Facts & Myths

Administration of the active form of vitamin B6, pyridoxal 5 phosphate or PLP, cannot generally be regarded as clearly more advantageous than supplementation with pyridoxine hydrochloride.

Phosphorylated forms of vitamin B6 are dephosphorylated before absorption in the intestine and are metabolically activated again in the body after absorption. [3] The term “active form” therefore does not automatically mean a better biological or clinical effect. [27]

The combination of magnesium and vitamin B6 has a certain biological rationale. Magnesium participates in vitamin B6 metabolism as a cofactor for enzymes involved in its conversion. [28]

Available clinical data suggest a possible greater effect in some selected groups, such as people experiencing high levels of stress who also have low magnesium levels. However, the combination cannot generally be considered more effective than supplementation with magnesium alone. [18] [19]

Water solubility may reduce the risk of accumulation for some vitamins, but it does not mean there is no risk of adverse effects or interactions with other substances. Individual B vitamins differ considerably in terms of safety. [29]

This is most evident with vitamin B6, where long term intake of high doses may lead to peripheral neuropathy. [3]

The idea that B complex boosts energy metabolism is based on a simplification of the physiological roles of B vitamins.

Vitamin B5 plays the most prominent role in this respect because, as a precursor of coenzyme A, it directly enters pathways that enable nutrients to be used for energy production. [2]

Vitamin B6 participates in energy metabolism primarily through amino acid and glycogen metabolism. [3] Folic acid and vitamin B12 have a more indirect role through homocysteine, methionine and related pathways. [4] [5]

Energy itself is provided by the main macronutrients, namely carbohydrates, fats and proteins. [30]

Without a proven deficiency or increased need, high doses of B vitamins are not automatically more beneficial.

This principle is particularly apparent with vitamin B12 because its absorption depends on the limited capacity of intrinsic factor. As the oral dose increases, the proportion that is actually absorbed decreases. Higher doses may therefore be appropriate in cases of deficiency or impaired absorption, but in a person without an increased need they do not automatically produce a greater effect. [5]

For vitamin B6, the aim is not to take the highest possible dose, but to meet the body’s needs. Long term intake of high doses may increase the risk of peripheral neuropathy. [3] [22]

During creatine supplementation, creatinine levels in the blood or urine may increase slightly because part of creatine is naturally converted into creatinine in the body. An increase in creatinine alone therefore does not automatically indicate kidney damage.

Meta-analyses show that, in healthy individuals taking standard doses of approximately 3–5 g per day, there is no significant deterioration in kidney function, such as a reduction in glomerular filtration rate (GFR). Creatine monohydrate is generally considered safe when the recommended dosage is followed. However, caution is appropriate in people with pre-existing kidney disease. [16]

Creatine may have a place in the supplementation regimen of endurance athletes, but typically not as an enhancer of purely aerobic endurance.

For endurance athletes, supplementation makes the most sense in situations where performance depends on repeated short, high-intensity efforts, such as intervals, surges or a finishing sprint. It may also be beneficial during strength preparation. Its relevance therefore lies primarily in supporting high-intensity training rather than improving pure endurance performance. [17]

Human studies investigating the effects of creatine supplementation on memory and concentration have produced mixed results. Some studies report improvements in cognitive function, while others show no effect.

Improvements in memory have been observed particularly in healthy older adults aged 68–85 and in the working memory of vegetarians and vegans. In a direct comparison between vegetarians and omnivores, memory improvement following creatine supplementation was more pronounced among vegetarians. However, other studies have not demonstrated a benefit for memory in children, adults or some groups of older people.

For concentration and attention, the effect of creatine supplementation appears most likely during sleep deprivation. Creatine may improve cognitive performance, including memory and attention, but the effects appear more consistently when the brain is under strain—for example, because of insufficient sleep or a neurodegenerative disorder such as Parkinson’s or Alzheimer’s disease. [18]

Creatine is not relevant exclusively to athletes. It plays a role in short-term, high-intensity physical exertion, including ordinary activities such as running to catch a bus or lifting a heavy object.

The body naturally produces creatine, while supplementation increases its creatine stores. This may help the body perform short, intense tasks and manage repeated high-intensity efforts. Review studies indicate that the potential applications of creatine are not limited to athletes or structured exercise. [1]

Vitamin C helps increase the bioavailability of non haem iron. [1] However, available clinical data do not show that routinely adding vitamin C to oral iron leads to a significantly greater increase in haemoglobin or ferritin compared with taking iron alone. [16]

It is therefore more accurate to say that vitamin C may be a useful addition, but it is not essential for iron absorption.

In some studies, ferrous bisglycinate has been associated with a lower incidence of adverse effects, particularly gastrointestinal adverse effects, compared with ferrous sulphate. [17]

However, current data do not show that it generally produces a greater increase in ferritin, haemoglobin or iron stores than ferrous sulphate. [18] Ferrous sulphate is also available in the Czech Republic as a registered medicinal product. [13]

Vegetarians and vegans may have lower iron stores more frequently than people who consume animal products. However, this does not mean that every vegetarian or vegan automatically has anaemia or a clinical iron deficiency.

Studies show that vegetarians more frequently have lower iron stores, particularly when measured using ferritin. However, this is not an automatic rule for every individual.

Regular monitoring of blood parameters is therefore recommended for these population groups. This may include iron, haemoglobin, ferritin and, where appropriate, transferrin. [19]

With iron, a higher dose does not automatically produce a better effect. Higher or unnecessarily frequent doses increase the risk of adverse effects, particularly those involving the digestive tract. If used inappropriately, excessive iron intake may also lead to toxicity.

It therefore makes sense to follow the recommended dosage and adjust supplementation according to an actual deficiency. [1]

According to the authorised health claim for magnesium that may be used for food supplements, magnesium contributes to the reduction of tiredness and fatigue. [19] However, fatigue can have many other causes and is not always associated with magnesium deficiency. One of the main factors is sleep, typically 7 to 9 hours per night, and good sleep hygiene, including limiting exposure to light from screens, particularly mobile phones and televisions, before bedtime. Diet and potential deficiencies in other nutrients involved in energy-yielding metabolism, such as iron, may also play an important role. Therefore, if you feel tired, before reaching for a food supplement, make sure that you are getting enough sleep and eating a varied diet. If the fatigue persists, worsens or is accompanied by other symptoms, it is advisable to discuss the underlying cause with a doctor.

Magnesium oxide itself is less soluble and may therefore also be less readily utilised by the body. However, in some supplements it is combined with citric acid, often in effervescent tablets, and once dissolved, magnesium citrate may form in the solution. This generally behaves more favourably in terms of solubility. [13] It is therefore always important to read the list of ingredients on the label.

Magnesium carbonate reacts with hydrochloric acid in the stomach to form magnesium chloride. [14] However, it does not make sense to assign a single fixed absorption percentage to a particular magnesium salt, as absorption varies considerably depending on the dose and the individual. Ultimately, magnesium is absorbed into the bloodstream as the Mg²⁺ ion. [3] The quantities of the so called carriers found in magnesium tablets, such as bisglycinate or malate, are not sufficient to produce the therapeutic effects sometimes described by manufacturers. For example, one study administered 3 g of glycine per day and observed a modest improvement in sleep. [15] Such an amount is unlikely to be found in magnesium tablets. Attempting to reach this level may also increase the risk of gastrointestinal problems, particularly diarrhoea. [1]

At higher doses, magnesium citrate can have a laxative effect, particularly when taken on an empty stomach. [16] In practice, this can often be avoided by dividing the daily dose into smaller portions, for example, two or three doses per day, and taking them with or after food. Magnesium is generally better tolerated in this way, and its overall utilisation may also improve because the body is not presented with one large dose at once. [17]

Malate, the anion of malic acid, is a naturally occurring intermediate in the citric acid cycle, also known as the Krebs cycle. In supplements such as magnesium malate, malate primarily serves as a carrier for magnesium. Once ingested, it behaves like an ordinary organic acid that the body is able to metabolise. However, in a healthy person, the amount of malate supplied by a capsule is not generally a limiting factor in the speed of the Krebs cycle. The cycle is primarily controlled by the cell’s energy status, including the ATP to ADP and NADH to NAD⁺ ratios, the availability of oxaloacetate, which is an intermediate in the Krebs cycle, and the regulation of key enzymes. The Krebs cycle itself produces only a small amount of energy directly, one molecule of GTP, which is energetically equivalent to ATP. Its principal role is to generate NADH and FADH₂, which subsequently drive oxidative phosphorylation, where most cellular ATP is produced. [18]

Ubiquinone is essential for electron transfer in the mitochondrial respiratory chain and therefore for ATP production. Direct antioxidant activity is shown mainly by the reduced form, ubiquinol, which can neutralise free radicals. However, in the body, both forms are continuously converted into one another and function as a redox pair. It is therefore not correct to set them against each other: both ubiquinone and ubiquinol have an indispensable role in the body, both in energy metabolism and in antioxidant protection. [9]

Differences in bioavailability between ubiquinol and ubiquinone are not consistent across studies and cannot be generalised. In practice, the decisive factors are often primarily the formulation (solubility/dispersion in an oil carrier), use with a meal containing fat, and individual factors (bile acids, fat digestion, transport in lipoproteins). In addition, both forms are continuously interconverted in the body, so the “better form” without specifying the particular product and administration conditions is misleading. [10]

Coenzyme Q10 is not a “fuel” that produces extra energy by itself. It can be imagined as part of the cellular “engine” that helps energy production proceed properly. However, it does not follow from this that the higher the intake of coenzyme Q10, the more energy will automatically be produced in the form of ATP. In most healthy persons, the amount of coenzyme Q10 is not what limits ATP production. [2]

The main source for ATP production is nutrients from food, especially carbohydrates and fats (fatty acids). These provide the body with energy and the “material” from which ATP is produced. In this process, coenzyme Q10 serves as an assistant in electron transfer in mitochondria, not as an energy source. In some groups—for example, at older age or in selected health conditions, coenzyme Q10 supplementation may have a rational basis; however, it cannot be understood as a universal means of “increasing energy” for everyone. [11]

Food supplements are classified in legislation as foods and, unlike medicinal products, they do not undergo a registration procedure before being placed on the market that would assess their quality, safety and efficacy in advance. In practice, supervision of food supplements therefore relies mainly on ongoing inspections (safety, labelling and prevention of consumer deception).

Inspections also show that, in food supplements, cases may occur in which a product does not contain the declared substances, or their amount is lower than stated on the label. For this reason, it makes more sense to evaluate a product according to its formulation and dose and, ideally, according to independent quality verification, rather than according to price.

If the manufacturer publishes current reports from an independent laboratory (qualitative and quantitative analysis, and possibly contaminants), this represents an above-standard level of transparency that significantly increases the product’s credibility. [12]

This is one of the most common myths surrounding vitamin C. The body strictly regulates the intake and distribution of ascorbic acid. Cells take up vitamin C through specific transporters that have limited capacity, and the body also keeps the plasma concentration of vitamin C under relatively tight control.

At high doses, there is therefore typically a marked increase in the blood level, but the excess is then rapidly excreted by the kidneys. Long term administration of high doses, in the range of grams to tens of grams per day, may represent an unnecessary renal burden and a higher risk of adverse effects.

Intravenous administration of lower doses, such as 500 mg, may make sense primarily when oral use is not possible or suitable, for example because of intolerance, vomiting or malabsorption. In an otherwise healthy person, however, the infusion itself usually does not provide an additional effect compared with rational oral intake. [8]

Vitamin C is chemically ascorbic acid. In food supplements, it may occur either directly as ascorbic acid or in the form of its salts, such as sodium or calcium ascorbate.

These forms are still chemical derivatives of ascorbic acid, and the body uses them in the same way. Ascorbates are also commonly used in the food industry, primarily for the antioxidant effect of vitamin C. [14]

However, this is not an automatic rule for every individual. Nevertheless, regular monitoring of the blood count, especially iron, haemoglobin, ferritin and, where appropriate, transferrin, is recommended in these population groups.

In practice, liposomal vitamin C is vitamin C enclosed in a fat based coating. As a result, a slightly greater amount may enter the blood in some people compared with the conventional form. However, this does not automatically mean a greater effect.

The body has its own limits for vitamin C. Cells can take it up only to a certain extent. What they no longer need or cannot absorb is not utilised, and the excess is then rapidly excreted by the kidneys. In a healthy person, this therefore often means primarily a higher short term blood level, not a miraculously stronger effect. [15]

In humans, it has not been reliably demonstrated that rosehip flavonoids improve the absorption or increase the effect of vitamin C compared with ascorbic acid alone.

In food supplements, rosehip is therefore usually only an additional plant ingredient. The main active substance remains vitamin C. If the aim is to supplement vitamin C, what primarily matters is its dose and the body’s need, not whether the product contains rosehip. [16]

Vitamin D is a fat soluble vitamin and is absorbed in the intestine together with fats. This does not mean, however, that it is not absorbed at all without a meal containing fat. Absorption still occurs, but is usually lower. The presence of fat in a meal typically increases the bioavailability of vitamin D. [9]

Vitamin D2, also known as ergocalciferol, and vitamin D3, also known as cholecalciferol, are both precursors of the active hormonal form. They are gradually converted in the body into 25(OH) vitamin D and subsequently into calcitriol, the active form of vitamin D.

Vitamin D2 is formed from ergosterol, mainly in mushrooms and yeasts following exposure to ultraviolet radiation. It is also found in fortified foods. Vitamin D3 is formed in the skin from 7 dehydrocholesterol under the influence of ultraviolet radiation and is also found in animal sources such as fatty fish.

Vitamin D2 is converted in the body into the active form, just like vitamin D3. It is particularly suitable for people seeking a source that is not derived from animals. [4]

This statement is not correct because the primary aim is to achieve an adequate vitamin D status, not to maximise the dose. The clinical benefit of supplementation is most pronounced in cases of deficiency. Excessive intake also increases the risk of adverse effects.

The main concern associated with vitamin D toxicity is hypercalcaemia caused by increased intestinal absorption of calcium. In the general population, toxicity is rare when standard doses are used, but it can occur with the long term use of high doses. [7]

In the immune system, vitamin D acts mainly as a regulator, also described as an immunomodulator. Immune cells can respond to vitamin D because they have vitamin D receptors. Some immune cells can also produce the active form locally, allowing vitamin D to influence the course of an immune response directly in the tissue.

In practice, vitamin D supports the basic defence mechanisms of innate immunity and helps ensure that the inflammatory response is not disproportionate. [7]

For this reason, the following health claim is permitted in the European Union: “Vitamin D contributes to the normal function of the immune system.” [10]

The statement that vitamin D does not work without vitamin K is a simplification and is not correct in this form. The active form of vitamin D demonstrably increases the intestinal absorption of calcium. It does not require a vitamin K2 supplement as a condition for its effect.

Vitamin K1 and vitamin K2 have a different role. Vitamin K is a cofactor required for the activation of certain proteins involved in handling calcium in bone tissue and soft tissues. From a mechanistic perspective, it therefore makes sense that vitamins D and K may act synergistically. However, this does not mean that vitamin D is ineffective without vitamin K.

Clinically significant vitamin K deficiency is also rare in adults. For most people with a normal diet, vitamin K2 is therefore not a necessary condition for vitamin D to work, but it may represent a potential additional benefit in individual situations. [7]