Vitamin D

Why It Matters

Vitamin D is a steroid hormone essential for the development, growth, and maintenance of a healthy skeleton across the lifespan. Its primary function is to maintain calcium homeostasis. Vitamin D is synthesized from UVB rays from sunlight or obtained through diet. (source, source)

Beyond skeletal health, vitamin D regulates over 200 genes involved in immune modulation, muscle protein synthesis, and inflammatory response. It binds to the vitamin D receptor (VDR) expressed in nearly every tissue, influencing muscle fiber composition, neuromuscular coordination, and cardiovascular function. Deficiency correlates directly with increased injury rates, impaired recovery, and suppressed immune defense. (source)

Low Vitamin D: Immune and Musculoskeletal Decline

Low serum vitamin D levels stem from limited sun exposure, as the skin synthesizes vitamin D when exposed to sunlight, and inadequate conversion in the liver and kidneys. A diet lacking in foods rich in vitamin D, such as fatty fish and fortified dairy products, also contributes. (source, source)

Potential Performance Impact:

• Reduced calcium absorption, weakening bone mineral density
• Impaired muscle protein synthesis, reducing strength and power output
• Suppressed immune function, increasing illness frequency and training disruption
• Compromised neuromuscular coordination affecting movement quality

Optimization

Prioritize foods high in vitamin D: Dietary vitamin D intake increases serum 25-hydroxyvitamin D levels. (source)

Protocol: Consume at least one serving of foods high in vitamin D daily. One serving examples: Rainbow Trout (3 oz), Salmon (3 oz), Maitake Mushrooms (sliced) (1 cup), Fortified Milk (8 oz).

Get sun exposure.:UVB rays create a chemical reaction that converts 7-dehydrocholesterol in skin cells into vitamin D3. (source, source)

Protocol: Get at least 30 minutes of outdoor sunlight exposure with as much skin exposed as possible daily.

Supplement with vitamin D: Vitamin D supplementation directly increases serum 25-hydroxyvitamin D levels. (source, source)

Protocol: Supplement with at least 2,000 IU of vitamin D daily during the spring, summer, and fall months. Increase supplementation to at least 4,000 IU during the winter months.

High Vitamin D: Calcification and Toxicity Risk

Elevated serum vitamin D levels are attributed to increased exposure to sunlight, which stimulates skin synthesis, combined with excessive intake of vitamin D supplements or fortified foods. The liver and kidneys play essential roles in vitamin D activation and metabolism. (source, source)

Potential Performance Impact

• Hypercalcemia from excessive calcium absorption causing kidney stones
• Vascular calcification reducing arterial compliance
• Gastrointestinal distress including nausea and appetite loss
• Impaired kidney function from chronic calcium overload

Optimization

Limit foods high in vitamin D: Vitamin D intake increases serum vitamin D. (source)

Protocol: Monitor and limit excess consumption of foods high in vitamin D, like salmon, eggs, and red meat.

Monitor sun exposure: UVB rays convert 7-dehydrocholesterol into vitamin D3. Limiting sun exposure limits this reaction and helps reduce vitamin D levels. (source)

Protocol: Monitor excess sun exposure and ensure proper protection.

Avoid vitamin D supplementation: Vitamin D intake increases serum vitamin D. (source)

Protocol: Monitor excess vitamin D intake and supplement concentrations.