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The Importance of Vitamin Intake for Human Nutrition, Fitness, and Health

By Friedrich Reuss, Egloffstein

Vitamins are organic substances that have a catalytic function in the body in the biochemical reactions of metabolism. They must be supplied from outside and are not building materials of the body (otherwise, for example, amino acids would also have to be counted among the vitamins).
\nThe classic view assumes that an insufficient supply of a vitamin quickly leads to a reduction in the relevant biochemical reactions and ultimately to the collapse of the body.

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A severe vitamin deficiency is not compatible with life in the long term.

Based on this concept, vitamin researchers long believed they could determine human vitamin requirements quickly and reliably through experiments that create an artificial vitamin deficiency. Initial uncertainties in the method arose from the fact that tolerance of a borderline vitamin supply was found to vary greatly among people. This is evidently dependent on genetic factors (including absorption), on the presence and availability of other nutrients, and on current metabolic activity.

Later it was recognized that most vitamins control a large number of biochemical reactions and that different amounts of vitamins are sufficient for their function. Thus, the experimentally determined human vitamin requirement depends on the metabolic function used as the benchmark.

In this situation, it is clear that the human vitamin requirement ultimately depends on the biochemical function that requires the highest intake of a vitamin. That sounds simple, but it has far-reaching consequences, because no one can assume that we already know all the functions of a vitamin. The opposite is probably more likely to be true, namely that for most vitamins we do not yet know all the functions they control.

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A typical example is vitamin K, which used to be regarded only as a coagulation vitamin and for which a vitamin requirement of about 40–80 µg per day was then assumed. Today we know that vitamin K also plays a very important role in the synthesis and remodeling of collagen and bone substance. For this function, however, much higher vitamin intakes are obviously optimal—the discussion currently ranges between 250 and 1,000 µg (amounts that can certainly be achieved with green vegetables).

A similar example is vitamin C, for which very small amounts (20–40 mg) are apparently sufficient to maintain collagen synthesis in humans. For antioxidant cell protection, however, much higher intakes (roughly between 200 and 1,000 mg) are required, and here we are still in the phase of dose optimization.

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Effects of a Vitamin Deficiency

Some vitamin effects take place, as it were, in secret, and the difference between a good and a poor vitamin supply only becomes visible after months, years, or even decades. These are periods that go far beyond the time frame of earlier vitamin studies. Precise new scientific findings can only be expected here after a long time. Especially with vitamins that have an antioxidant effect, studies to identify an optimal supply are difficult because damage caused by insufficient vitamin supply often only becomes visible after decades.

Although the biochemist or laboratory physician can estimate antioxidant cell protection using some laboratory values, the influence on long-term health can only be reliably assessed and quantified under real-time conditions.

The situation is similar with vitamin effects that are intended to ensure cancer protection or the maintenance of an efficient immune system in healthy individuals.

In this situation, the highly ethical health-policy question arises as to whether one should wait until, for example, cancer protection through antioxidant nutrients has been measured exactly, or whether vitamin recommendations should be raised as soon as the positive trend has been confirmed, without any harmful effect being known. We currently face this core question particularly with antioxidant vitamins.

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We know that a substantially higher intake than the basic intake recommended to date reduces the risk of numerous diseases. Nevertheless, the authorities in some countries refuse to recognize higher vitamin intakes as nutrition. Apparently, many millions more people must die of lifestyle diseases before statistical data are good enough for the authorities and national nutrition societies to significantly raise vitamin consumption recommendations.

Of course, vitamin dosages should be set so that no harm can come to people even under unfavorable circumstances. Decades of experience with the use of dietary supplements in countries with “liberal food law” have shown that serious undesirable vitamin effects are extremely rare. To the extent that intoxications became known at all, they were based on gross misuse or on serious misdosing of critical vitamins by the manufacturer. Thus, it was soon realized that only vitamins A and D actually pose a certain risk, because here the safety factor between recommended intake and a possibly adverse dose is less than 10. More recent scientific findings, however, have largely given the all-clear here as well: vitamin A is no longer considered nearly as embryotoxic today, and vitamin D, according to current knowledge, is also harmless up to relatively high and generally unnecessarily high dosages. The strict limitation of dietary supplementation with vitamins A and D in Germany is therefore scientifically long outdated; nevertheless, there has been no change in thinking by the German authorities. Only the constraints imposed by EU law will initiate normalization here.

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Official Recommendations – Optimal Supply?

In simplified terms, it can be said today that the B vitamins, vitamin C, and vitamin E are safe up to 100 times the official basic recommendation, and vitamins A and K up to 10 times, and vitamin D at least up to 5 times.
\nWe can therefore use modern vitamin dosages without relevant risks. However, it is always wise to use vitamins in sensible combinations and not to consume a single vitamin in extreme doses. In this context, it is important to know that even the beneficial antioxidant vitamins can become pro-oxidative when supplied excessively—if they are taken individually. Combining the antioxidant vitamins with one another and with antioxidant secondary plant compounds eliminates the pro-oxidative risk with a high degree of certainty, so that food-law quantity limits for the nutrients mentioned are not justified.

A new way of approaching optimal vitamin intake is Stone Age nutrition research. Various research groups around the world have compiled findings on the diet of our ancestors. Despite all the differences due to climatic and regional variations, it can be said that our ancestors consumed up to 10 times as many vitamins (and other micronutrients) as the current official recommendations state. Further details on this can be found" }, "media": { "images": [ { "url": "https://drreinwald.com/wp-content/uploads/2025/11/header-artikel-vitaminzufuhr.jpg", "alt": "", "type": "featured", "id": 1303 } ], "featured_image": { "url": "https://drreinwald.com/wp-content/uploads/2025/11/header-artikel-vitaminzufuhr.jpg", "alt": "" } }, "ai_context": { "faq": { "type": "summary", "source": "generated", "visible": false, "confidence": "high", "purpose": [ "semantic_comprehension", "entity_disambiguation", "answer_generation" ] }, "semantic_qa": { "type": "summary", "source": "generated", "visible": false, "confidence": "low", "quality_score": 0, "purpose": [ "semantic_comprehension", "entity_disambiguation", "answer_generation" ], "items": [ { "answer": "Vitamins support essential biochemical reactions in metabolism. They help regulate processes linked to energy production, tissue maintenance, immunity, antioxidant protection and long-term health.", "question": "Why are vitamins important for human nutrition?" }, { "answer": "Most vitamins must be supplied through food or supplements because the body cannot produce them in sufficient amounts. This makes regular dietary intake essential.", "question": "Can the body produce vitamins on its own?" }, { "answer": "A low vitamin intake can reduce important metabolic functions and may eventually contribute to deficiency symptoms, weakened immunity, poor tissue repair or long-term health risks.", "question": "What happens when vitamin intake is too low?" }, { "answer": "Official recommendations often aim to prevent deficiency, but the article argues that optimal intake for antioxidant protection, bone health or immune function may be higher for some vitamins.", "question": "Are official vitamin recommendations always optimal?" }, { "answer": "Vitamin requirements can vary due to genetics, absorption capacity, availability of other nutrients, metabolic activity, lifestyle, age, diet quality and overall health status.", "question": "Why may vitamin needs differ from person to person?" }, { "answer": "Vitamins A and D have historically required more caution because the safety margin between recommended intake and excessive intake is smaller than for many water-soluble vitamins.", "question": "Which vitamins require special caution at high doses?" }, { "answer": "Modern agriculture, milling, storage and industrial processing can reduce vitamin density in foods, making it harder for some diets to provide optimal micronutrient levels.", "question": "How has modern food processing affected vitamin intake?" } ] } }, "faq_detection": { "status": "none", "visible": false, "source": "", "source_label": "", "quality_score": 0, "item_count": 0 }, "related": [ { "title": "Natural Remedies – There Is an Herb for Every Illness", "url": "https://drreinwald.com/en/natural-remedies-there-is-an-herb-for-every-illness/", "type": "post" }, { "title": "Camu Camu – the little vitamin C bomb from South America", "url": "https://drreinwald.com/en/camu-camu-the-little-vitamin-c-bomb-from-south-america/", "type": "post" }, { "title": "Silent Inflammation: The Underestimated Danger in Our Body", "url": "https://drreinwald.com/en/silent-inflammation-the-underestimated-danger-in-our-body/", "type": "post" }, { "title": "Enzymes – Sparks for Health and Well-Being", "url": "https://drreinwald.com/en/enzymes-sparks-for-health-and-well-being/", "type": "post" }, { "title": "Glutathione: a Little Miracle", "url": "https://drreinwald.com/en/glutathione-a-little-miracle/", "type": "post" } ] }