Why do most vitamins need to come from food?

While humans can synthesize certain vitamins to a limited extent—such as vitamin D through sunlight exposure, niacin from the amino acid tryptophan, and vitamin K and biotin via gut bacteria—the body generally cannot produce these essential organic compounds in sufficient quantities to meet its metabolic needs.12

Because the body cannot manufacture most vitamins internally, we depend on our diet to supply them. These compounds are vital for facilitating metabolic and physiological processes, such as energy metabolism, immune function, and tissue development. When dietary intake is inadequate, the body cannot properly regulate these essential reactions, leading to deficiency syndromes. Relying on a balanced diet is the most reliable way to ensure the body receives the necessary amounts of these nutrients, as vitamins found in food come associated with other beneficial substances and carry a lower risk of toxicity compared to high-dose supplements.134