| Summary: | Previous studies have found that smoking may have a negative effect on
vitamin B-6 indices and have demonstrated a possible association between smoking
and depressed plasma pyridoxal-5'-phosphate (PLP) concentration. Individuals with
plasma PLP values below the adequate level of 30 nmoles/L might benefit from
consumption of vitamin B-6 supplements, but no data are available on vitamin B-6
status in smokers consuming a controlled vitamin B-6 intake and receiving a vitamin
B-6 supplement. The objectives of this research were to assess vitamin B-6 status in
smokers as compared to non-smokers receiving a controlled diet and to evaluate the
effect of an oral vitamin B-6 supplementation in these subjects.
The vitamin B-6 (B-6) status of 5 (four males / one female) smokers (S) and 4
(three males / one female) non-smokers (NS) was assessed. A constant diet was fed
for 20 days and provided 1.95 mg of B-6 or 1.65 mg of B-6 for males and females,
respectively. For the last 10 days, an additional 2-mg of pyridoxine (PN) was given
daily. Blood samples were collected on days 1.7, 11.14 and 21; and 24 hour urine samples were collected daily. Urinary 4-pyridoxic acid (4-PA) and total B-6 (UB6)
excretion, plasma B-6 vitamers (PLP, PN, pyridoxal and 4-PA) and red blood cell
PLP (RBC PLP) concentrations, as well as plasma alkaline phosphatase activity
(APA) were determined. Mean plasma PLP, 4-PA, and RBC PLP concentrations
were significantly lower (P [less than or equal to] 0.05) at all time points in S compared to NS. With a
daily supplement of 2-mg vitamin B-6, the mean plasma PLP concentration of S
increased 85.8% but was 48.5% lower than that of NS consuming 1.65-1.95 mg/d of
B-6. Mean plasma pyridoxal concentrations were not different between S and NS
before and after supplementation. Excretion of 4-PA was not significantly different
between S and NS, but the mean values of 4-PA excretion were consistently greater
in NS compared to that of S throughout the 20-day study. The percent of ingested B-6 excreted as 4-PA for the S and NS was 38 and 49 in the non-supplemented period,
and 47 and 53 in the supplemented period, respectively, indicating that non-smokers
excreted more 4-PA than smokers. However, the difference in 4-PA excretion
between S and NS was not significantly different both before and after
supplementation (P>0.05). In addition, there was no significant difference between S
and NS for plasma PN concentration, AP, and UB6 excretion for both periods.
Results suggested an adverse effect of smoking on B-6 metabolism, thus an increased
requirement of vitamin B-6 in smokers. A 2-mg PN supplement was sufficient to
bring the concentration of plasma PLP in smokers to the level suggested as adequate,
but it didn't bring it to the level of non-smokers. === Graduation date: 1999
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