Requirements and Reference Intakes

/Ctmadian report (Institute of Medicine, 1997) discussed requirements only in terms of bone density and medntenance of a plasma concentration of calcitriol above that tissociated with elevated peuathyroid hormone and alkcdine phosphatase. Vieth (1999) noted that intakes above 5 fig per day tue required to prevent osteoporosis (Section 3.4.3) and secondary hyperparathyroidism, emd suggested that normal sunlight exposure may provide the 

Food and Agriculture, Health Organization. Organization WHO, World 

Dietary vitamin D makes little contribution to status, and the major factor is exposure to sunlight, a conclusion that is supported by the two-fold seasonal variation in plasma calcidiol in temperate regions (see Table 3.2). There are no reference intakes for young adults in the United Kingdom and Europe for house-bound elderly people, the reference intake is 10 /rg per day, based on the intake required to maintain a plasma concentration of calcidiol of 20 nmol per L (see Table 3.5). This will almost certainly require supplements of the vitamin, because average intakes are less than half this amount. The U.S./Canadian adequate intake is 5 /xg per day up to age 50, increasing to 10 /xg between 51 to 70, and 15 /xg over 70 years of age (Institute of Medicine, 1997). 

A number of studies have suggested that the cholecalciferol content of human mUk is inadequate to meet the requirements of hreast-fed infants without exposure to sunlight, especially during the winter, when the mother s reserves of the vitamin are low. Infant formulae normally provide 10 /xg of cholecalciferol per day, and a similar amount is recommended for hreast-fed infants. Supplements of 10 /xg per day are also recommended for children between 3 months and 3 years, because of the relatively high requirement during the phase of maximum bone development and the limited exposure to sunlight in temperate regions. Such supplements maintain the plasma concentration of calcidiol above 20 mnol per L. 

Food and Agriculture, Flealth Organization. Organization WFIO, World  

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Levine and coworkers (1995, 1999) have argued that setting requirements and reference intakes on the basis of the steep part of a sigmoidal curve is undesirable. They suggested that a more appropriate point would be where the plasma concentration reaches a plateau, at an intake of around 100 to... 

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