Optimizing Vitamin D for Health and Wellness

Vitamin D is a fat-soluble prohormone essential to the health and function of nearly every system in the body. While it’s best known for regulating calcium and maintaining bone density, vitamin D also plays a direct role in muscle strength, pelvic floor function, immune response, metabolic health, and hormonal balance. Despite Arizona’s abundant sunshine, vitamin D deficiency remains common, often due to indoor lifestyles, consistent sunscreen use, higher melanin levels, and age-related changes in synthesis and metabolism. At the Performance Medicine Institute, we routinely evaluate and optimize vitamin D levels as part of our comprehensive approach to musculoskeletal and metabolic care.

Where Vitamin D Comes From

Vitamin D exists in two primary forms, D2 (ergocalciferol) from plant sources and fortified foods, and D3 (cholecalciferol), which is synthesized in the skin through UV light exposure or obtained through animal-based foods. Once in the body, vitamin D3 is converted in the liver to 25-hydroxyvitamin D, the major circulating form, and then further activated in the kidneys to 1,25-dihydroxyvitamin D (calcitriol), the biologically active hormone. This final form binds to vitamin D receptors (VDRs) located in tissues throughout the body, regulating gene expression and cellular function.

Vitamin D and Muscle Strength

Skeletal muscle expresses vitamin D receptors, and vitamin D directly impacts muscle function through calcium signaling, mitochondrial energetics, and activation of anabolic pathways. Deficiency in vitamin D has been linked to fatigue, poor exercise recovery, reduced contractile strength, and increased fall risk in older adults. Correcting low levels has been shown to improve muscle strength, particularly in the lower body, as well as enhance neuromuscular coordination and power output during training. In athletic populations, adequate vitamin D is associated with better performance and fewer injuries.

Bone Health and Calcium Regulation

Vitamin D is essential for calcium absorption in the gut, helping maintain serum calcium levels and ensuring proper mineralization of bone. Chronic deficiency leads to demineralization, impaired remodeling, and increased fracture risk. In adults, this can manifest as osteomalacia or contribute to osteoporosis. In younger athletes, low vitamin D status has been associated with higher rates of stress fractures. Optimizing vitamin D supports both bone density and skeletal resilience across the lifespan.

Pelvic Health and Neuromuscular Function

The pelvic floor, like other skeletal muscle systems, is influenced by vitamin D through its effects on neuromuscular coordination, inflammation, and tissue regeneration. Research increasingly shows a link between low vitamin D levels and pelvic floor dysfunction, including urinary incontinence, overactive bladder, and pelvic pain syndromes. These effects are particularly prominent as we get older, and may be compounded by hormonal changes or sarcopenia.

Systemic Health and Hormonal Support

Vitamin D’s influence extends far beyond the musculoskeletal system. Immune cells express VDRs, and optimal levels enhance innate and adaptive immunity, reduce systemic inflammation, and may help prevent respiratory tract infections. Vitamin D is also involved in hormone synthesis, including testosterone production and spermatogenesis, and may support reproductive health in men. Cognitive health, mood regulation, and neuroprotection are also influenced by vitamin D status, with low levels linked to depression, anxiety, and cognitive decline. Metabolically, vitamin D is associated with better insulin sensitivity and lipid profiles, suggesting a potential role in the prevention of metabolic syndrome and type 2 diabetes.

What Levels Are Optimal?

At the Performance Medicine Institute, we aim for serum 25-hydroxyvitamin D levels between 40 and 60 ng/mL. While levels above 20 ng/mL are considered “sufficient” by some guidelines, research shows that higher levels are associated with better musculoskeletal, immune, and metabolic outcomes. For individuals with mild deficiency (20-30 ng/mL), a daily dose of 2,000 to 3,000 IU of vitamin D3 is typically effective. More severe deficiencies may require short-term high-dose protocols under supervision. Maintenance dosing is customized based on lab results, body weight, fat mass, and comorbid conditions.

Vitamin D can also be too high. For levels over 80-100 ng/mL, vitamin D toxicity can occur. It is therefore important to not take too much vitamin D, and to verify levels are within optimal range.

There is emerging evidence that taking vitamin D with vitamin K2 (menaquinone-7) offers some health benefits. The literature is evolving on this point, and certainly for older individuals with osteoporosis there appears to be some clear benefits of taking vitamin K2 along with vitamin D3 to optimize bone health. However, during the initial phases of loading for vitamin D, taking vitamin K2 may not be necessary, but for maintenance doses this may be helpful. So we recommend supplementing with vitamin K2 in the maintenance phase, but it is not critical in the loading phase.

The following protocol is what we recommend for many patients with vitamin D deficiency. However, you should check with your healthcare provider before starting any treatment routine. This protocol is based on your starting level of vitamin D3 from your labs. Different individuals can metabolize vitamin D at different rates, so it is important to periodically check vitamin D levels to ensure optimal treatment dose.

If you are over 60ng/mL it is likely that your vitamin D3 is not optimal, and once it reaches 80-100 ng/mL you can start showing signs of vitamin D toxicity. If you are at this level and are not intentionally taking a vitamin D supplement, it is likely there is another supplement that you are taking which contains vitamin D.

Choosing a Vitamin D Supplement

There are numerous over the counter Vitamin D3 supplements. We recommend the Nivagen Vitamin D3 50,000 IU supplement for the loading phase and the Sports Research Vitamin D3 + K2 supplements.

Summary

Vitamin D is a foundational nutrient for strength, performance, pelvic stability, and whole-body health. It enhances muscle function, promotes bone density, regulates hormonal and immune systems, and supports neuromuscular control across multiple organ systems. Despite living in a sunny climate, vitamin D deficiency remains common and often goes unrecognized. We routinely test for and treat vitamin D deficiency to support optimal performance, recovery, and well-being. Curious about your vitamin D status? Contact us to schedule lab testing and a personalized plan to reach optimal levels for performance and health. Contact Us today to learn more about personalized treatment options.

References

Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3):266–281.

Ceglia L. Vitamin D and skeletal muscle tissue and function. Mol Aspects Med. 2008;29(6):407–414.

Parker-Autry CY, et al. Vitamin D status and pelvic floor disorders in women: A systematic review. Int Urogynecol J. 2020;31(4):711–721.

Owens DJ, et al. Vitamin D and the athlete: Current perspectives and new challenges. Sports Med. 2018;48(Suppl 1):3–16.