Your body needs vitamin D to function properly and help prevent certain diseases. However, high doses of vitamin D can become toxic and cause many symptoms and health problems. If you are concerned about your vitamin D intake or are experiencing problems with your eyesight, talk with your physician, who can test your level of vitamin D and make recommendations on how much you really need.
Vitamin D
Getting enough vitamin D is essential to maintain strong bones, as vitamin D must be present in order for the bones to absorb calcium. A severe deficiency of vitamin D can lead to a weakening of the bones, causing rickets in children or osteoporosis in adults. Adults need about 600 to 800 IU of vitamin D every day, which you can obtain by getting 10 to 15 minutes of sunshine each week or by eating foods such as tuna, salmon, mackerel, oysters and fortified foods. As important as vitamin D is, taking too much can cause the body to retain more calcium than it needs, so supplements should be used only under a doctor's care.
Safe Upper Limits
Before taking a vitamin D supplement, your physician can run tests to see what your vitamin D level is. Deficiencies are common because there are very few foods that are good sources. While the RDA is about 800 IU a day, doctors may prescribe taking 1,000 to 5,000 units of vitamin D-3 once a day, or 50,000 units of vitamin D-2 once or twice a week, notes the Cleveland Clinic. These higher doses can help to correct a deficiency, but they cannot be taken for long, as your level can get too high. Your physician can test your blood regularly to prevent complications related to vitamin D toxicity.
Vitamin D Overdose
Too high a level of vitamin D is called hypervitaminosis D, and it can have serious complications. Changes in eyesight are not a common symptom, but ones that are include nausea, vomiting, poor appetite, constipation, weakness, confusion, heart rhythm abnormalities and kidney stones, reports MayoClinic.com. Most of these symptoms are not from the vitamin D, but rather from the buildup of calcium that too much vitamin D causes. Having an underlying kidney or liver condition raises your risk of complications from too much vitamin D.
Treatment
In severe cases, too much vitamin D can lead to anorexia, dehydration and high blood pressure. If high blood pressure affects the blood vessels that supply your eyes, you may experience changes in your vision. If hypervitaminosis D occurs, you may need to stop taking supplements, reduce your intake of calcium or take medication. Most cases of hypervitaminosis D are due to taking high doses of prescription-strength vitamin D, but recovery can be complete with the proper treatment, reports the University of Tennessee Medical Center.
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