Snapshot series 7: Fat soluble Vitamins

Vitamins A, D, E and K comprise a small group of fat-soluble vitamins of disparate chemical composition which are essential for good health. 

Various processes are dependent on an adequate availability of these vitamins, including vision (vitamin A), growth and tissue differentiation (vitamins A and D), bone and muscle function (vitamin D), immune function (vitamin A), protection against  free radicals (vitamin E) and blood clotting (vitamin  K). Although fat-soluble vitamins can  be stored in the body for use in times of dietary scarcity, deficiencies do occur, with profound consequences. 

In some regions of the world, young children are at risk of becoming blind because of inadequate vitamin A. Vitamin D deficiency, which is common worldwide, may cause bowed legs and pelvic deformities of rickets in children and muscle weakness and bone pain of osteomalacia in adults. 

Foods  of animal origin tend to be good sources of fat-soluble vitamins, but red, yellow and  orange vegetables are an excellent source of carotenoids  (a form of vitamin A), and vitamins  E and K are found in nuts and seeds. Vitamin D is unusual as humans can synthesize it through sunlight on skin, which is important because only a few foods are rich in vitamin D.

High-dose supplements of some fat-soluble vitamins can have severe adverse effects. High-dose supplements of vitamin D can actually increase fracture risk and may cause damage to the heart and kidneys. 

Vitamin A is toxic at high doses, causing serious birth defects and possibly fractures. In smokers, too much beta-carotene (a form of vitamin A) may even increase the risk of death from lung cancer.