Fat-Soluble Vitamins A, D, E, and K: Review of the Literature and Points of Interest for the Clinician.

Fat-soluble vitamins, including vitamins A, D, E, and K, are energy-free molecules that are essential to the body's functioning and life. Their intake is almost exclusively exogenous, i.e., dietary. As a result, fat-soluble vitamin deficiencies are rarer in industrialized countries than in countries with limited resources. Certain groups of people are particularly affected, such as newborns or growing children, pregnant or breastfeeding women, and elderly or isolated individuals. Deficiencies in vitamins A, D, E, and K are also relatively frequent in subjects with digestive tract disorders, liver diseases, chronic pathologies, or in intensive care patients. Deficiencies or excesses of fat-soluble vitamins are responsible for a variety of more or less specific clinical pictures. Certain syndromes are typical of fat-soluble vitamin deficiency, such as the combination of ophthalmological and immunity impairments in the case of vitamin A deficiency or hemorrhagic syndrome and osteopenia in the case of vitamin E deficiency. This is also the case for osteomalacia, muscular weakness, even falls, and rickets in the case of vitamin D deficiency. Diagnosis of a deficiency in one of the fat-soluble vitamins relies on blood tests, which are not always essential for routine use. In this context, a therapeutic test may be proposed. Treatment of deficiencies requires vitamin supplementation, a well-balanced diet, and treatment of the cause.