Vitamin D helps your body absorb calcium. Calcium is one of the main building blocks of bone. A lack of vitamin D can lead to bone diseases such as osteoporosis or rickets. Vitamin D also has a role in your nerve, muscle, and immune systems.

You can get vitamin D in three ways: through your skin, from your diet, and from supplements. Your body forms vitamin D naturally after exposure to sunlight. However, too much sun exposure can lead to skin aging and skin cancer. So many people try to get their vitamin D from other sources.

Vitamin D-rich foods include egg yolks, saltwater fish, and liver. Some other foods, like milk and cereal, often have added vitamin D.

You can also take vitamin D supplements. Check with your health care provider to see how much you should take. People who might need extra vitamin D include

• Seniors
• Breastfed infants
• People with dark skin
• People with certain conditions, such as liver diseases, cystic fibrosis and Crohn's disease
• People who are obese or have had gastric bypass surgery

NIH: National Institutes of Health Office of Dietary Supplements