Vitamin D is known as the "sunshine" vitamin because we synthesize it from sunlight that touches our skin. This essential nutrient is important for regulating bone metabolism, insulin sensitivity and immune function, the Office of Dietary Supplements notes. The current Adequate Intake (AI) of vitamin D as determined by the Institute of Medicine is 200 international units (IU) per day for adults under age 50, and 400 IU for adults 50 and older. However, these recommendations are under review by the Institute of Medicine in light of new research suggesting that the current recommendations may not be enough, Harvard University reports. However, although rare, side effects of vitamin D toxicity are serious.
Blood Calcium
Registered dietitian Katherine Zeratsky of the Mayo Clinic reports that the majority of vitamin D toxicity cases occur from excessive supplementation. Because vitamin D's chief role is to help it absorb and preserve calcium, excess vitamin D can result in too much calcium in the blood. This is known as hypercalcemia. Hypercalcemia is the underlying cause of many of side effects of excess vitamin D.
Stomach upset
Hypercalcemia can lead to problems with the gastrointestinal tract including vomiting, stomach upset, constipation and loss of appetite. Over time, this can lead to unplanned weight loss.
Heart
Blood calcium is an important regulator of the heart's rhythm. If it gets too high, the heart beats abnormally. Known as arrhythmia, this condition can lead to fainting and even sudden death.
Kidneys
All that extra calcium in the blood forces the kidneys to filter out more than they're designed to. Supplementing with vitamin D and calcium increases the risk of kidney stones significantly, notes R.D. Jackson of Ohio State University. A paper published in the February 2006 issue of the "New England Journal of Medicine," said postmenopausal women who took daily calcium and vitamin D supplements had a 17 percent greater risk of kidney stones.
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