The B vitamin folate (B9) is found naturally in a variety of foods including vegetables (especially dark leafy greens), fruits and fruit juices, nuts, beans, peas, seafood, eggs, dairy products, meat, poultry, and whole grains. Folic acid is a synthetic, shelf-stable form of folate that is used in enriched or fortified foods and vitamin supplements. “Much of the folic acid we ingest in fortified foods or supplements is converted to a more natural form of folate in our gut, so the two forms historically were considered relatively equivalent,” says Joel Mason, MD, professor of nutrition and medicine and senior scientist and director of the Vitamins and Carcinogenesis Laboratory. “More recently, concerns have been raised that folic acid may not behave exactly the same as natural forms of folate in the body, and that consuming too much folic acid could potentially have some negative health effects.”
What We Need: In the U.S., the recommendation for folate intake is 400 micrograms (mcg) per day for people over the age of 14, except for pregnant or lactating women for whom the recommendation is 600 mcg per day. While most Americans get enough folate from the foods they eat, women of childbearing age are at risk of insufficient folate intake. This is of particular concern because low folate intake during the first month of pregnancy leads to a higher risk of neural tube defects—birth defects of the brain, spine, or spinal cord, such as spina bifida. To reduce this risk, U.S. manufacturers are required to add folic acid to enriched flours, breads, cereals, corn meals, pastas, rice, and other grain products. Since this mandatory fortification began in 1998, rates of neural tube defects in the U.S. have declined by 28 percent.
Potential Health Concerns: The main areas of concern being studied with regard to excessive folic acid intake are vitamin B12 deficiency and cancer. “B12 deficiency can cause neurological effects such as numbness and tingling in hands, legs, and feet; cognitive difficulties; and memory loss,” says Irwin Rosenberg, MD, professor emeritus and former dean of Tufts’ Friedman School of Nutrition Science and Policy. “In the presence of low B12 levels, high folic acid intake may mask or worsen these neurologic effects. High folic acid in combination with low B12 has also been associated in some studies with lower cognitive function among the elderly.” People at increased risk for B12 deficiency include older adults, individuals who avoid animal products in their diets, such as vegetarians and vegans, and people on long-term acid suppressing medications for reflux.
“There is also some concern that excessive folic acid intake may increase the risk for some types of cancers,” says Mason. The relationship of folate to cancer is complex. “There are compelling data that people who habitually get too little folate from foods are at increased risk for colorectal cancer,” says Mason. “However, animal studies, as well as a few observation studies in people, suggest that this increased risk occurs for people who get too much as well, but this has yet to be proven conclusively.” Folate is needed for creating new copies of DNA. “It’s like a fertilizer for cell growth,” says Mason, “so at high levels it could, theoretically, encourage pre-cancerous cells to become cancerous. We have observational data suggesting this and several other health concerns exist, but we have yet to prove that there is any true cause and effect relationship in humans.”
“There is virtually zero evidence that we can get too much natural folate from the foods we eat,” says Rosenberg. “But emerging evidence suggests that exposure to too much folic acid may be potentially harmful, especially for some vulnerable groups.” Mason and Rosenberg are currently taking part in a National Institutes of Health initiative to lay out a research path to answer questions about the possible health effects of folic acid overload.