APA Dictionary of Psychology

a fat-soluble vitamin with roles in calcium absorption, bone growth and repair, cell growth, and immune function. Its synthesis in humans is triggered by sunlight, and it can be obtained in the diet through some foods, such as fatty fish, in which it appears naturally, and in other foods, such as breakfast cereals, juices, and yogurt, in which it has been added. Vitamin D deficiency can lead to softening of the bones, as in rickets in childhood and osteomalacia in adulthood. It is also associated with multiple sclerosis, some cancers, and diabetes mellitus. Vitamin D supplementation is recommended for anyone at risk for a deficiency, including breastfed infants, people at risk for osteoporosis, and those with dark skin (whose melanin limits sun-triggered vitamin D synthesis). The appropriate daily supplement varies according to age, health status, diet, and other considerations. Excessive intake of vitamin D can be toxic, causing a buildup of calcium in the blood that may result in liver or kidney damage.