What is Vitamin D & Why Is it Important for Athletes?

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that plays a crucial role in immune health, muscle function, inflammation control, and bone strength. Many athletes, especially in the UK, are deficient, particularly during winter months.

Low vitamin D affects muscle strength, increases injury risk, and prolongs recovery.

"Although we call Vitamin D a vitamin, its active form is actually a hormone. It's a steroid hormone that is synthesised in the skin after exposure to sunlight and can also be obtained from certain foods.It supports muscle function, immune health, and bone strength – all crucial for athletic performance. Deficiency is common in athletes training indoors or during winter months. I recommend testing twice a year – ideally in spring and autumn – and addressing low levels early to reduce injury risk and support immunity. Pairing with calcium and magnesium can provide further insight into musculoskeletal health."

Dr Thom Phillips

What are normal vitamin D levels for athletes?

We looked at blood test data from EDGE customers and found that the median vitamin D level for men and women was 82 nmol/L.

Here is a breakdown of vitamin D levels by age:

Source: EDGE customer blood test results Apr 2023 – March 2025.

The labs we used to analyse blood samples state a healthy range for vitamin D is generally between 50-200 nmol/L, but we recommend levels above 75 nmol/L for optimal health and performance.

How Vitamin D Supports Performance

1. Muscle Function & Strength

   Vitamin D receptors are found in muscle tissue. Deficiency can lead to weakness and reduced power output.

2. Injury Prevention

   Adequate vitamin D supports calcium absorption and bone health, reducing the risk of fractures and stress injuries.

3. Immune Defence

   Helps maintain immune resilience during high training loads or competition.

Symptoms of Low Vitamin D

Vitamin D is essential for immune function, muscle strength, and bone health. Low levels can often present as:

• Fatigue or low mood

• Frequent illness

• Bone or joint pain

• Muscle weakness

Why Test Vitamin D?

Testing Vitamin D helps ensure your levels are optimal for performance, especially during times of limited sun exposure or increased training load. It’s important to test:

• In winter or if training mostly indoors

• When experiencing fatigue or low immunity

• To support recovery and bone integrity

In Summary

• Vitamin D underpins immunity, strength, and bone health

• Deficiency is common and often overlooked

• Testing helps guide supplementation and avoid underperformance