Safety of vitamin A

Abstract

Vitamin A adequacy is discussed in terms of the recommended allowances appropriate for the needs of the majority of individuals. Deficiency can result in xerophthalmia and permanent blindness and in increased mortality rates among children. Toxicity has been associated with the overconsumption of vitamin A supplements. Acute hypervitaminosis A may occur after ingestion of greater than or equal to 500,000 IU (over 100 times the RDA) by adults or proportionately less by children. Symptoms are usually reversible on cessation of overdosing. Factors influencing chronic hypervitaminosis A include dosing regimen, physical form of the vitamin, general health status, dietary factors such as ethanol and protein intake, and interactions with vitamins C, D, E, and K. Both excess and deficiency of vitamin A in pregnant animals was shown to be teratogenic. In humans, congenital malformations associated with maternal over-use of high doses of vitamin A were reported but no cause-and-effect relationship has been established. Deficiency of the vitamin during pregnancy has also been associated with congenital abnormalities. Reported incidences of vitamin A toxicity are rare and have averaged fewer than 10 cases per year from 1976 to 1987.

Vitamins, Are They Safe?

“…Vitamin A is an essential agent for vision, embryogenesis, reproduction, the integrity of membrane structures, epithelial differentiation, growth, and development. 51,52 Epidemiologic studies have shown a reduced risk of various chronic diseases, particularly cancers of lung, gastrointestinal tract, bladder, breast and pancreas and cardiovascular disease with dietary consumption of various carotenoids. [53][54][55][56][57][58][59][60][61] However, randomized clinical trials have not shown any consistent reduction in the incidence of cancers or cancer deaths, or of cardiovascular disease.…”

“…Retinoic acid inhibits osteoblast activity, stimulates osteoclast formation, and induces bone resorption. 51,67 Folic acid Folate is a member of vitamin B family and a watersoluble vitamin. It is used for nucleotide biosynthesis, DNA replication, and methylation reactions in body.…”

The neurobiology of retinoic acid in affective disorders

“…1), and several alternative pathways also exist into which vitamin A may be channeled, vitamin A would not be expected to be as potent as RA. Indeed, large doses of vitamin A can have a number of other neurological and mental effects including nausea, vomiting, weakness, fatigue, irritability, drowsiness, loss of appetite, ataxia, decreased interest, headache, and diplopia (double vision) (Bass 1959;Bendich and Langseth 1989;Fishbane et al 1995;Gerber et al 1954;Restak 1972;Rodahl and Moore 1943;Shaw and Niccoli 1953;Stimson 1961). These effects appear to be more common in children and adolescents (Lombaert and Carton 1976;Pasquariello et al 1977;Stimson 1961).…”

The EUROSCAN Study

“…Vitamin A has proven to be a relatively safe and non-toxic drug, even when given in high doses and for a long period (Silverman et al, 1963;Bendich et al, 1989). Retinol Palmitate in an emulsified form has optimal features with regard to intestinal absorbtion, availability from the tissue, with limited liver toxicity.…”