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Folate status and dietary folate intake of women during oral contraceptive use and pregnancy

University of British Columbia

During pregnancy, the expansion of fetal and maternal tissues increases the demand for folic acid and may result in reduced levels of serum and red cell folate in the mother. If dietary intake of folate is also poor, maternal folate stores may be further depleted. Recent research has investigated the possibility of a similar alteration in folate status among women using oral contraceptives. Although there have been several reports in the literature demonstrating reduced serum folate concentrations in women taking the pill, other studies have contradicted these findings. Furthermore, it has not been established to what extent dietary folate intake determines the serum or red cell folate levels of women using oral contraceptives. A cross-sectional survey was designed to determine the relationship between dietary folate intake and serum and erythrocyte folate concentrations in women who are pregnant or using oral contraceptives, as compared with a group of control women. In addition, this study was intended to examine any differences or similarities in folate status among the three groups. A sample of 48 women of similar age, parity, and socio-economic status was selected from the Vancouver area. These subjects were classified into three groups: a control group of 18 women, who had neither been pregnant nor using oral contraceptives for at least six months prior to being in the study; an oral contraceptive group of 22 women, all of whom had been taking combination- type oral contraceptives for at least four months prior to being in the study; and a pregnant group of 8 women, who were in their third or fourth month of pregnancy at the time of commencing their participation in the study. All subjects were in good health and were not taking folic acid supplements. Any woman was excluded from the study if she had a condition (other than pregnancy) that might alter folate metabolism, or if she was using a drug (other than oral contraceptives) known to interfere with folate metabolism. For the oral contraceptive users and control women, fasting blood samples were taken at two different phases of the menstrual cycle ---day 5 and day 20--- for two consecutive cycles. In the group of pregnant women, three fasting blood samples were taken, one during each trimester of pregnancy. Each subject also kept two three-day diet records ---one for the three days preceding the first blood sample, and the other for the three days preceding the last blood sample. The mean daily dietary folate intake was calculated from these records using food composition tables. The accuracy of these calculated estimates for folate was tested by assaying food samples collected by 15 of the subjects. Folate was measured microbiologically with Lactobacillus casei. The results indicate that serum folate concentrations were higher in the control group than in the oral contraceptive group. This difference was statistically significant (p<0.05) for the serum folate values at day 5 of the menstrual cycle, but not at day 20 of the cycle. There was no significant difference in the red cell folate levels between these two groups of subjects although, again, the control women had higher levels than did the oral contraceptive users. Within each of the two groups, serum and red cell folate concentrations did not vary significantly with the time of the menstrual cycle. In the group of pregnant women studied, both serum folate and red cell folate levels were found to increase over the course of pregnancy. However, the rise in serum folate was not statistically significant, and the increase in red cell folate was significant between the first and second trimesters (p<0.05) but not between the second and third trimester. It is not clear why the folate status of the pregnant subjects improved during the course of pregnancy. There was no difference in the levels of dietary folate intake among the three groups of subjects. The degree of correlation between the serum folate levels and dietary folate intake was consistently higher in the control women than in the women using oral contraceptives. The difference in correlation coefficients between the two groups was statistically significant (p<0.01) only at day 5 of the cycle. In the group of pregnant women the correlation between serum folate and dietary folate was higher in the first trimester than in the third trimester; but the difference in correlation coefficients was not statistically significant. There was no significant correlation between red cell folate levels and dietary folate intake in any of the three groups of subjects. These results indicate that oral contraceptive use reduces serum folate levels, and that this decline in serum folate is Independent of dietary folate intake. Thus, there appears to be some direct effect of synthetic sex hormones in reducing serum folate levels. Whether this is an effect at the level of intestinal absorption or tissue utilization remains unclear. If women using oral contraceptives are not able to fully absorb or utilize their dietary folate, it may be that their recommended daily allowance for folate should be increased.

Text

2010-01-28

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http://hdl.handle.net/2429/19302

Human Nutrition

University of British Columbia

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