MacFarlane AJ, Page R, Robichaud A, Arbuckle TE, Fraser WD. American Journal of Clinical Nutrition. 2017 May;105(5):1101-1109. doi: 10.3945/ajcn.116.137968
Breast milk is rich in many essential vitamins, including folates, which are needed for fetal and neonatal growth and development. In Canada, it is recommended that women who may become pregnant, are pregnant, or are breastfeeding should consume a multivitamin with 400 µg folic acid/day. Folic acid is the synthetic (man-made) form of folate and is broken down (metabolized) by the liver into folates. Some concerns have been raised that consuming too much folic acid may overwhelm the liver’s ability to metabolize folic acid into folates. Data are limited on the levels of total folate and unmetabolized folic acid in breast milk of Canadian women who consume folic acid from both folic acid-enriched foods (e.g., white flour) and vitamin supplements. The aims of this study were to determine the folate and unmetabolized folic acid content of breast milk and examine the relation with use of folic acid supplements.
Both total folate and unmetabolized folic acid were measured in samples of breast milk from MIREC Study participants and information on supplement use was obtained from the questionnaires that participants completed.
In this analysis of breast milk from 561 women (401 women reported taking supplements with folic acid and 160 did not take supplements) supplement users tended to be older (on average 33 years of age) and had a higher education and annual family income than those women who did not take supplements. Unmetabolized folic acid was detected in the breast milk of more than 95% of participants. Breast milk folate content was higher (18%) in those women who consumed folic acid supplements than those who did not. Women who consumed more than 400 µg folic acid/day had much higher (126%) levels of unmetabolized folic acid in their breast milk than those who did not report consuming supplements.
In conclusion, folic acid supplement use was associated with modestly higher folates in breastmilk. Unmetabolized folic acid was detected in almost all the breast milk analysed, including in women who did not consume a folic acid supplement. The results of this study suggest that consuming more than the recommended 400 µg/day of folic acid may exceed the body’s capacity to metabolize folic acid. Therefore, folic acid supplement doses greater than 400 µg/day may not be necessary, especially in populations such as those in Canada where food fortification with folic acid is mandatory.