The Science of B Vitamins for Energy, Recovery, and Why Athletes Need More

It is generally understood that having sufficient B vitamin intake is critical for health and performance, but real attention to detail on ensuring that intake is met is still lacking. Vitamin B6, B12, and Folate (B9) are not performance enhancers in the traditional sense. Rather they are essential nutrients that allow our body to do what it needs to do, from energy metabolism to neurotransmitter production to red blood cell formation. For all three of these there is a high rate of insufficiency in athletic populations, and due to confusion around dosing and forms, many generic supplements are missing the mark. 

Here at HR Labs we included bioactive forms of B6, B12, and B9 in our WATTR™ Hydration supplement because athletes who train regularly face increased demand for these B vitamins, and the consequences of suboptimal intake can lead to problems for both health and performance.

B Vitamin Cheat Sheet

How B6, B9, and B12 Work in the Body

B6, B9, and B12 function as coenzymes, meaning they are required to allow enzymes to work properly. Without them, the reactions that convert one compound to another do not operate at full capacity, and sometimes not at all.

Each vitamin works on a host of enzymes, making for numerous functions and downstream health effects. In the following discussion we will focus on those where having insufficient amounts is quickly meaningful to health and performance outcomes with the demands of an athletic lifestyle in mind.

Not All Sources of B6, B9, and B12 Are Equally Effective

Form matters for these B vitamins. Absorption and utilisation differ between forms, and commonly supplemented forms are not the final active compound which works in the body.

1. Pyridoxine requires conversion to pyridoxal-5'-phosphate.
2. Folic acid requires conversion to 5-methyltetrahydrofolate.
3. Cyanocobalamin requires conversion to methylcobalamin.

While this is not the case for every nutrient, for these three supplementing with the final active form is more effective due to the high amount of person-to-person and condition-related variability that precursor forms undergo. By using the final forms we can get more predictable outcomes across the population.

Pyridoxine Inhibiting B6-Dependent Enzymes

Pyridoxine is the most common supplemental form of B6, but can cause toxicity issues at higher doses. Because pyridoxine is inactive and must first be converted to the active form pyridoxal-5'-phosphate (P5P), the unconverted pyridoxine molecule competitively inhibits P5P-dependent enzymes.[6] As the dose increases and is sustained over weeks, this can induce functional B6 deficiency symptoms, causing neuronal toxicity often first noticeable as tingling in the fingers and toes. At low doses this is not a significant issue, but when supplementing with higher quantities more reliably demonstrated to be helpful for sport performance, pyridoxine is not a good choice. P5P is better supplemented with directly for a more reliable result and better safety profile.

Cyanocobalamin Releases Cyanide Requiring Detoxification

Cyanocobalamin is a synthetic B12 compound which is very cheap and common in supplements. While all cobalamin forms ultimately convert to methylcobalamin and adenosylcobalamin intracellularly, cyanocobalamin must first release a cyanide fraction that requires glutathione-dependent detoxification in the liver, creating an undesirable burden particularly in individuals with compromised detoxification capacity or existing cyanide exposure. The doses in typical supplements are not a significant health concern and normal liver function can handle them, but you would be better without it. Due to the multiple conversion steps involved, genetic variation between individuals can cause large differences in effective dosing. Directly supplementing with methylcobalamin simplifies this.

MTHFR Genes and Reduced B9 Conversion

The MTHFR C677T genetic variant affects up to 15% of the population. This polymorphism reduces the enzyme's ability to convert folate (B9) to its active form. Research in soccer players found that those with the TT genotype had significantly lower vitamin B9 levels, also resulting in B12 deficiencies, and higher homocysteine concentrations that can cause toxicity, compared to athletes with CC or CT genotypes.[2]

Elite athletes carrying unfavourable MTHFR genotypes show elevated cardiovascular risk markers including higher advanced oxidation protein products and homocysteine.[3] These individuals may benefit from higher folate intake, ideally as the already active 5-methyltetrahydrofolate form that bypasses the compromised enzyme.

How Exercise Increases Our Need for B6, B9, and B12

The relationship between physical activity and B vitamin status is bidirectional. Exercise stresses metabolic pathways that depend on these vitamins, while deficiency impairs the ability to train and adapt effectively.[1]

Vitamin B6: Amino Acid Conversion and Energy Usage

Amino acid metabolism: Every conversion of one amino acid to another requires PLP. This includes branched-chain amino acid metabolism critical for muscle protein and collagen tissue synthesis.

Glycogen breakdown: During exercise, B6-dependent enzymes release stored muscle glycogen to make more glucose available for fueling energy metabolism.

Neurotransmitter synthesis: B6 is the essential cofactor for aromatic amino acid decarboxylase, the enzyme that converts L-DOPA to dopamine as well as 5-HTP to serotonin.

Vitamin B6, B9, and B12: Oxidative Stress

Homocysteine metabolism: Converting homocysteine to methionine requires B9 to donate a carbon, facilitated by the enzyme methionine synthase, for which B12 serves as a cofactor. B6 is also a critical cofactor for the enzyme cystathionine-beta-synthase, which works in a parallel pathway to convert homocysteine to cystathionine. Without B6, B12, or B9, homocysteine accumulates, causing chronic oxidative stress which increases risk of cognitive decline, heart attacks, stroke, and blood clots.[4] High intensity and prolonged endurance exercise generates reactive oxygen species that compound this burden.

Vitamin B9 and B12: DNA Synthesis and Red Blood Cells

DNA synthesis: Both B9 and B12 are required for DNA synthesis in rapidly dividing cells. Red blood cells turn over every 120 days, and production requires adequate B9 and B12. Deficiency of either is rate-limiting and leads to anaemia, where fewer red blood cells reduce oxygen-carrying capacity. Remaining cells also increase in size to attempt to compensate, which raises clotting risk.

Dietary Restriction

Athletes in weight-class sports, aesthetic sports, and endurance events frequently restrict energy intake. Low Energy Availability (LEA) arises when caloric intake fails to cover both training demands and normal physiological functions.[5] This creates a compounding problem: the athletes working hardest are often the ones eating least, and without strategic management or supplemental intervention, B vitamin insufficiency becomes very likely.

LEA is associated with Relative Energy Deficiency in Sport (RED-S), which encompasses hormonal disruption, decreased bone density, impaired immunity, and compromised performance. Inadequate B vitamin intake is one piece of this picture.

Health Conditions That Increase Nutritional Demand

Beyond baseline athletic requirements, certain populations face elevated B vitamin needs. When an athlete exhibits one or more of these conditions they should be paying close attention.

Will Blood Tests Catch Deficiency?

Serum levels of B12 and folate do not always reflect tissue status. You can have normal blood levels while functional deficiency exists at the cellular level. Homocysteine elevation is often a more sensitive marker, as it rises when B12 or folate function is compromised regardless of serum levels.

The Application of WATTR™

HR Labs WATTR™ includes bioactive forms of all three vitamins: pyridoxal-5'-phosphate (B6), methylcobalamin (B12), and Quatrefolic® 5-methyltetrahydrofolate (B9). These forms bypass conversion steps, making them immediately available for use and improving the safety profile significantly.

WATTR™ is designed to be consumed alongside a normal healthy diet. The B vitamins support the higher demands of energy metabolism during training for those doing five or more sessions a week, complementing the electrolyte profile for hydration. This is particularly relevant for athletes training in conditions that increase both sweat losses and metabolic demand.

For the full breakdown of how each WATTR™ ingredient works, see the WATTR™ article.

Practical Guidelines

For short, moderate sessions: A balanced diet including high-quality meat and vegetables will likely cover B vitamin needs. Focus on meeting requirements across the whole day rather than acute timing.

For high volume training (10+ hours per week): Pay closer attention to B vitamin intake. Consider whether energy restriction or food choices may be creating gaps. Athletes in this category benefit from ensuring adequate intake daily.

For energy restricted periods: This is when supplementation is most clearly beneficial. Cutting calories while maintaining training volume creates peak demand alongside reduced food-based B vitamin intake.

For those with known genetic variants: If you have the MTHFR TT genotype or a family history of elevated homocysteine, prioritise methylated forms of B9 and B12.

Frequently Asked Questions

Can I just take a B complex and cover everything?

Yes, if it is a good one. WATTR™ is a hydration product that also includes a B complex with exclusively the active forms of B6, B9, and B12. Generic B complexes often use inactive forms (cyanocobalamin, folic acid, pyridoxine) at underpowered doses. For some people this might be adequate if their demands are low. For athletes with high turnover and additional factors affecting absorption, conversion, or output, the active forms provide more certainty.

Should I take B vitamins before or after training?

Timing matters less than consistent daily intake. These vitamins support ongoing metabolic processes, not acute performance like caffeine or nitrates. Taking WATTR™ before or during training allows you to benefit from the acute hydration functions of the sodium, taurine, and fructo-oligosaccharides while the B vitamins contribute to your daily total.

Will B vitamins help with muscle cramps?

Probably not directly. Exercise-associated muscle cramps are poorly understood, but the evidence does not support B vitamin deficiency as a primary cause. Electrolyte and hydration status are more relevant factors, which is why WATTR™ addresses both.

How do I know if I am deficient?

Symptoms of marginal deficiency are nonspecific: fatigue, poor recovery, mood changes, frequent illness. Blood tests can help but have limitations (see above). If you fall into higher-risk categories (energy restriction, plant-based diet, high training volume, older athlete, gut issues), ensuring adequate intake is reasonable regardless of test results.

For the science on how sweat losses increase electrolyte demand and how WATTR™ addresses hydration, see the sweat and electrolytes article.

MADE FOR PROGRESS

References

1. Woolf K, Manore MM. B vitamins and exercise: does exercise alter requirements? Int J Sport Nutr Exerc Metab. 2006;16(5):453-484.
2. Dinc N, Yucel SB, Taneli F, Sayin MV. The effect of the MTHFR C677T mutation on athletic performance and the homocysteine level of soccer players and sedentary individuals. J Hum Kinet. 2016;51:61-69.
3. Curro M, Di Mauro D, Bruschetta D, et al. Influence of MTHFR polymorphisms on cardiovascular risk markers in elite athletes. Clin Biochem. 2015;49(1-2):183-185.
4. Mrakic-Sposta S, Gussoni M, Vezzoli A, et al. Acute effects of triathlon race on oxidative stress biomarkers. Oxid Med Cell Longev. 2020;2020:3062807.
5. Cupka M, Sedliak M. Hungry runners: low energy availability in male endurance athletes and its impact on performance and testosterone. Eur J Transl Myol. 2023;33(2):11104.
6. Bisello G, Longo C, Rossignoli G, Phillips RS, Bertoldi M. Oxygen reactivity with pyridoxal 5' phosphate enzymes: biochemical implications and functional relevance. Amino Acids. 2020;52(8):1089-1105.

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This content is for educational purposes only and does not intend to cure or diagnose disease, nor make any health claims. There is no intent to slander in any way, but rather produce an informed and accurate third party perspective on the product. Always consult your accredited medical professional before introducing a new supplement. This content is not to be copied or repurposed in any form without express permission from the author.

First published for HRLABS.co.uk 23rd January 2026