A set of vitamers with related biological activity are grouped together by a general name, or generic descriptor, that refers to similar compounds with the same vitamin function.
These differences include abundance in the typical diet, bioavailability, toxicity, physiological activities, and metabolism.
For example, hypervitaminosis A is a toxicity syndrome caused by excess consumption of retinoid vitamers of vitamin A such as retinol, retinal, and retinoic acid.
[3] As part of an overall diet, minimally processed foods provide a number of different naturally occurring vitamers.
This is frequently in contrast to fortified foods and dietary supplements which generally provide vitamins as a single vitamer.
Many plant-based foods provide all eight naturally occurring vitamers of vitamin E in varying amounts from different sources.
The liver recognizes and preferentially re-secretes α-tocopherol into circulation, making it the most abundant vitamer of vitamin E in the blood.
Sometimes referred to as "food folates", these vitamers are characterized as pteroylpolyglutamates and contain between one and six additional glutamate molecules compared to folic acid.
After digestion, food folates are converted in the small intestine to 5-methyltetrahydrofolic acid, a biologically active vitamer of vitamin B9.
Folic acid is absorbed and transported in the bloodstream to the liver, where it is converted to tetrahydrofolate, a second biologically active vitamer, by dihydrofolate reductase.