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The Influence of Protein Intake on Vitamin B-6 Metabolism Differs in Young and Elderly Humans¹

Department of Human Biology, University of Limburg, P.O. Box 616, 6200 MD Maastricht, The Netherlands ^* Department of Human Nutrition, TNO Toxicology and Nutrition Institute, P.O. Box 360, 3700 AJ Zeist, The Netherlands

Vitamin B-6 metabolism was studied as a function of dietary protein intake. Subjects were 29 young adults (29 ± 1 y old) and 26 elderly adults (70 ± 1 y old) who consumed standardized diets containing 12% (Diet A) and 21% (Diet B) of total energy as protein for 3 wk each, according to a randomized crossover design. Vitamin B-6 intake for young and elderly subjects was 1.52 ± 0.08 mg/d (21.74 ± 0.45 µg/g protein) and 1.47 ± 0.05 mg/d (23.81 ± 0.08 µg/g protein), respectively, during consumption of Diet A and 1.79 ± 0.07 mg/d (14.49 ± 0.11 µg/g protein) and 1.73 ± 0.05 mg/d (16.24 ± 0.06 µg/g protein) during consumption of Diet B. Plasma pyridoxal phosphate (PLP), pyridoxal and total vitamin B-6 concentrations were significantly lower in the elderly subjects compared with the young adult subjects during both diet periods. In the elderly subjects, PLP was significantly higher during Diet B consumption (Diet A: 27 ± 3 nmol/L; Diet B: 32 ± 3 nmol/L), whereas the level of protein intake had no significant effect on plasma PLP in the young adults (Diet A: 47 ± 6 nmol/L; Diet B: 45 ± 5 nmol/L). Plasma pyridoxal and plasma total vitamin B-6 concentrations were not influenced by the amount of protein intake in young and elderly subjects. Relative urinary pyridoxic acid excretion did not differ significantly between diet periods in the elderly subjects (Diet A: 37 ± 3%; Diet B: 43 ± 3%), whereas pyridoxic acid excretion was lower in young adults when Diet B was consumed (Diet A: 46 ± 3%; Diet B: 38 ± 2%; P < 0.001). The results of this study suggest an age-dependent difference in the protein intake-related vitamin B-6 needs, whereby elderly subjects apparently need less vitamin B-6 at a higher protein intake as compared with young adults.

KEY WORDS: • vitamin B-6 metabolism • protein metabolism • young and elderly humans

¹ 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.

² To whom correspondence and reprint requests should be addressed.

Manuscript received 25 October 1993. Revision accepted 2 March 1994.

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