A tree is a plant with an elongated stem, or trunk, supporting branches and leaves in most species. Trees tend to be long-lived, some reaching several thousand years old. Trees have been in existence for 370 million years.
A variety of plant species have independently evolved a woody trunk and branches to compete for sunlight. In more general sense, tall palms, tree ferns, bananas and bamboos are also trees. The roots branch out under the ground to anchor the tree and to extract moisture and nutrients from the soil. Above ground, the branches usually bear leaves, which capture light.
Trees reduce erosion and moderate the climate. Trees and forests provide a habitat for many species of animals and plants. Some trees provide edible fruit.
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.