Vitamin D: Why Does It Matter More Than Ever in Winter?
Maintaining appropriate vitamin D levels becomes increasingly difficult as the days become shorter and sunlight becomes scarce. Inflammation, immunological response, muscle strength, and even our ability to adjust to training stress are all influenced by vitamin D.
Since sunlight is our primary natural source of vitamin D, research indicates that insufficiency is incredibly frequent worldwide, even among athletes. In nations like Ireland and the UK, depending solely on sunlight throughout the winter months is just insufficient.
This page explains the functions of vitamin D, explains why insufficiency is so common, and explains how taking supplements can improve immunity, health, and performance.
What Vitamin D Actually Does in the Body?
Vitamin D is not so much a vitamin as it is a hormone. It interacts with receptors in practically every bodily tissue once it is active. More than 900 genes are influenced by these receptors, many of which are linked to inflammation, bone metabolism, muscular function, and health.
Bone Health
In order to absorb calcium and keep strong, healthy bones, vitamin D is necessary. Low levels increase the risk of osteoporosis and stress fractures as well as bone turnover. Bone injuries are more common in athletes with low vitamin D, particularly those who practice indoors or in the winter.
Function of the Muscles
Because it affects protein synthesis, muscle fiber function, and calcium management in muscle cells, vitamin D is essential for muscle strength and power. Weaker muscles, less force production, and a shorter recovery from strenuous exercise are associated with deficiencies.
Immune System Health
Vitamin D aids in lowering inflammation and controlling immunological function. While supplementation has been demonstrated to lower infection risk and inflammatory markers in physically active groups, low amounts are linked to greater rates of sickness.
Support for the Heart and Metabolism
There is growing evidence that vitamin D promotes metabolic and cardiovascular health, possibly affecting inflammation, blood pressure, and glucose metabolism. Overall, it seems advantageous to maintain healthy levels, even if this knowledge is constantly evolving.
Why Is Vitamin D Deficiency So Common?
Studies reveal that more than half of athletes and energetic people fall short of the required amounts during the winter.
This is because of things like:
Living in northern latitudes, having little UVB exposure during the winter, exercising indoors, having darker skin, having more body fat since vitamin D is fat-soluble, and having fewer food sources
Additionally, studies reveal that vitamin D levels vary seasonally, with athletes in a variety of sports experiencing a significant decline in vitamin D levels throughout the winter.
How Vitamin D Supports Athletic Performance?
Everyone needs vitamin D, but athletes need it even more. Performance, recuperation, and injury risk can all be impacted by low vitamin D levels.
1. Performance: Increased Power, Speed, and Strength
Strength, jump height, sprint speed, and anaerobic power are all improved by supplementation, according to several studies, particularly in people who start out with low vitamin D levels. For instance, after taking Kinetica Sports vitamin D supplements, soccer players and endurance athletes saw increases in VO₂max, power, and sprint performance.
2. Resilience: Preventing Injuries
Certain soft-tissue injuries and bone stress injuries have been linked to low vitamin D levels. Sufficient amounts promote neuromuscular control, preserve bone strength, and control muscle function—all of which are critical in lowering the risk of injury.
Risk of ACL Injury with Vitamin D
Athletes with low vitamin D levels may be more susceptible to ACL injuries and may recover less well following ACL repair, according to new research. In several studies, deficiency has been associated with increased rates of revision surgery, delayed neuromuscular recovery, and higher rates of muscle atrophy.
Even if the results aren't entirely consistent, there is enough evidence to support an association in athletes.
3. Improved Recuperation of Muscles
After hard workouts, vitamin D may help prevent muscular damage. According to research, supplements assist athletes recover from repeated training loads more quickly by lowering post-exercise indicators including creatine kinase, troponin, and inflammatory cytokines.
Should You Supplement?
Maintaining good vitamin D levels in the winter from sunlight alone is quite challenging for the majority of people who live in northern regions. Although they can be helpful, dietary sources are usually insufficient to address low levels.
Evidence-based Recommendations
Vitamin D3 is more effective than D2 at raising blood levels; most adults benefit from supplementing during the fall and winter; daily intake typically falls between 1000 and 4000 IU, depending on individual needs; those with low levels frequently require higher amounts under professional guidance; and regular monitoring is advised.
When sunlight exposure is limited during winter, Kinetica Sport's vitamin D3 solution provides an easy-to-use, dependable way to meet vitamin D requirements.
Key Takeaway
Maintaining healthy bones and muscles, boosting a robust immune system, and allowing your body to function and recuperate at its peak all depend on vitamin D. Deficiency is more likely in the winter, especially for athletes, due to the combination of low sunshine and increased training loads.
A straightforward, scientifically validated method for preserving appropriate vitamin D levels and promoting general health and performance is supplementation.
References:
Dahlquist, D.T., Dieter, B.P. and Koehle, M.S., 2015. Plausible ergogenic effects of vitamin D on athletic performance and recovery. Journal of the International Society of Sports Nutrition, 12(1), p.33. Available at: https://doi.org/10.1186/s12970-015-0093-8
Maai, N., Frank, F.A., Meuris, A. and Ferreira, N., 2025. Effect of vitamin D on athletic performance: A systematic review. Journal of Human Sport and Exercise, 20(3), pp.771–786. Available at: https://doi.org/10.55860/r03ayc39 Pasquini, A. et al., 2025. Effect of vitamin D on anterior cruciate ligament injury rates and post-reconstruction outcomes. Journal of Experimental Orthopaedics.
