Optimize Your Training: Vitamin D’s Role in Muscle Building and Fat Burning
Fuel your performance - discover how optimizing your vitamin D levels can boost strength, muscle mass, and metabolic efficiency. Read the science behind this game-changing nutrient
Athletes know the essentials: protein builds muscle, sleep recovers it, and training with weights is the driver. We need to add this as new research suggests one more key player in muscular performance and it is hiding in plain sight. Vitamin D, long associated with bone health, may be a critical regulator of muscle growth, strength, and even how your body chooses to burn or store energy.
A study from the Children’s Hospital of Philadelphia uncovered that high-dose vitamin D shifts your body's energy economy: instead of storing excess calories as fat, it helps build muscle. The process works by altering two powerful hormones - leptin, which regulates appetite and energy balance, and myostatin, which limits muscle growth.
Vitamin D decreases myostatin, allowing muscle to grow, while simultaneously increasing leptin production and sensitivity, improving how the brain regulates energy expenditure. In short, your body burns more and stores less, all by design.
A Shift in Strength
In a controlled mice study, researchers found that mice on high-dose vitamin D developed greater muscle strength and lean mass without gaining weight. They also showed increased energy expenditure without increased food intake, suggesting a shift in energy allocation.
Researchers then used human genetic data to confirm that people genetically predisposed to higher vitamin D levels also tend to be taller. Clinical data showed improved growth hormone and IGF-1 levels after vitamin D dosing. Even fish embryos exposed to higher vitamin D grew longer, suggesting an evolutionary linking between vitamin D and growth and muscle development.
Muscle Meets Evidence
In 16 randomized controlled trials led by Lars Rejnmark, the impact of vitamin D supplementation on muscle function in adults was very clear. Nearly half of the studies demonstrated improved muscle strength, postural stability, and physical performance with vitamin D supplementation.
Studies demonstrated when participants started with low vitamin D levels and supplemented with Vitamin D the benefits were substantial. For example, trials showed improved quadriceps strength, better balance (reduced body sway), and faster performance on standardized physical testing. It is worth noting that the effects were inconsistent across all trials, but this could be likely due to varying study designs, populations, and dosages. One of the most notable improvements was in grip strength with supplementing with Vitamin D suggesting its effects extend beyond just muscles but effects the CNS.
The Rejnmark review also highlighted that vitamin D deficiency contributes to proximal myopathy. An issue effecting older adults where weakness in large muscle groups used for climbing stairs or standing from a chair are prominent. These issues many times emerge before signs of bone disease, meaning vitamin D deficiency could silently impair athletic performance long before it's detected by conventional medical testing.
A New Model of Strength
An updated theory on Vitamin D supplementation is going deeper than just muscle strength. For years, the model of energy storage was seen as binary: burn or store. But this new research proposes a “energy balance sensing” model, where vitamin D helps the body anticipate energy needs and distribute calories accordingly to grow, potentially build muscle and effect fat storage.
It is pretty simple if you think about it - in winter, when vitamin D levels drop due to less sun exposure, the body stores more fat. In summer, more sunlight means higher vitamin D, which allows the body more add more lean mass. This could explain seasonal variations in human performance and may even inform how we time supplementation for peak training performance.
In hindsight, if had understood the role of Vitamin D and sun exposure during my NFL playing days in Philadelphia, Kansas City and New England, I would have added red light exposure mixed with Vitamin D supplementation as a way to combat seasonal depression and the loss of lean body mass I experienced over the course of the season. Once it got cold and dreary on the Eastern Seaboard and Midwest it was a hard fight to keep muscle over the many months of an NFL season. I always chalked it up to the grind of an NFL season but after reading the research in preparation for this article, I am regretting not getting my Vitamin D levels checked periodically through the year as a way to starve off the natural decline in muscle I would see over the course of an NFL season.
What This Means for Athletes
If you’re aiming to build muscle, improve metabolic efficiency, or optimize performance, vitamin D may be just as crucial as protein or creatine. Yet, many people, especially in winter or with limited sun exposure like I experienced living on the east coast and Midwest have less than optimal vitamin D levels.
I would recommend getting your Vitamin D levels tested by your doctor, or from a company like Thorne which offers testing and supplements. Once you have a baseline, you can work with a professional to supplement accordingly to maximize your Vitamin D levels.
Bottom Line
Vitamin D is a key regulator of how your body is using calories to grow. There is growing evidence from genetic studies, animal research, and human trials, to support vitamin D’s role in performance enhancement. So if you want to get on the gain train, make sure you are getting regular sunshine and maximizing your Vitamin D.