Researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University have shown that excess levels of folic acid causes lowered immune function through less effective natural killer (NK) cells in aged mice.
Their work was published this month in the Journal of Nutritional Biochemistry and built upon previous work by the same lab in 2005 that showed 78% of healthy postmenopausal women had excess folic acid intake due to unmetabolized folic acid in their blood plasma.
By supplementing the diets of mice with folic acid, at the equivalent of the recommended daily allowance (RDA) for humans in a control group and a 20 times intake for the treatment group, they reproduced the previous finding of an association in postmenopausal women between their excess folic acid intake and a lowered NK cell activity.
"If we want to optimize the efforts of NK cells to increase resistance to infections, the use of folic acid in some contexts may need to be reassessed. Among older adults, additional research might show that it is important to take supplements only if one has been documented to be folate-deficient," said Ligi Paul, who is the last author in the study.
According to the NIH's Office of Dietary Supplements, approximately 35% of people in the U.S. consume dietary folic acid. While dietary folic acid is without doubt recommended in pregnancy where risks of neural tube defects in newborns can be prevented, this new finding may spur a rethink for dietary requirements in older women and postmenopausal women.