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FIGURE 7-1 The relationships between (A) plasma pyridoxal phosphate (PLP) concentrations and vitamin B6 intake per gram of dietary protein and (B) plasma PLP concentrations and B6 intake. Data derived from a compilation by J.Leklem, Oregon State University and from Hansen et al. (1997), Huang et al. (1998), Kretsch et al. (1995), and Ribaya-Mercado et al. (1991).

tors in women receiving high-dose oral contraceptives (Rose, 1978; Shane and Contractor, 1975). Plasma PLP concentrations are decreased but the decrease is quite small. Normalization of the tryptophan load test in subjects receiving oral contraceptives requires very high levels of PN, up to 25 mg (Rose, 1978). This probably reflects hormonal stimulation of tryptophan catabolism rather than any deficiency of B6 per se. These studies were conducted when the

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