In 1912, the Polish scientist and biochemist Kazimierz Funk coined the term “vitamins” – yet we often overlook that researchers like the nutrition researcher Elmer McCollum, along with colleagues in the 1910s and 1920s, played a crucial role in identifying fat-soluble vitamins, while dietitians in community clinics helped millions of families through education to prevent deficiencies. This historical turning point changed medicine: small molecules, big impact. Today, high performers face a new challenge: debunking myths, utilizing evidence – for energy, focus, and longevity.

Vitamins are essential micronutrients that the body cannot produce in sufficient quantities. They are classified into fat-soluble vitamins fat-solubleabsorbed in fats and stored in tissues; examples include A, D, E, K and water-soluble vitamins water-solublenot stored, excesses are excreted through the kidneys; primarily B vitamins and vitamin C. The storage characteristic of fat-soluble vitamins means: deficiencies and excesses are both possible. Vitamin D is also a prohormoneprecursor of a hormone with regulatory effects on calcium/phosphate and other systems. What matters in practice is: meet the needs, avoid overdoses, and consider individual risks.

Balance decides performance. Studies show that deficiencies in fat-soluble vitamins can weaken the immune system, bones, and blood coagulation – whereas overdoses can be toxic, especially since these vitamins are stored in liver and fat tissues ^[1]. Vitamin D is central to bone health and selected extraskeletal processes; targeted supplementation is particularly beneficial for at-risk groups and in combination with calcium to prevent deficiency-related disorders ^[2]. However, excessive intake is no shortcut: for vitamin E, for example, reviews suggest risks associated with high-dose use, including an increased tendency to bleed – especially when taken simultaneously with anticoagulants ^[3]. And those who categorize “natural” products as automatically safe overlook the evidence: herbal supplements are often subject to lax quality and labeling standards; interactions and liver damage have been documented ^{[4] [5] [6]}. In short: smart dosing instead of “more is more.”

Regarding toxicity, recent reviews indicate that fat-soluble vitamins, especially A, can cause both acute and chronic side effects – ranging from neurological symptoms to liver and bone involvement. The cause is often excessive, non-indicated supplementation, facilitated by easy availability; guideline-conforming approaches call for thorough history-taking, laboratory testing, and consistent discontinuation at the suspicion of toxicity ^[1]. Complementarily, a systematic review on vitamin A hypervitaminosis states that cases often result from OTC preparations; clinically, hypercalcemia and neurogastrointestinal complaints dominate, and management includes cessation and supportive therapies ^[7]. On the benefits side, a metabolomic RCT on multivitamins in healthy individuals shows effects on homocysteine and markers of energy metabolism; this demonstrates physiological activity but does not replace personalized needs assessment ^[8]. Narrative reviews summarize that MVM can be valuable for at-risk groups but require standardized formulations, safety testing, and adherence to RDA and upper intake levels to avoid excessive intake ^[9]. For vitamin D, the message is clear: target testing and supplementation – significant benefits in cases of deficiency and defined clinical situations, minimal additional benefits without a deficiency ^[2].

- Have your 25-OH vitamin D level checked in late fall/winter and supplement if a deficiency is diagnosed, based on medical advice; combine with calcium if medically indicated ^[2].
- Avoid high doses of fat-soluble vitamins (A, D, E, K) without clear indication. Observe upper intake levels and prefer a diet as the foundation ^[1].
- When choosing a multivitamin, opt for certified products that do not exceed RDAs, and check for evidence and quality seals (e.g., independent lab tests) ^{[8] [9]}.
- Seek medical advice before starting new supplements, especially if you have pre-existing conditions or are taking medications like anticoagulants; high doses of vitamin E can promote bleeding ^[3].
- Correct the fallacy “natural = safe”: check for interactions and liver risks of herbal products, particularly those for weight loss ^{[4] [5] [6]}.

Performance loves precision: properly dosed vitamins support health and longevity, while excess can be harmful. Assess, personalize, then act – transforming supplementation from myth to measurable advantage.