Does Vitamin D Reprogram Your Body? Muscle Gains, Not Fat Storage

This episode explores the critical connections between Vitamin D, muscle health, and energy metabolism, emphasizing its role in muscle protein synthesis, hypertrophy, and body composition. We discuss the latest research, clinical findings, and the importance of maintaining adequate Vitamin D levels for optimal skeletal muscle function.

• Understanding Vitamin D's unique secosteroid structure
• Role of Vitamin D in muscle function and regeneration
• Impact of Vitamin D deficiency on muscle strength across all ages
• Energy allocation: Vitamin D's role in shifting calories to muscles
• Myostatin inhibition and its influence on muscle growth
• Leptin's role in energy management and Vitamin D's effects on it
• Clinical trials: Vitamin D supplementation for athletes and older adults
• Importance of monitoring Vitamin D levels, especially in winter
• Target populations for Vitamin D benefits, including athletes and older adults

https://pubmed.ncbi.nlm.nih.gov/38766160/
https://link.springer.com/article/10.1007/s11033-022-07998-7
https://pmc.ncbi.nlm.nih.gov/articles/PMC6021354/

Transcript

Speaker 0: 0:00

Hello everyone, Happy New Year and welcome to Season 2 and another episode of Daily Value. I'm William Wallace and today we're diving into the mechanistic and clinical connections between vitamin D and skeletal muscle. Specifically, we're going to explore its influence on muscle protein synthesis, hypertrophy, energy metabolism and body composition. Vitamin D's effects on body composition will be of special interest, given a recent publication that is in preprint in the journal Nature. This episode emphasizes current evidence, molecular pathways and what this might mean for us personally.

Speaker 0: 0:37

Vitamin D is what's known as a psychosteroid hormone. What that means is that it has a broken ring structure, which makes it different from other steroid hormones. Steroid hormones have four interconnected rings in their chemical structure, but in a secosteroid like vitamin D, one of these rings is split open. Vitamin D is an example of a secosteroid hormone because its structure has this broken ring, which is key to its unique functions in the body, such as regulating calcium levels and supporting muscle and bone health. Vitamin D is synthesized endogenously in the skin upon exposure to ultraviolet B, otherwise known as UVB radiation, or obtained exogenously through diet and supplements. Once absorbed, it undergoes hydroxylation in the liver and kidneys to become its active metabolite, 125-dihydroxyvitamin D, also known as calcitriol. This active form binds to the vitamin D receptor, which is a nuclear receptor expressed in skeletal muscle as well as all throughout the body. A nuclear receptor is a type of protein inside cells that acts like a switch to turn specific genes on or off. When activated, the vitamin D receptor complex regulates the transcription of genes critical for cell differentiation and energy metabolism. Vitamin D actually has over 2,500 genes that it regulates in one way or another through activation of the vitamin D receptor. Vitamin D receptor activation in skeletal muscle is particularly important during periods of muscle repair and regeneration.

Speaker 0: 2:13

Now, bone is the primary target for vitamin D. It accumulates up to 25% of vitamin D hours after taking a single dose of supplemental vitamin D. However, skeletal muscle takes up and releases vitamin D, making it one of the primary storage pools of vitamin D that prevents its degradation. This is likely why people with higher amounts of skeletal muscle mass can supplement with vitamin D above the average recommended amounts. That brings someone into sufficiency and still show lower blood levels of vitamin D than what you would expect from someone who is average weight and body size.

Speaker 0: 2:49

When considering the broader general population, the presence of the vitamin D receptor content in muscle tissues shows us that it has a direct influence on muscle function and regenerative capacity. A recent meta-analysis in the journal Bone Report examined the role of vitamin D in reducing muscle hypertrophy. It's particularly evident in older adults. Studies highlighted in the meta-analysis showed that severe deficiency, that's, a serum 25-hydroxy vitamin D level below 25 nanomoles per liter, which is the same as 12 nanograms per milliliter, is tied to myalgia, reduced muscle strength and a heightened risk of falls. Vitamin D levels below that threshold are routinely tied to reduced muscle strength across all age groups. Supplementation of vitamin D more consistently results in improved muscle function when baseline levels of vitamin D are in the 12 to 20 nanogram per milliliter range or under.

Speaker 0: 3:48

Vitamin D's direct and indirect effects on muscle physiology have been extensively documented in animal and cell models. One very interesting study that I mentioned earlier is in preprint in the journal Nature, meaning that it has not been officially published yet examined how high dose supplemental vitamin D actually influences energy allocation by shifting surplus calories from adipose storage towards muscle storage or muscle accretion. The findings suggest a few things One, that vitamin D deficiency could impair energy metabolism and lean tissue development. But two, that physiological seasonal variation in vitamin D may be important for controlling season-specific metabolism by affecting calorie allocation, that is, again by helping shuttle nutrients towards skeletal muscle in the summer and allocating more calories to fat in the winter. This particular study looked at the impact of high-dose vitamin D on energy partitioning and muscle growth in rodents. That's important to mention. Researchers found that when the rodents were supplemented with elevated levels of vitamin D, there was a significant shift in how their bodies actually utilized surplus calories. Instead of storing these calories as fat, the rodents allocated the energy toward muscle growth and repair. This effect was linked to two critical signaling pathways. One was myostatin inhibition.

Speaker 0: 5:15

Myostatin is a protein in the body that acts like a brake for muscle growth. It's made by muscle cells and helps regulate how much muscle you can build by telling the body to stop making more muscle. Think of it as a natural limiter that keeps muscle growth under control. In the study, vitamin D at high levels suppressed myostatin. This is interesting because past research in rodents that remove the vitamin D receptor show that the production of myostatin goes way up. To this point in time, myostatin was thought to only have homeostatic effects on muscle, but these results suggest that myostatin may have an additional role in conveying energy needs to the body centrally or at the level of the brain. In other words, the second effect that high-dose vitamin D has was on leptin modulation. Now, leptin is a hormone made by fat cells that acts like a fuel gauge for your body. It tells your brain how much energy you have stored in fat. When your fat stores are high, leptin signals your brain to reduce hunger and increase energy use.

Speaker 0: 6:17

Giving vitamin D in this study increased the amount of leptin per unit of fat mass produced, but only high-dose vitamin D resulted in improved leptin sensitivity all throughout the body. Now that was high dose In this case. I'm sure you're wondering what is high dose vitamin D? The human equivalent dose would be much higher than is recommended on a daily basis. It would be close to 50,000 international units daily. Doses that high should only be given for short periods of time and under the supervision of someone's primary health professional. Most importantly, what the study is suggesting for the first time is that vitamin D in the body may have a conserved function, whereby it helps us to distribute calories in a season-dependent manner. Think about it by altering leptin and myostatin, vitamin D historically may be helping shuttle calories to muscle in the summer, when its levels are higher, and more calories to fat in the winter, when its levels are lower. This would have been more advantageous to have more fat mass in the winter. It's also a recorded fact that humans build more muscle in the summer months, but of course general activity levels can also influence that.

Speaker 0: 7:26

Past research shows that vitamin D supports the maintenance of type 2 muscle fibers, essential for anaerobic power and strength. Experimental models with vitamin D receptor knockouts show significant reductions in type 2 fiber size and function in rodents, further emphasizing vitamin Z's role in muscle size and strength. The most documented function of vitamin D and its earliest known function is its ability to stimulate calcium uptake in the intestines. Calcium flux is needed for muscle contractility when exercising, and now we have evidence for vitamin D's downregulation of myostatin. All of these mechanisms contribute to vitamin D's effects on skeletal muscle.

Speaker 0: 8:08

So what do clinical trials show for dosing of vitamin D and muscle outcomes? Well, in athletes those with baseline serum vitamin D levels below 30 nanomoles per liter supplementation of 4,000 to 5,000 international units daily significantly improves metrics of power like vertical jump performance. That would translate to 100 to 125 micrograms. In older adults, daily supplementation of 800 to 2,000 international units has improved outcomes on functional mobility tests such as the timed up-and-go test and reduced the risk of falls. Now, on the other hand, meta-analyses indicate diminishing returns in muscle function once serum levels exceed 75 nanomoles per liter or 30 nanograms per milliliter, pointing to a threshold effect rather than a linear dose response.

Speaker 0: 9:02

Practically, prioritizing the assessment of vitamin D status can be important if someone is not supplementing with vitamin D and or not getting enough sunlight, especially in winter months and especially when living at higher latitudes. A simple 25-hydroxyvitamin D serum test can identify deficiencies, with levels above 50 nanomoles per liter or above 20 nanograms per milliliter considered adequate for skeletal muscle health. Intervention strategies should include gradual supplementation, typically in the range of 1,000 to 5,000 international units or higher daily, tailored to baseline levels. So again, that's equivalent to 25 to 125 micrograms of vitamin D daily. High-dose bolus regimens should be avoided unless clinically necessary, as studies indicate potentially adverse effects on skeletal muscle outcomes with infrequent megadoses.

Speaker 0: 10:01

Certain groups stand to benefit the most from vitamin D optimization. One is older adults. Vitamin D supplementation mitigates sarcopenia and reduces fall risk in frail populations, particularly those in institutional care. Next is athletes. Correction of deficiency enhances recovery and performance, especially in power and strength disciplines. This has been shown again with people who are deficient at baseline. Now individuals with high adiposity. Given that vitamin D is sequestered in fat stores, obese individuals require higher doses to achieve therapeutic serum concentrations. Otherwise, adipose tissue stores and holds on to vitamin D. That isn't really doing us a lot of good in the moment. Vitamin D is a cornerstone nutrient for skeletal muscle health, influencing pathways from calcium handling to energy metabolism. While its benefits are most pronounced in deficient populations, ongoing research does continue to refine dosing strategies for different purposes and different populations. Thank you everyone for joining me today on Daily Value. If you found this episode helpful or insightful, please subscribe and share it with your network. Until next time, stay healthy and have a happy new year.