Builds and maintains strong teeth and bones; aids calcium absorption; vitamin D and calcium together may help prevent osteoporosis, aid weight loss and improve blood lipid levels; modulates the immune system, which may protect against autoimmune diseases, such as RA; may reduce the risk of breast and colorectal cancers.
How Much: RDA = 200 IU for adults through age 50; 400 IU from 51 to 70 years of age; 600 IU age 70 and older.
Too Much: UL = 2,000 IU (although a 2007 study shows up to 10,000 IU may be safe).
Too Little: A high risk of osteoporosis. Low levels lead to muscle weakness, which can cause older people to tire easily and fall.
Foods: Fortified milk, orange juice and breakfast cereals; egg yolks, butter, salmon, herring, tuna and sardines.
Interactions: Corticosteroids, such as prednisone; antacids that contain magnesium, cholestyramine (Questran); and mineral oil.
Research Note: People with knee osteoarthritis (OA) who increased their daily vitamin D intake gained muscle strength and improved physical function. Daily vitamin D supplements increase calcium absorption by 65 percent, but that benefit can be blocked by consuming more than 300 milligrams (mg) of caffeine per day.
