- Oral contraceptive (OC) users frequently have lower vitamin B₆
status than non-oral contraceptive (NOC) users. However, normal dietary
intake, a possible factor, has not been adequately studied.
Therefore, 26 OC users and 25 NOC users, of college age, were compared
with respect to dietary intake of vitamin B₆ and blood vitamin B₆
levels. OC users had been taking "the pill" for at least five months
and NOC users had not taken any estrogen-progestin hormones for at
least five months. A 72-hour continuous dietary intake record, kept
by each subject, was used to calculate intakes of vitamin B₆ and nine
other nutrients. Subjects consumed self-selected diets and none had
used vitamin B₆ supplements within two weeks of this study.
Intakes of all nutrients studied were comparable between the two
groups. The mean intakes exceeded the recommended dietary allowance
(RDA) for all nutrients except iron, calories and vitamin B₆. The mean
intake of vitamin B₆ (1.4 [plus or minus] 0.5 mg/day for OC and 1.6 [plus or minus] 0.5 mg/day for
NOC) did not differ significantly between the two groups. The RDA for
this age group is 2.0 mg/day of vitamin B₆. The mean protein intakes
were not significantly different for OC versus NOC users (72.6 [plus or minus] 19.4
g/day for OC and 66.9 [plus or minus] 13.6 g/day for NOC). The ratio of vitamin B₆
to protein was calculated for each subject. Mean ratios were 0.020 [plus or minus]
0.004 for OC and 0.025 [plus or minus] 0.01 for NOC users. This difference was significant
at p<0.05. The mean ratio for both groups exceeded 0.019,
which is considered to be adequate.
Fasting blood samples were collected during the luteal phase (NOC)
or after seven days of the pill cycle for 0C users. These samples
were analyzed for whole blood and plasma (by Lind, 1980) vitamin B₆,
using a microbiological assay (S.uvarum). These values were used to
calculate vitamin B₆ levels in the red blood cell (RBC). A significant
difference (p [less than or equal to] 0.05) was found between the mean level of RBC vitamin
B₆ in the 0C users versus the NOC (12.4 [plus or minus] 5.4 ng/ml for 0C and
16.8 [plus or minus] 8.5 ng/ml for NOC). Plasma vitamin B₆ concentrations
were also significantly different between the two groups. The mean
ratio of plasma vitamin B₆ to RBC vitamin B₆ was not statistically
different between 0C and NOC users.
A questionnaire was used to compare the subject groups with respect to exercise, alcohol intake, general health, general vitamin B₆
intake and other indices. With the exception of alcohol intake, the
mean scores for both groups, from this questionnaire, were similar. 0C
users had a significantly higher intake of alcohol than NOC users, as
measured by the questionnaire. However, the actual alcohol intake from
the dietary record did not differ statistically between the two groups.
The lack of a significant difference in vitamin B₆ intake, coupled
with significantly different blood vitamin B₆ levels for 0C versus NOC
users, tends to indicate that the 0C may be altering vitamin B₆ metabolism.
Estrogens may cause a redistribution of vitamin B₆ in various
body pools, with the vitamin leaving the blood and entering other tissues.
Blood levels are generally used to determine vitamin status. By
this assessment, 0C users have a lower vitamin B₆ status than controls.
It is recommended that 0C users be encouraged to consume at least 2.0
mg/day of vitamin B₆ in their normal diets.