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Quick guide: Vitamin D supplementation for building lean muscle

Vitamin D. The sunshine vitamin. It’s most commonly known for its role in increasing the absorption of calcium and other minerals from your intestine. Now, we know it is involved in so much more.

Vitamin D has been repeatedly linked to skeletal muscle functioning. This link is making everyone question its role in maintaining healthy muscle. Where is the research at? Should you add vitamin D to your supplement repertoire?

This week’s article will answer these questions and more. I’ll take you through what vitamin D is, how it works, what the evidence is linking vitamin D to muscle health, and how much you need to supplement with.

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What is Vitamin D?

Vitamin D, also known as cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2), is a fat-soluble essential vitamin. That means vitamin D can dissolve in fats and oils, can be absorbed along with fats in the diet, and it can be stored in the body’s fatty tissue.

An essential vitamin is one our body cannot create on its own and must be obtained from an outside source.

Vitamin D has many different biological functions: it is an antioxidant, immune-booster, linked to maintaining optimal levels of testosterone, increases cognition, promotes bone health, and improves general well-being.

The main source of vitamin D is from the sun, although it is also found in fish, eggs, and many dairy products (because it is added artificially to dairy afterwards). The body generates vitamin D from cholesterol in the presence of enough UVB light from the sun.

How vitamin D works

Vitamin D from the diet or synthesized from the skin is initially inactive. Each of these sources (diet or skin) has a slightly different path to activation.

Vitamin D lies dormant in the skin until it is exposed to UVB light. It then breaks apart into a molecule called pre-vitamin D3. From there, it travels to the liver where it is converted to hydroxycholecalciferol and then on to the kidney where it finally becomes 1,25-dihydroxycholecalciferol (the active form of vitamin D3).

The active form can then travel to various parts of the body and exert its effects via a receptor (the vitamin D receptor) expressed in the nucleus of cells.

Orally ingested vitamin D3 skips the initial step that takes place in the skin and goes straight to the liver and kidney for conversion into its active form.

The mechanism of action of vitamin D makes it very similar to a hormone.

Vitamin D and muscle health

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Vitamin D is associated with increased strength, better aerobic fitness, and improved muscle function. It is linked to muscle tissue via neuromuscular adaptation, protein synthesis, and fat infiltration into muscle tissue.

The term, “neuromuscular”, refers to the interaction between your nerves and voluntary muscles. These interactions affect things like muscle strength and power. Low serum vitamin D levels in humans are associated with decreased strength and increased weakness. The converse is also true. Higher serum vitamin D is linked to greater muscle strength in both men and women.

Research suggests vitamin D supplementation can improve rates of protein synthesis. A group of scientists in France compared protein synthesis rates of old rats (who have age-related protein synthesis deficiencies) introduced to a diet high in vitamin D and low vitamin D.

The rats who ate the diet high in vitamin D had much higher muscle protein synthesis rates compared to the rats who did not.

Ever seen a marbled steak? That’s what fat infiltration looks like in muscle tissue. Vitamin D deficiency is linked to increased fat infiltration in muscle, according to research published in the Journal of Clinical Endocrinology and Metabolism. Less vitamin D means more fat in the muscle, which affects muscle strength and power generation.

Vitamin D deficiency

Much of the general population does not get enough vitamin D. There are 4 possible states when vitamin D levels are measured in blood serum.

  1. Deficient – less than 12ng/ml
  2. Insufficient – between 12 and 20ng/ml
  3. Adequate – between 20-50ng/ml
  4. High – more than 50ng/ml

**ng/ml = nanograms per milliliter

The only way to know your vitamin D status definitively is to get your blood tested. Some common symptoms of vitamin D deficiency are bone pain and muscle weakness. If you’re noticing these symptoms, it may be worth your time to make an appointment to get your blood checked.

How to supplement with Vitamin D

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Vitamin D’s recommended daily allowance is 400-800 IU per day, which is way too low.

Research suggests vitamin D is safe taken up to 10,000 IU per day. If you’re looking to start supplementing, a good amount to go with is 1,000 to 2,000 IU per day. This will meet the needs of a vast majority of the population, be enough to confer the general health benefits of vitamin D, and will also be enough to let you experience the beneficial effects of vitamin D for muscle health.

Vitamin D3 or D2?

Vitamin D3. It’s used more effectively in the body. And take it daily with meals or a source of fat. Vitamin D is fat-soluble so this will help its absorption from the intestine.

Vitamin D is considered safe when taken in the recommended amounts (compare the recommended dose with the upper limit above). If you do go overboard, some common side-effects include weakness, fatigue, sleepiness, headache, loss of appetite, dry mouth, metallic taste, nausea, and vomiting. But this will not happen if you stick to the recommended doses.

There are some people who should avoid vitamin D supplements.

Because vitamin D increases calcium levels in the blood, it should be avoided by people with kidney disease (can cause hardening of the arteries), who already have high calcium levels, sarcoidosis, histoplasmosis, an overactive parathyroid gland, lymphoma, or tuberculosis.


Because of its safety and link to general health benefits and muscle maintenance and performance, adding vitamin D to your supplement repertoire is a good idea. There’s lots to gain and little risk associated.

If you’d like more information on vitamin D supplementation, contact me. I’d love to help you out.

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Have a great week!



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