It shouldn’t come as a surprise that consuming a healthy diet rich in lean proteins, healthy fats, and complex carbs is key to optimizing body function and athletic performance. But even if you’re consuming a healthy and balanced diet, you could be deficient in certain nutrients.

Whether it’s from stress, poor sleep, dietary restrictions, or medications, nutrient levels can easily become depleted. If you’re not replacing them, your risk of deficiency greatly increases and can lead to negative effects on your everyday performance.

Right now, we’re talking about two key nutrients that often run low: vitamin D and vitamin B12. We’re exploring the benefits of both nutrients and how they work together to enhance exercise performance.

The Details On Vitamin D For Health

Sometimes referred to as the sunshine vitamin, vitamin D is a major fat-soluble pro-hormone whose importance has been gaining a fair bit of attention.

The vitamin D receptor (VDR) is part of the steroid hormone receptors responsible for inducing a cascade of cell signaling to maintain normal calcium levels that are key for regulating several biological functions 1.

Virtually all cells and tissues of the body contain vitamin D receptors (VDRs), which suggests that vitamin D is involved in roles beyond its classic action on bone metabolism.

There are few vitamins that the body can synthesize de novo, but vitamin D is one. When the skin is exposed to sunlight, UVB rays convert the sterol 7-dehydrocholesterol to a form of vitamin D called cholecalciferol 2. Eventually, vitamin D is converted to its active form, 25-hydroxycholecalciferol (25(OH)D3).

Vitamin D3 is known to play several important roles in:

  • Immune function
  • Bone health
  • Mood
  • Cognitive function
  • Blood sugar regulation
  • Inflammation

But because of its role in calcium metabolism and bone health, it’s suggested that vitamin D may also have links to exercise performance.

An older study published in 1988 found that blood levels of Gla-protein, an indicator of bone formation, and vitamin D were higher in resistance-trained individuals. These results may be because strength training aids osteoblastic bone forming ability, and vitamin D provides calcium for newly forming muscle tissue 2.

Other studies show that optimal plasma concentrations of vitamin D help suppress the inflammatory cascade that accompanies physical activity by maintaining levels of pro and anti-inflammatory cytokines (specifically TNF-α, and interleukin-10) 3.

Not only that, but vitamin D may also enhance muscle protein synthesis by activating intracellular receptors, promoting muscle strength, mass, and endurance by maintaining sufficient ATP, and reducing DOMS 4.

Breaking Down Vitamin B12

The classic action of vitamin B12 is in the formation and function of red blood cells, but research suggests that the role of vitamin B12 may extend beyond that of erythropoiesis to include protein, fat, and carbohydrate metabolism 2.

Vitamin B12 belongs to the group of water-soluble vitamins that function as important coenzymes and cofactors for numerous biological reactions. It plays an essential role in the development, myelination, and function of the central nervous system, the formation of healthy red blood cells, and DNA synthesis 5-7.

Vitamin B12 also functions as a cofactor for two enzymes: methionine synthase and L-methylmalonyl-CoA mutase.

The former is required for the conversion of homocysteine to methionine, whereas the latter helps convert L-methylmalonyl-CoA to succinyl-CoA in the metabolism of the short-chain fatty acid propionate 8. And along with folate (vitamin B9), B12 produces S-adenosylmethionine (SAMe), a compound that is involved in regulating mood and immune function.

However, here’s the thing with vitamin B12.

Unless you’re a vegan, chances are you’re getting enough B12 through diet. But for your body to actually absorb B12, it must bind to a protein called intrinsic factor to be absorbed. Since intrinsic factor is activated by stomach acid, you need sufficient acid levels to truly absorb any B12 you consume.

That’s where supplementation can be really useful, as sublingual B12 can bypass gastric absorption.

Regardless, maintaining sufficient levels of B12—along with vitamin D—is critical to supporting optimal body function, but what can they do for your athletic performance.

3 Benefits of Vitamin D and B12 for Exercise

When it comes to exercise, vitamins and minerals are essential for energy production and thus serve as an easy way to optimize exercise performance. But for anyone engaging in rigorous or prolonged physical activity, vitamin requirements may increase as nutrients are lost through sweat.

However, while some studies have shown that nutrient loss during exercise is negligible unless training in hot environments, supplementing to top up your levels may prove beneficial in some capacity.

Here’s why.

Reduces fatigue

The B vitamins play a major role in the body’s energy production pathways and a deficiency of any one can interfere with energy levels.

That’s partially why one of the most common symptoms of anemia is fatigue. Red blood cells aren’t saturated with oxygen and therefore tissues aren’t being properly oxygenated. As a result, they don’t function optimally and you feel tired and weak.

As well, thiamine and biotin/vitamin B12 all play roles in the mitochondrial metabolism of glucose, fatty acids, and amino acids, respectively, and contribute substrates to the citric acid cycle—a major part of the production of ATP, your body’s main source of energy 9.

If that’s not enough, B12 is also needed for the folate cycle to function properly. This cycle synthesizes and regenerates tetrahydrobiopterin, an important cofactor to convert amino acids to neurotransmitters (serotonin, melatonin, dopamine, noradrenaline, adrenaline), and nitric oxide 9.

Low vitamin D, on the other hand, has been linked to higher perceived ratings of fatigue, along with headaches, musculoskeletal pain and weakness, mood changes, and impaired cognitive performance 10.

While the way vitamin D reduces fatigue isn’t completely clear, we do know that vitamin D receptors (VDR) are present in several areas of the brain.

Central fatigue is suggested to arise from a dopamine imbalance, and VDR have been found in dopaminergic neurons, which means they're modulated by vitamin D 10. Additionally, vitamin D may function as a key regulator of brain serotonin synthesis and dysfunctional serotonergic function may contribute to fatigue.

Improves exercise recovery

While all the B vitamins are essential for performance and recovery, B6, B9 (folate), and B12 are arguably the most important.

Both B6 and B12 have direct roles in protein metabolism and are essential for the formation of red blood cells and proper immune function. Sufficient folate, B6, and B12 are also needed for the conversion of homocysteine to methionine, which improves nitric oxide production and endothelial function.

All of this means better tissue oxygenation, better blood flow, and better muscle performance.

Vitamin D is also arguably one of the most essential nutrients for supporting recovery because of its role in maintaining the health of skeletal muscle and bone.

There’s increasing evidence suggesting that vitamin D is involved in muscle damage and regeneration 11. Studies show that vitamin D can mitigate reactive oxygen species (ROS) production, support antioxidant defenses, and prevent oxidative stress, a common factor involved in muscle damage.

What’s more, VDR knockdown causes reduced mitochondrial oxidative capacity and ATP production, which interferes with muscle regeneration.

And that’s not it.

Studies also suggest a strong link between sufficient levels of vitamin D and optimal muscle function 12. Higher levels of vitamin D help to reduce inflammation, pain, and myopathy while at the same time increasing muscle protein synthesis, ATP concentration, strength, jump height, velocity, power, exercise capacity, and physical performance.

Boosts cardiovascular and cardiorespiratory performance

The health of the cardiovascular system is of the utmost importance for athletes and research suggests that vitamin D and vitamin B12 are key to maintaining optimal cardiovascular performance.

B12 plays a direct role in the conversion of homocysteine to methionine. A deficiency of B12 results in the accumulation of homocysteine and increases the risk of several diseases, including hypertension, diabetes, atherosclerosis, renal and cardiac failure, and neurodegeneration 13.

While there are several mechanisms for elevated homocysteine causing endothelial dysfunction, one of the major ones is inhibition of nitric oxide (NO); NO is an important vasodilator that helps to enhance blood flow and oxygen and nutrient delivery to active tissues.

Cardiovascular fitness is a direct indicator of physiologic status. It reflects the cardiovascular and respiratory systems' ability to prolong vigorous exercise.

Based on this, any disruption to peripheral tissue, related vasculatures, coronary arteries, or the heart would decrease cardiovascular fitness and impair exercise performance.

As such, keeping your B12 levels up to support the proper conversion of homocysteine to methionine becomes critical for supporting endothelial health and cardiovascular performance.

That’s not all. Vitamin D appears to also have benefits for cardiorespiratory fitness.

A study published in the European Journal of Preventive Cardiology found that higher levels of vitamin D are linked to greater exercise abilities 14. Researchers looked at more than 2,000 people who were divided into quartiles based on their vitamin D levels.

They found that cardiorespiratory fitness for people in the top quarter was 4.3 times higher than people in the bottom quartile, and even after adjusting for external factors (age, race, BMI, etc.), they were still 2.9 times higher. Each 10-point increase in serum vitamin D levels resulted in a 0.78-point increase in V02 max.

Simply put, a better VO2max means a great ability to exercise at a more vigorous intensity for longer.

Final Thoughts

With all of that said, maintaining normal levels of both B12 and vitamin D is crucial for overall health and well-being.

But if you want to enhance exercise performance, dosing up on both should be a top priority to support energy levels, cardiovascular and cardiorespiratory performance, and accelerate muscle recovery.


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