Vitamin requirement study techniques

Vitamin requirement studies have been conducted for 50 years using growth and clinical signs of deficiency for quantitative studies. Histological confirmation of apparent signs confirm and establish subclinical measurements for deficiency. Test diets for these studies with positive experimental control over the test vitamin have been developed using varying degrees of vitamin‐free ingredients in the formulations. Haematology values and microanatomical changes reflect failures of a metabolic system and provide convincing data for requirements. Quantitative studies have used specific test diets plus increasing aliquots of the test vitamin, coupled with growth response, tissue storage analysis, and specific enzyme system activity. Results have been reported for levels which support normal growth, clinical enzyme saturation, and maximum liver or other tissue storage levels. Megavitamin intake studies have been correlated with improved resistance to stress and certain fish diseases. Statistical measurement of response to various parameters used become essential for quantitative vitamin requirement determinations. Early studies using vitamin analysis of feedstuffs mixtures coupled with growth response, absence of deficiency signs, and liver or tissue storage have been superseded by diets with more positive control of all nutrients, including the vitamin to be tested. Sparing effects of one vitamin upon another can be demonstrated. Various vitamer forms may have different activity to supply physiological requirements for the vitamin. Most water‐soluble vitamins act as co‐enzymes in metabolic systems. Some fat‐soluble vitamins have molecular functions acting as hormones, free radical traps, intracellular reducing agents, pigments, antioxidants, etc. A guide for vitamin requirements or dietary allowances should be followed when research plans are made to conduct vitamin requirement studies.