How Much Vitamin D?
Vitamin D is a fat soluble vitamin that is stored in the body's fatty tissue. Vitamin D is used by the body to aid the absorption of calcium and to maintain the proper balance of calcium and phosphorus in the blood.
Food sources of vitamin D include dairy products, fish, oysters, fortified cereals, and margarine. Deficiency of vitamin D can lead to osteoporosis in adults or rickets in children. If you consume too much vitamin D, high levels of calcium in the blood may result and cause calcium deposits in soft tissues including the heart and lungs. Other effects of too much calcium include kidney stones, vomiting, and muscle weakness.
Adequate intake of vitamin D depends on age, gender, and other factors. Dietary Reference Intakes (DRIs) have been developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academy of Sciences. Recommended Dietary Allowances (RDA) indicate the average daily level of intake needed to meet the nutritional requirements of nearly all healthy people, according to the National Institutes of Health.
Intake of vitamin D is listed in micrograms (mcg) and International Units (IU). Recommendations are based on the assumption that the vitamin is not synthesized by exposure to sunlight (NIH 2008). For adults age 19-70 years, the adequate intake is 15 mcg or 600 IU; 71+ years 20 mcg or 800 IU. Women who are pregnant or nursing should consume 15 mcg as well.
NIH notes that most people meet their needs of vitamin D through exposure to sunlight. Some suggest that exposure of 5 to 30 minutes of sunshine at least twice a week to the face, arms, legs, or back without sunscreen usually leads to sufficient vitamin D synthesis by the body. Other scientists believe that more vitamin D is needed for optimal health.