The recommended daily amount of vitamin A for adult men is 900 micrograms (mcg) and 700 mcg for adult women. You can get all the vitamin A you need from your diet. Vitamin A is a family of molecules that contain a 20-carbon structure with a methyl-substituted cyclohexenyl ring (beta-ionone ring) and a tetraene side chain with a hydroxyl group (retinol), an aldehyde group (retinian), a carboxylic acid group (retinoic acid) or an ester group (retinyl ester) on carbon-15.The Recommended Dietary Allowance (RDA) for dietary provitamin A carotenoids is 12, 24 and 24 μg for beta carotene, alpha-carotene and beta-cryptoxanthin, respectively. In addition, you can use USDA FoodData Central to check the content of carotenoids without vitamin A activity, such as lycopene, lutein and zeaxanthin.
Vitamin A supplementation in late pregnancy may reduce the incidence of bronchopulmonary dysplasia in newborns. Relative dose response (RDR) is a method that allows the indirect evaluation of the relative adequacy of vitamin A stores in the liver. This vitamin A supplement significantly decreased TSH concentration and thyroid volume compared to placebo. Using this approach, you can determine a daily intake of vitamin A that guarantees adequate vitamin A stores to meet your greatest needs during periods of stress and low vitamin A intake.
Therefore, current dietary patterns appear to provide enough vitamin A to prevent deficiency symptoms, such as night blindness. If you take supplements that contain vitamin A, make sure that your daily intake of food and supplements does not exceed 1.5 mg (1500 µg).