Vitamin D is vital for calcium absorption in bones and to improve muscle strength. Not getting enough vitamin D in childhood can slow growth or cause misshapen bones (rickets), and not getting enough vitamin D throughout life increases the risk for bone thinning (osteoporosis) in later years.

Many people can get the amount of vitamin D needed each day through food and sunlight. Vitamin D is in foods such as egg yolks, liver, saltwater fish, and vitamin D-fortified dairy products. Vitamin D also is available in supplements, often in combination with calcium.