Vitamin D comes in two forms for humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is synthesized by plants, while vitamin D3 is synthesized by humans when our skin is exposed to ultraviolet-B (UVB) rays from the sun. That’s why it’s often called the “sunshine” vitamin. Foods can be fortified with both forms. A significant vitamin D deficiency can result in rickets in children and osteoporosis in adults.
What does it do?
The primary function of vitamin D is to maintain normal blood levels of calcium and phosphorous, thus promoting normal bone formation. Vitamin D also helps regulate the immune system. It has been linked to maintaining a healthy body weight, the reduction of asthma symptoms—both in severity and frequency, and a reduced risk of developing rheumatoid arthritis in women. Perhaps most importantly, recent studies have shown that people who have maintained adequate levels of vitamin D over long periods have a significantly lower risk of developing cancer compared with people with chronically low levels.
Where do I find it?
Vitamin D is found in many dairy products, such as cheese, butter, cream and fortified milk. It is also found in fatty fish, such as salmon and mackerel, oysters and fortified cereals.
How much do I need?
According to the experts, 10-15 minutes of sunshine at least three times weekly is enough to meet the requirement of vitamin D for most people. Keep in mind that in order for the body to manufacture vitamin D, the sun needs to fall on significant areas of skin—such as the face, arms and legs—not covered by sunscreen. Because sun exposure increases your risk for skin cancer, may health experts recommend getting your daily dose of vitamin D during the off-peak hours (before 10am and after 3pm).
People who do not live in sunny places, who have dark-colored skin or who spend most of their time indoors, as well as elderly people, may need to take a vitamin D supplement. Remember, skin exposed to sunlight through a window doesn’t produce vitamin D.
My children’s pediatrician recommends 400-800 IU per day. My father, who lives in the Pacific Northwest, has been advised to take between 2,000 and 4,000 IU daily. In general, people over age 50 need higher amounts of vitamin D than younger people. Be sure to ask your health care provider which amount you should be taking.