Unique Research Journal of Medicine and Medical Sciences Vol. 4(5), pp. 038-050, September, 2016 Available online@http://www.uniqueresearchjournals.com/URJMMS ISSN 2333-6935 ©2016 Unique Research Journals Unique Research Journal of Medicine and Medical Sciences Full Length Research Paper Determination of 25-OH vitamin D in human serum using the enzyme immunoassay method Olasehinde Oluwaseun Ruth 1 , Owoseni Joseph Sina 2 *, Akawa Oluwole Bidemi 1 and Akintehinse O. V. 1 1 College of Medicine and Health Sciences, Afe Babalola University, Ado Ekiti, Ekiti State, Nigeria. 2 Sociology Department, Ekiti State University, Ado Ekiti, Ekiti State, Nigeria. *Corresponding author. E-mail: owoshynah@yahoo.com. Accepted 22 September, 2016 Vitamin D is a steroid hormone involved in the intestinal absorption of calcium and in the regulation of calcium homeostasis. Serum concentration of 25-hydroxyl Vitamin D is considered to be the most reliable measure of overall vitamin D status. This research work focused on the quantitative determination of the 25-OH Vitamin D in the serum of young people aged 20 to 30 years and adults aged 45 to 65 years, using Enzyme-Immuno-Assay (EIA) (a competitive protein binding assay). The results showed that 23.5%young people were deficient in 25(OH)D (<30 nmol/L) and 76.5% exhibited 25(OH)D insufficiency (30-75 nmol/L). In the adult group, 33.3% were deficient (30 nmol/L), 50% were normal (30- 75 nmol/L) and 16.6% were sufficient in vitamin D levels. This study revealed that vitamin D deficiency was found in both youths and adults but higher in the adults. The study showed that vitamin D levels are reduced in adults compared with young people. Key words: 25-OH Vitamin D, enzyme immunoassay method, adult, young people. INTRODUCTION A vitamin is an organic compound required as a nutrient in tiny amounts by an organism (Lieberman and Bruning, 1990). In other words, an organic chemical compound or related set of compounds is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and on the particular organism. For example, ascorbic acid (Vitamin C) is a vitamin for humans, but not for most other animals, and biotin and vitamin D are required in the human (Janet Raloff, 2006). By convention, the term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids (which are needed in larger amounts than vitamins), nor does it encompass the large number of other nutrients that promote health but are otherwise required less often (Grimes, 1996). Thirteen vitamins are presently universally recognized. Vitamins are classified by their biological and chemical activity, not their structure. Thus, each "vitamin" refers to a number of vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals is grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A", which includes the compounds retinal, retinol, and four known carotenoids. Vitamers by definition are convertible to the active form of the vitamin in the body, and are sometimes inter- convertible to one another, as well (Chen, 2005). CLASSIFICATION OF VITAMINS Vitamins are classified into two categories: