Vitamin C

What is vitamin C?

Vitamin C is water soluble. Its functions include collagen formation, antioxidant activity and improving non-haem iron absorption. Humans need to obtain it through food. [3]

Ascorbic acid and ascorbate occur in different chemical or formulated products. The first dietary question is the actual declared vitamin-C amount. A gram quantity of fruit powder is not a gram quantity of vitamin C.

Read foods and portions carefully

Peppers, citrus fruits, kiwi and broccoli are possible sources. Prolonged storage and heating can reduce their content. [3]

Compare the portion actually consumed. A hypothetical example: 80 mg vitamin C per 100 g provides 120 mg in a 150 g portion. This is an intake calculation, not a general statement about every variety or preparation method.

The same applies to powders: if a 10 g serving declares 60 mg of vitamin C, that is the relevant intake figure. Terms such as fruit complex, extract or botanical origin do not replace a transparent nutrient declaration.

Antioxidant function and clinical benefit

A biochemical function describes what a substance can do in an organism. A clinical trial must also establish whether a particular intervention produces a relevant difference in particular people. These levels should not merge into a general promise of protection.

For vitamin C, the objective is especially important: fewer illnesses, shorter symptoms, higher blood concentrations and improved absorption of another nutrient are four different outcomes. A positive result on one level does not automatically answer the others.

EFSA dietary references

EFSA establishes population reference intakes (PRI) for total intake in healthy people. These are not extra amounts to add to an already adequate diet. [1]

When does supply deserve attention?

Highly restricted diets, certain absorption disorders and smoking can increase the risk of low status. Additional vitamin intake does not remove the health consequences of smoking. [3]

Practical assessment starts with regular meals. A large intake on a single day tells little about how consistently the diet provides the nutrient over time. If there is a limitation, addressing that specific gap is more useful than adopting an ever-higher general target.

Symptoms alone do not reliably identify which nutrient is lacking. People already receiving care for a medical condition should assess additional intake within that treatment context. A vitamin-C reference is neither a diagnosis nor a substitute for investigating persistent symptoms.

Research: five different questions

What does no European UL mean?

EFSA could not derive a tolerable upper intake level because evidence was insufficient. This is not permission for unlimited doses. The safety assessment particularly identifies gastrointestinal intolerance at high intakes. [2]

High intakes require particular assessment with kidney disease, susceptibility to certain kidney stones or iron overload. [3]

A large number on a pack is therefore not proof of quality. Compare its actual nutritional contribution and the evidence for the intended purpose. Several vitamin-containing products need to be considered together.

Which conclusions are useful in everyday life?

For ordinary nutritional adequacy, focus on the whole diet and transparent amounts. For a particular additional application, look for a matching study: the same population, comparable form and amount, and a relevant outcome. “Studied” does not mean “useful for everyone”.

Internal production changes the question

Dogs and cats can synthesise vitamin C from glucose in the liver. The Merck Veterinary Manual therefore describes no general AAFCO dietary requirement. [10]

FEDIAF 2025 provides no separate vitamin-C minimum in its complete-ration tables. [9]

This does not contradict human reference intakes. It demonstrates why a shared ingredient still needs separate perspectives. A human daily amount cannot establish a useful dog dose; equally, a missing table entry does not demonstrate benefit from an arbitrary additional amount.

Nutritional function is not proof of treatment benefit

Ascorbate can also have a technological antioxidant role in food. That role describes the formulation, not evidence that additional amounts prevent disease in an animal. [10]

The human clinical trials presented here cannot answer that veterinary question. A claim about a particular disease would require research in the same species with appropriate outcomes. Human cold studies, for example, cannot support claims about respiratory problems in cats.

Clarify the purpose before the amount

Before adding anything, establish the specific objective, the composition of the complete ration and the evidence supporting that objective in the relevant species. Comparing products solely by milligrams leaves these key questions unanswered.