In the absence of adequate exposure to sunlight or equivalent light, dietary intake of vitamin D is required for maintenance of health. Vitamin D occurs naturally in fish and fish oils, eggs, liver and dairy products. The amounts naturally present in dairy products are generally inadequate to meet the requirements and vitamin D3 is added to evaporated milk, infant formulas, and to most fresh fluid cow milk solid by dairies. In addition, vitamin D2 or vitamin D3 is commonly added to margarines, to certain breakfast cereals and to a few other foods. Fortification of milk with vitamin D3 since the 1920s has been credited with the marked reduction in incidence of rickets.
The estimated requirement for vitamin D in the absence of exposure to ultraviolet light is believed to be 100 to 200 IU per day and the Recommended Dietary Allowance of the Food and Nutrition Board, National Research Council, is 400 IU per day. From food sources of vitamin D (naturally occurring or added) it is unlikely that an infant would receive more than 1000 IU per day (perhaps 200 IU per kg per day), a preschool child more than 2000 IU per day (less than 200 IU per kg per day) or an adult more than 5000 IU per day (less than 100 IU per kg per day). However, better estimates of current intakes of vitamin D from dietary sources should, in due course, be developed.
Unequivocal manifestations of vitamin D toxicity including vascular effects have not been reported from consumption of foods including foods fortified with the vitamin. Observations on patients undergoing vitamin D therapy have shown that intakes of vitamin D 1000 IU per kg per day or more (at least 60,000 IU per day for a 60kg adult) have in some instances been associated with evidence of toxicity. Studies of individuals with disorders qualifying them for disability pensions suggest that long-term ingestion of vitamin D in excess of 1000 IU per day may be a factor in the occurrence of myocardial infarction. However, for the adult there is relatively little likelihood of consumption of such amounts of vitamin D from that currently added to food.
The only suggestions that toxic effects may be produced by intakes of vitamin D less than 1000 IU per kg per day concern two special problems of infants: (1) such intakes may interfere with linear growth, and (2) the rare disorder, idiopathic hypercalcemia, may be caused by or aggravated by such intakes. For reasons detailed in the body of this report, the Select Committee finds unconvincing the few reports which attribute interference in linear growth to intakes of vitamin D less than 1000 IU per kg per day. The incidence of idiopathic hypercalcemia is estimated to be 1 in 20,000 births for all forms of the disorder and 1 in 275,000 births for the severe form. This incidence is low must be considered in relation to the demonstrated desirability of fortifying foods with vitamin D. The Committee recognizes also that vitamin D intake may aggravate the manifestations of idiopathic hypercalcemia but considers it unlikely that there is a casual relationship.
At the same time, it is evident that the margin of safety between intakes currently achieved by some infants from all sources (perhaps 200 IU per kg per day) and the amounts (1000 to 3000 IU per kg per day) that may produce toxic manifestations in otherwise normal infants is relatively low. There is strikingly little information on the effects of moderate overdoses of vitamin D, particularly in the range of about 200 to 3000 IU per kg per day for all age groups. Additional data are needed for evaluation of the safety of vitamin D in this dosage range. Moreover, evaluations should recognize that relatively long periods are required for adverse effects of vitamin D to become recognizable. Thus, there appears to be need to limit intakes of vitamin D from all sources, including food and vitamin preparations.
In light of these considerations the Select Committee concludes that: There is no evidence in the available information on vitamin D2 and vitamin D3 that demonstrates or suggests reasonable grounds to suspect a hazard to the public when they are used in food at levels that are now current and in the manner now practiced. However, it is not possible to determine, without additional data, whether a significant increase in consumption would constitute a dietary hazard.