US-RDA

Significant differences in zinc content occur in potatoes. The zinc content ranges Ifom 1.8 to 10.2 p,g/g FW (Andre et al., 2007 Randhawa et al, 1984 Rivero et al., 2003). Yellow-fleshed potatoes from different cultivars contain zinc in 0.5-4.6 p,g/g FW (Dugo et al., 2004). Zinc is needed for the body s immune system to properly work and is involved in cell division, cell growth, and wound healing. The US RDA is 15-20 mg. 

Biotin is widespread in foods, although its availability is affected somewhat by the presence of binding proteins. Biotin is required in only small amounts. Although US RDA values have not been established, the estimated safe and adequate intake of biotin is 30-100 g day -1 for adults. The Department of Health (1991) suggested that biotin intakes between 10 and 200 iig day-1 are safe and adequate. Biotin is reported to be non-toxic in amounts up to at least 10 mg day-1. 

The best food sources of vitamin E are vegetable oils, green leafy vegetables, whole grains, seeds and nuts. Almonds and hazelnuts contain 8.S-9.5 a-tocopherol equivalents per 40g serving, for an impressive 100% of the FDA s proposed reference daily intake (formerly US RDA). 

The alternative approach to determining requirements is to estimate the total body content of vitamin C, then measure the rate at which it is metabolized, by giving a test dose of radioactive vitamin. This is the basis of both the 1989 US RDA of 60 mg/ day for adults and the Netherlands RDA of 80 mg/day. Indeed, it also provides an alternative basis for the RNI of 40 mg/day adopted in Britain in 1991. 

An intake of 40 mg/day is more than adequate to maintain a total body content of 900 mg of vitamin C - the same as the British RNI. At a higher level of habitual intake, 60 mg/day is adequate to maintain a total body content of 1500 mg (the 1989 US RDA). Making allowances for changes in the rate of metabolism with different levels of intake, and allowing for incomplete absorption of the vitamin gives the Netherlands RDA of 80 mg/day. 

The 2000 US RDA for vitamin C, shown in Table 11.3, is based on intakes required to achieve near-complete saturation of neutrophils with the vitamin, with minimal... 

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