Bách khoa toàn thư - Dinh dưỡng và sức khỏe tốt - Vần U | U ubiquinone See coenzyme q. ulcerative colitis See colitis. ulcers See duodenal ulcer peptic ulcer. ultraviolet light UV light A form of radiant energy that lies between visible light and X rays in the electromagnetic spectrum. ultraviolet light has a shorter wavelength than visible light and therefore has more energy than visible light. in fact uV light can induce chemical reactions in the body and in manufacturing processes. uV light from the sun converts a cholesterol product in the skin called 7-dehydrocholesterol to vitamin D1. Commercial treatment of the plant sterol ergosterol with UV light produces vitamin D2. UV light is used to sterilize milk and foods and has other industrial uses because it can destroy viruses and bacteria. UV light is potentially harmful to eyes and skin. Lifelong exposure increases the risk of cataracts due to damage to the lens of the eye. UV exposure is also implicated in damage to the cornea and the retina. Sunburn is an immediate symptom of the dangers of overexposure to UV light. prolonged exposure to UV light in sunlight can cause premature aging of the skin loss of the skin s elasticity causes wrinkles. Long-term exposure to sunlight can cause rough brownish scaly growth on the skin a precancerous condition called actinic keratosis. Tanning increases the risk of skin cancer the most common type of cancer malignant melanoma is the most serious form. A second type of skin cancer basal cell carcinoma does not spread to other parts of the body and is more prevalent. Above 1 million new cases were diagnosed in 2001. Those at greatest risk are fair-skinned people with light-colored eyes those who have a high incidence of moles or who have a family history of cancer and people who spend long periods of time out of doors. preventing skin cancer involves protection from direct exposure to sunlight. Specialists recommend wearing UV-absorbing sunglasses and using appropriate sunscreen lotion whenever individuals are out in the sun. .
