Retinoids retinol, retinal, and retinoic acid - 3 active forms of vitamin A - "preformed" vitamin A.
Beta carotene can easily be converted to vitamin A by the human body.
Large amounts of supplemental vitamin A (but not beta carotene) can be harmful to bones.
Vitamin A keeps tissues and skin healthy, plays an important role in bone growth. Diets rich in the carotenoids alpha carotene and lycopene seem to lower lung cancer risk. Carotenoids act as antioxidants. Foods rich in the carotenoids lutein and zeaxanthin may protect against cataracts. Essential for vision lycopene may lower prostate cancer risk.
Recommended daily amount: 700 mcg - 900 mcg or 3 mg - 6 mg beta-carotene (~ 1 cup of raw cantaloupe or sweet red peppers, or 2 mangoes, or 1/5 of one baked sweet potato).
Because the body converts all dietary sources of vitamin A into retinol, 1 mcg of physiologically available retinol is equivalent to the following amounts from dietary sources: 1 mcg of retinol, 12 mcg of beta-carotene, and 24 mcg of alpha-carotene or beta-cryptoxanthin. From dietary supplements, the body converts 2 mcg of beta-carotene to 1 mcg of retinol.
What do they know-all these scholars, all these philosophers, all the leaders of the world - about such as you? They have convinced themselves that man, the worst transgressor of all the species, is the crown of creation. All other creatures were created merely to provide him with food, pelts, to be tormented, exterminated.
Vitamins are a group of substances that are needed for normal cell function, growth, and development. There are 13 essential vitamins:
Vitamin A (retinol, retinal, 4 carotenoids)
Vitamin C (ascorbic acid)
Vitamin D (D3 - Cholecalciferol, D2 - Ergocalciferol)
Vitamin E (tocopherols, tocotrienols)
Vitamin K (phylloquinone, menaquinones)
Vitamin B1 (thiamine)
Vitamin B2 (riboflavin)
Vitamin B3 (niacin)
Vitamin B5 (pantothenic acid)
Vitamin B6 (pyridoxine, pyridoxal, pyridoxamine)
Vitamin B7 (biotin)
Vitamin B9 (folic acid)
Vitamin B12 (cyanocobalamin)
Fat-soluble vitamins are stored in the body's fatty tissue: vitamins A, D, E, K.
Water-soluble vitamins - the body must use almost all water-soluble vitamins right away - vitamins B1, B2, B3, B5, B6, B7, B9 and C. Vitamin B12 is the only water-soluble vitamin that can be stored in the liver for many years.