Vitamin D is a fat-soluble vitamin needed by the body. Vitamin D is essential in the maintenance of calcium and phosphorus levels in the blood. It is necessary to prevent brittle bones and weak muscles. Vitamin D may be obtained from dietary sources, supplements or through exposure to sunlight. Vitamin D requirements increase with age and for those living in areas with limited sunlight. Toxicity is rare, but can result from consuming excessive amounts of vitamin D.
RDA
Recommended dietary allowances for vitamin D have been established by the Institute of Medicine. During infancy through 1 year of age, babies require 400 IU of vitamin D each day. After the first year of life through the age of 70, you need to consume 600 IU of vitamin D per day. The recommended dietary allowance increases after the age of 70 to 800 IU of vitamin D daily. This does not account for the amount of sun exposure.
Dietary Sources
Very few foods contain vitamin D. Fatty fish such as haddock, mackerel, trout, herring, salmon, sardines or tuna, fish liver oils, beef liver and egg yolks are the best sources. Fortified foods provide most of the vitamin D in the typical American diet. Milk, infant formula, ready-to-eat breakfast cereals, bread, yogurt, margarine and even orange juice may be fortified. Vitamin D supplements are also available. Multivitamin supplements typically provide 400 to 2,000 IU of vitamin D. Most calcium supplements contain similar amounts of vitamin D. Intakes of vitamin D from food that are high enough to cause toxicity are very unlikely. Toxicity is much more likely to occur from high intakes of dietary supplements containing vitamin D.
Sun Exposure
Vitamin D is also made in your body after exposure to ultraviolet rays from the sun. Exposure to sunlight is an important source of vitamin D as it triggers the synthesis of vitamin D in the skin. If you spend a short time outside in the sun two to three times per week, you can meet your entire vitamin D requirements. However, this is dependent upon where you live. Excessive sun exposure does not result in vitamin D toxicity. The body has the ability to regulate the amount of vitamin D converted into its active form for absorption.
Tolerable Upper Intake Level
The tolerable upper intake level, or UL, is the level of dietary intake of a vitamin, such as vitamin D, that will not cause toxicity. For infants up to six months, the UL is 1,000 IU and from seven to 12 months it is 1,500 IU of vitamin D daily. Children ages 1 to 3 should not consume more than 2,500 IU and children ages 4 to 8 should not exceed 3,000 IU of vitamin D per day. For individuals over 9 years, the UL is 4,000 IU of vitamin D each day. Long-term intakes above the UL increase the risk of adverse affects related to toxicity. The UL for vitamin D is relatively low as the toxicity threshold is closer to 10,000 IU of vitamin D on average.
Toxicity Symptoms
Excess vitamin D in the body causes abnormally high levels of calcium to form in the blood. The most common symptoms of toxicity include constipation, decreased appetite, excessive thirst, dehydration, fatigue, irritability, muscle weakness, vomiting and heart arrhythmia. Clinical signs include excess calcium in the urine and blood, high blood pressure and increased frequency and urgency of urination. If left untreated, hypervitaminosis D can result in kidney stones, chronic dehydration or damage to the bones, heart and kidneys.
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