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.
A virus is a small infectious agent that replicates only inside the living cells of other organisms. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.
There are millions types of viruses, ~ 5,000 virus species have been described in detail. Viruses are found in almost every ecosystem and are the most abundant type of biological entity. The origins of viruses in the evolutionary history of life are unclear.
While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent particles, virions, which consist of the genetic material made from either DNA or RNA, a protein coat, and in some cases an outer coat of lipids. Virion is about one one-hundredth the size of a bacterium.