Vitamin D-3, one of two forms of vitamin D used in supplements, does not differ chemically from the form of vitamin D the body produces naturally. Vitamin D-3 may be more effective than vitamin D-2 at boosting blood levels of vitamin D, notes the Harvard School of Public Health. However, it also comes with some health risks.
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Non-specific symptoms of vitamin D toxicity may include anorexia, weight loss, polyuria and abnormal heart rhythms, according to the National Institutes of Health Office of Dietary Supplements. Other symptoms of excessive vitamin D may include weakness, fatigue, headache, dry mouth, metallic taste and nausea, according to MedlinePlus.
Unhealthy Calcium Levels
Long-term use of vitamin D supplements with doses higher than 4,000 units may cause excessively high levels of calcium in the blood, notes MedlinePlus Medical Encyclopedia. High calcium levels can increase the risk for kidney stones and atherosclerosis, or hardening of the arteries. Some individuals may be more vulnerable to vitamin D’s effects on calcium levels, including those who already have high calcium levels and those with sarcoidosis, histoplasmosis, hyperparathyroidism or lymphoma.
While you don't need to worry about your body producing too much vitamin D -- natural checkpoints prevent your body from producing too much -- you do need to be careful about how much supplemental D-3 you take. The Institute of Medicine has established a Tolerable Upper Intake Level for vitamin D of 4,000 international units, or IU, per day for children and adults ages 9 and over. Doses of vitamin D-2 or D-3 higher than 4,000 units should only be taken for short-term treatment with doctor supervision, according to MedlinePlus. Dr. Edward Giovannucci of the Harvard School of Public Health recommends avoiding doses of vitamin D greater than 2,000 IU until further scientific evidence emerges about potential risks. However, short-term intakes of vitamin D below 10,000 IU per day are unlikely to cause symptoms of toxicity, notes the National Institutes of Health Office of Dietary Supplements.
Vitamin D helps the body maintain healthy calcium levels, promoting bone health and reducing the risk for osteoporosis, according to the Harvard School of Public Health. Vitamin D may also play a role in the prevention of heart disease, some cancers, autoimmune diseases such as multiple sclerosis and infectious diseases such as tuberculosis and seasonal flu, according to the Harvard School of Public Health. As with starting any supplements, consult with your physician before adding Vitamin D supplements.