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Vitamin B-6 Status of Women with a Constant Intake of Vitamin B-6 Changes with Three Levels of Dietary Protein^1,2,3,4,

Department of Nutrition and Food Management, Oregon State University, Corvallis, OR 97331

To determine the effect of varying levels of dietary protein with a constant intake of vitamin B-6 (B-6) on B-6 status, nine women were fed diets providing daily intakes of 1.25 mg B-6 and 0.5, 1.0 and 2.0 g protein/kg body weight. After an 8-d adjustment period, the women consumed each level of dietary protein for 14 d in a Latin-square design. Several direct and indirect B-6 status indicators were measured in blood and urine. Significant differences among protein levels were found for urinary 4-pyridoxic acid (4-PA) excretion (P < 0.01), plasma pyridoxal 5'-phosphate (PLP) concentration (P < 0.05), and urinary excretion of volatile amines (VA, kynurenine plus acetylkynurenine) after a 2-g L-tryptophan load (P < 0.05). Nitrogen intake was significantly negatively correlated with urinary 4-PA excretion (r = -0.619, P < 0.001) and plasma PLP concentration (r = -0.549, P < 0.01), and positively correlated with erythrocyte alanine aminotransferase percentage stimulation (r = 0.418, P < 0.05) and urinary post-tryptophan load excretion of xanthurenic acid (r = 0.535, P < 0.05), kynurenic acid (r = 0.563, P < 0.05) and VA (r = 0.626, P < 0.01). Compared with men consuming diets with similar B-6 to protein ratios in a previous study, the women excreted a greater percentage of the B-6 intake as 4-PA, had lower plasma PLP concentrations and excreted greater amounts of postload urinary tryptophan metabolites at all three protein levels. If the Recommended Dietary Allowance (RDA) of vitamin B-6 is to be based on the dietary B-6 to protein ratio, gender differences in response to varying protein intakes should be considered. For the levels of protein intake used in this study and a B-6 intake of 1.25 mg/d, a B-6 to protein ratio of greater than 0.020 mg/g is required for adequate vitamin B-6 status in women.

KEY WORDS: • vitamin B-6 • protein intake • status • requirements • women

¹ Presented in part at Experimental Biology 91 and 93 [Leklem, J., Hansen, C. & Miller, L. (1991) Effect of three levels of protein on vitamin B-6 status of adult women, FASEB J. 5:A557 (abs.) and Leklem, J., Hansen, C., Hardin, K. & Miller, L. (1993) Vitamin B-6 status and tryptophan metabolism in young women fed diets of varying B-6 to protein ratios, FASEB J. 7:A744 (abs.)].

² Supported by U.S. Department of Agriculture grant no. 88-37200-3520.

³ Paper no. 10,871 from Oregon Agricultural Experiment Station.

⁴ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁵ To whom correspondence and reprint requests should be addressed.

Manuscript received 7 December 1995. Revision accepted 3 April 1996.

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