Vitamin A is a generic term describing compounds that have the same biological activity as retinol. Dietary vitamin A can be obtained from "provitamin A" carotenoids (e.g., ß-carotene) found in plant foods such as carrots, cantaloupes, and sweet peppers, or as "preformed vitamin A" found in many dietary supplements, animal livers, and vitamin A-fortified foods, such as breakfast cereals, milk, cheese, and yogurt. Low consumption of vitamin A can cause night blindness, reduce immune function, and have detrimental developmental effects. Several lines of evidence suggest that excessive dietary intake of vitamin A might be associated with an increased risk of bone fractures. Meta-analysis of observational human studies that have examined vitamin A and fractures suggests that dietary consumption of large amounts of vitamin A in the form of ß-carotene likely has a protective effect, reducing the risk of fractures. On the other hand, meta-analyses that have specifically examined hip fractures have shown that total vitamin A (all types) or retinol consumption may increase the risk of hip fractures. Until more information is available, it is advisable to consume vitamin A primarily from plant sources, avoid excessive consumption from dietary supplements and animal sources, and lower consumption from fortified foods.