Accidental overdoses of liquid vitamin D in infants have been reported. The overdoses have occurred because some packages of liquid vitamin D come with droppers that have room for more liquid than the recommended dose of 400 international units (IU). The 400-IU dose is recommended by the American Academy of Pediatrics for both breastfed and partially breastfed infants. Older children may receive higher doses. The Food and Drug Administration (FDA) has notified manufacturers that they are to clearly mark how much of the dropper provides 400 IU, or change the dropper altogether if the liquid vitamin D is intended for infants, so that it can't hold more than this amount.

Because vitamin D promotes the absorption of calcium, high doses of vitamin D result in high calcium levels. High calcium levels result, as an FDA letter to the industry put it, in "weakness, fatigue, lassitude, headache, nausea, vomiting, and diarrhea." In addition,

mental status changes and coma may also develop. Renal function may be affected early. Cardiac arrhythmias may also ensue. Prolonged hypercalcemia can lead to soft tissue deposition of calcium; favored areas include the kidney, resulting in other associated problems such as hypertension. Additionally, other soft tissues that are affected include blood vessels, heart, lungs, and skin. Osteomalacia may also occur. Blood chemistry changes include elevated calcium and urea, with inconsistent elevation of phosphorus. If the problem is caught early, treatment may completely reverse the symptoms. Residual sequelae may include permanent renal impairment, and osteoporosis, among others.

Nurses should teach parents to measure an infant's dose of vitamin D closely and not to exceed 400 IU per day. If the parent has a product with a dropper that doesn't clearly indicate the 400 IU dose, the product shouldn't be used and a revised product that's in accord with the new safety guidelines should be purchased.