Docosahexaenoic acid (DHA, C22:6 (n-3)) is a long chain fatty acid required for eicosanoid synthesis, and in this capacity can inhibit inflammation and platelet aggregation. In addition DHA is preferentially incorporated into the brain tissue, where it may function to improve cognitive function. Pregnant women have a high requirement for DHA because the growing foetus has a large capacity to store DHA, and following parturition, the growing infant is dependent on its mother for its DHA requirement. Phosphatidylcholine is a phospholipid that is incorporated into cell membranes, and comprises of two fatty acids attached to a glycerophosphocholine backbone. Phosphatidylcholine synthesised via the S-adenosylmethionine dependent phosphatidylethanolamine N-methyltransferase pathway (PEMT) is enriched with DHA, such that it is more likely to contain DHA as one or both of its fatty acids. However, phosphatidylcholine can also be produced by the cytidine diphosphate choline (CDC) pathway which does not enrich phosphatidylcholine with DHA.
Dietary choline can serve as a methyl donor in the PEMT pathway and this may therefore increase the production of DHA enriched plasma membranes by increasing flux through PEMT but not the CDC pathways. Supplementation of DHA has been shown to increase plasma and erythrocyte concentrations of DHA. Therefore supplementation of choline and DHA together may have a potentially synergistic effect. In one study1 the plasma and erythrocyte phosphatidylcholine-DHA concentrations of women were measured following administration of 480 or 930 mg per day of dietary choline for 12 weeks together with a 200 mg per day DHA supplement. In pregnant women, no significant differences in plasma-DHA or erythrocyte-DHA were evident. However, The erythrocyte phosphatidylcholine-DHA concentrations increased significantly at the 930 mg per day dose in nonpregnant women when compared to the 480 mg per day dose. In addition, the nonpregnant women had a faster increase in plasma phosphatidylcholine-DHA at the 930 mg per day dose compared to the 480 mg per day dose.
These results show that choline can influence the phosphatidylcholine-DHA concentration of nonpregnant healthy women. This may be because choline can stimulate flux through the PEMT pathway and increase the amount of DHA incorporated into phosphatidylcholine. However, these effects are not evident in pregnant women. This reason for this discrepancy might be that the flux through the PEMT pathway is already elevated in pregnant women. Evidence for this comes from a higher phosphatidylcholine-DHA concentration in the pregnant women when compared to the nonpregnant women. The need for DHA by the growing foetus as structural components of the brain may therefore cause an increase in the PEMT pathways in order to fulfil this requirement. As nonpregnant women do not have this requirement dietary choline supplements may have an effect because of the lower activation of this pathway. The contention that choline is beneficial to the brain and memory may therefore stem partly from its ability to increase plasma and erythrocyte phosphatidylcholine-DHA concentrations.
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