skin exposure to UVB rays from sunlight. As the sun drops lower in the sky—like in winter or late afternoon—its rays must pass through more atmosphere, which filters out most of the UVB light your skin needs for vitamin D synthesis. Combine that with shorter days, more indoor training, and heavier clothing, and you’ve got the perfect storm for low vitamin D levels.
Food sources help, but even the richest ones—like fatty fish and fortified dairy—rarely provide enough to meet athletic demands. Without supplementation or regular sun exposure, most athletes experience seasonal declines.
Are You Getting Enough? Signs You May Be Low
Research shows over 50% of athletes may be vitamin D deficient—much higher than the general population. That’s partly because training itself increases the body’s use of vitamin D. Exercise stimulates vitamin D metabolism, drawing from stores in muscle and fat, and increasing excretion. This means even outdoor athletes can be at risk, especially in the winter.
Common signs and symptoms associated with deficiency include:
- Frequent illness or infections
- Low energy or chronic fatigue
- Muscle weakness or cramps
- Joint pain or bone soreness
- Slower recovery from workouts
- Mood swings or signs of depression (especially in winter)
Athletes are particularly vulnerable due to intense exercise increasing the body's demand for vitamin D. Research shows that exercise accelerates the use and breakdown of stored vitamin D in muscle and fat tissue, potentially depleting reserves even in athletes who train outdoors or get adequate sun exposure.
Other risk factors for deficiency include:
- Training indoors or living at northern latitudes
- Having darker skin (less UVB absorption through skin)
- High training volume (increased vitamin D turnover)
- Low dietary intake of vitamin D (e.g., not eating fatty fish or fortified foods)
- Being female with low energy availability or irregular menstruation
- History of stress fractures or bone injuries
- Lean or low body fat (fewer storage sites for vitamin D)
- Collegiate or elite athletes with restricted eating schedules
Supporting your vitamin D intake year-round—especially in fall and winter—may reduce injury risk, improve immunity, and support bone and muscle recovery.
Add Vitamin D to Your Stack This Winter
Most athletes would benefit from some form of vitamin D supplementation in fall and winter months. It’s a low-risk, high-reward strategy that supports training, recovery, and long-term health.
Blonyx Multivit+ includes a daily dose of vitamin D—along with other athlete-relevant nutrients like magnesium and zinc—that are often depleted with intense training. It’s an easy addition to your existing supplement stack and works synergistically with recovery-supporting products like HMB+ Creatine or Egg White Protein Isolate.
You can add it directly to your training routine or use our bundle builder to customize a stack based on your current training focus.
Key Takeaways
Vitamin D may not be flashy, but it's foundational—especially when you’re getting less sunlight.
- Vitamin D supports immunity, muscle activation, bone health, and mood regulation—all essential for athletic performance and recovery.
- Athletes are more likely to be deficient—especially in fall/winter, when sun exposure drops and training demands stay high.
- Warning signs include fatigue, frequent illness, soreness, and slower recovery—but some may show no symptoms at all.
- Exercise increases vitamin D utilization and excretion, making dietary intake and supplementation more important.
- Vitamin D likely doesn’t improve strength or hypertrophy unless you’re deficient, but is still critical for recovery and bone health.
- You can get vitamin D from food, but most athletes need more—consider a smart, real-food-based supplement like Blonyx Multivit+.
- Now is the time to assess your vitamin D intake—before winter hits
If you learned something new and are curious to know more, head over to the Blonyx Blog or our growing list of weekly research summaries where we help you further improve your athletic performance by keeping you up to date on the latest findings from the world of sports science.
– Train hard!
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