Aging and the bioavailability of vitamin B-6

Christina Elizabeth Ferroli, Purdue University

Abstract

An age-related decline in vitamin B-6 status has been demonstrated in humans and rodents as indicated by reduced plasma pyridoxal 5$\sp\prime$-phosphate concentration. The cause of the apparent reduced vitamin B-6 status is still elusive. By controlling dietary intake and administering an oral dose of deuterium labeled pyridoxine, (d2)PN, this study's goal was to conclusively determine whether diet or altered metabolism of vitamin B-6 is the cause of marginal vitamin B-6 status in elderly people. Healthy males between 20-30 and 60-70 years of age consumed the same foods for each meal for five consecutive days. Two days after initiation of the study, blood was collected and subjects were given an oral dose of (d2)PN. Twenty-four hour urine samples were collected for the remaining three days of the study. No differences were observed in plasma pyridoxal 5$\sp\prime$-phosphate concentration, erythrocyte aspartate amino transferase activity, or plasma alkaline phosphatase activity between the two age groups. Dietary vitamin B-6 excreted as (d2)4-pyridoxic acid did not differ significantly between the two age groups over the 3-day period. These results indicate that vitamin B-6 status and bioavailability is not altered with aging in non-institutionalized, healthy adult males. The bioavailability of vitamin B-6 in 3- and 20-month-old Fischer 344 rats was evaluated by administration of a single, oral dose of ($\sp3$H) pyridoxine. Plasma pyridoxal 5$\sp\prime$-phosphate concentration was 75% lower in the aged rats compared with the 3-month-old rats. Plasma alkaline phosphatase activity was reduced and erythrocyte aspartate aminotransferase activity increased in the aged rats, however, neither were significantly different. There was no difference in erythrocyte aspartate aminotransferase stimulation for both age groups. No differences were observed in tissue distribution of B-6 ($\sp3$H) vitamers between the two age groups or in the retention of radioactivity by the various tissues examined. Urinary excretion of ($\sp3$H) vitamin B-6, as well as ($\sp3$H) 4-pyridoxic acid was not different between the two age groups. Reduced plasma pyridoxal 5$\sp\prime$-phosphate concentration with aging does not appear to be the result of decreased intestinal absorption of vitamin B-6, increased plasma alkaline phosphatase activity, or altered metabolic utilization of vitamin B-6.

Degree

Ph.D.

Advisors

Trumbo, Purdue University.

Subject Area

Nutrition

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