Upper level vitamin

Abnormal accumulation in tissues and overloading of normal metabolic pathways, leading to signs of toxicity and possibly irreversible lesions. Niacin (Section 8.7.1), and vitamins A (Section 2.5.1), D (Section 3.6.1), and Bg (Section 9.6.4) are all known to be toxic in excess (see Section 1.2.4.3 for a discussion of tolerable upper levels of intake). 

Tolerable Upper Levels of Intake A number of the vitamins are known to be toxic in excess. For most, there is a considerable difference between reference intakes that are more than adequate to meet requirements and the intake at which there may he adverse effects, although for vitamins A (Section 2.5.1) and D (Section 3.6.1) there is only a relatively small margin of safety. 

Table 1.10 shows the NOAEL for the vitamins, the upper limits for supplements available over the counter proposed by the European Eederation of Health Product Manufacturers Associations (Shrimpton, 1997), the U.S./ Canadian tolerable upper levels, and the prudent upper levels of consumption from the EU tables. 

Sources Shrimpton, 1997 Institute of Medicine, 1997, 1998, 2000, 2001 Scientific Committee for Food, 1993 where two figures are shown for vitamin A, the lower is for women and the higher is for men (Table 2.5). for niacin and nicotinic acid, the lower values are for sustained reiease preparations the EU upper level of 25 mg of vitamin Be was proposed by the Scientific Committee for Food Opinion, 2000 and the EU upper level of 200 xg of vitamin B12 was set because of the possible presence of inactive corrinoids in pharmaceutical preparations, not because of toxicity of the vitamin itself. 

Table 2.5 Prudent Upper Levels of Habitual Intake (jjug of preformed vitamin A/day)...

The U.S./Canadian tolerable upper level is set at 1,000 mg per day, based on reports of prolonged prothrombin time in people receiving anticoagulants and consuming 1,100 to 2,100 mg of vitamin E per day. It is noteworthy that although the report specifically excluded the 2S isomers of synthetic a-tocopherol from calculations of nutritional requirements, this tolerable upper level includes all forms of the vitamin, regardless of their tissue retention and biological activity (Institute of Medicine, 2000). 

Regardless of whether or not high intakes of ascorbate have any beneficial effects, large numbers of people habitually take between 1 to 5 g per day of vitamin C supplements, and some take considerably more. The U.S. /Canadian tolerable upper level of intake is 2 g per day (Institute of Medicine, 2000). 

Upper Levels of Vitamin Be Intake Although there is no doubt... 

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