American Journal of Clinical Nutrition, Vol 24, 1028-1041, Copyright © 1971 by The American Society for Clinical Nutrition, Inc.

Vitamin B₆ requirement of young adult women

¹ Associate Professor, School of Household Economics, The University of Alberta, Edmonton 7, Alberta, Canada
² Trace Research Laboratory, Veterans Administration Hospital, Washington, D. C.
³ Dalhousie University, Halifax, Nova Scotia, Canada
⁴ Nutritionist, Jersey Shore Medical Center, Neptune, New Jersey
⁵ Department of Environmental Medicine and Community Health, Downstate Medical Center, Brooklyn, New York

Eight young adult women served as subjects on a metabolic study to assess the vitamin B₆ needs for this particular group. They ranged in age from 21 to 30 years and in weight from 114 to 138 lb. All subjects were judged to be healthy both before and after completing the study. For 43 days they consumed a natural food diet, nutritionally adequate except that it contained only 0.34 mg vitamin B₆. This was followed by supplementation with 0.6 mg PIN-HCl for 7 days; 1.2 mg for 3 days, and 30.0 mg for 1 day. Twenty-four-hour urine collections were made, pooled into 4-day composites, and analyzed for creatinine, 4-PDA, and vitamin B₆ content. Periodic blood samples were taken and were analyzed for vitamin B₆, GOT and GPT levels in the erythrocyte, and amino acid levels in the plasma.

Subjects were requested to maintain their initial body weight by consuming a basal diet plus ad libitum foods that supplied additional calories from fat and carbohydrate. All subjects lost weight during the depletion phase in spite of an increasingly greater caloric intake. Mean kilocalories per pound of body weight increased from 13.9 to 17.8 during the depletion phase of the study. The difference in kilocalories per pound of body weight for the first 8 days of the study compared with the 7 days immediately prior to repletion was significant at a P < 0.01. Although there was an initial decrease in calorie consumption immediately after starting each level of supplementation, there appeared to be no lasting effect of the added PIN-HCl.

During the depletion phase the amount of 4-PDA and vitamin B₆ excreted in the urine decreased significantly. The levels of each metabolite increased with the supplementation of the basal diet, which contained 0.34 mg vitamin B₆, with 0.6, 1.2, and 30.0 mg/day PIN-HCl for 7, 3, and 1 days, respectively. Based on these two indices, it is proposed that the dietary requirement for vitamin B₆ for adult women consuming a moderate protein diet is 1.5 mg/day.

Vitamin B₆ was determined in erythrocytes and after a slight initial rise during the first week of depletion the level of vitamin B₆ gradually dropped to a value that was 14% of the original day 1 values. This occurred 43 days after initiating the depletion phase. Supplementation of the diet with two levels of PIN-HCl resulted in an increased amount of the vitamin in the red blood cell to 75% of the initial level. The consumption of a self-selected diet containing 1.6 mg/day for 10 additional days more than restored the original vitamin levels in the erythrocytes. This would also suggest that an intake of 1.5 mg vitamin B₆ is an adequate intake for young women.

The GOT and GPT levels in the erythrocytes were also studied. Although the GOT level decreased throughout the depletion period, repletion with PIN-HCl failed to restore the level of the enzyme in the cells, thus at the completion of the post-study period only about 65% of the activity of day 1 had been restored. GPT in the erythrocytes did not respond to either depletion of the subject of vitamin B₆ or repletion with the vitamin. As used in this study, the reliability of these methods for the assessment of the need of vitamin B₆ in the human is questioned.

Although an increase in many of the free plasma amino acids was observed throughout the depletion phase, the net change over the total depletion phase was nil, as the free plasma amino acid levels decreased after becoming maximal 29 days after beginning the low vitamin B₆ diet. The same changes were observed in both the essential and nonessential amino acid levels in the plasma, for the E/N ratio remained almost constant throughout the period. The daily administration of 0.6 mg PIN-HCl for 7 days, 1.2 mg daily for 3 days, followed by a 30-mg load dose of l-tryptophan for 1 day, and a self-selected diet for 10 days resulted in an initial increase in plasma amino acid levels again followed by a decrease, so that the levels of the free amino acids in the plasma were somewhat lower at the end of the post-study but not dissimilar to the initial levels. The feeding of a diet low in vitamin B₆ seems to have resulted in a temporary shift of amino acids into the plasma, followed by a return to the original level by the end of the depletion phase. A reversal of the shift that occurred during depletion resulted from the administration of PIN-HCl to the subjects during the repletion phase. Change in the plasma amino acid levels with change in the dietary intake of vitamin B₆ would seem to be dependent upon the length of time that a diet low in the vitamin had been administered.