High folate intake linked with nerve-damage risk in older adults

High folate (vitamin B9) consumption is associated with an increased risk for a nerve-damage disorder in older adults who have a common genetic variant linked to reduced cellular vitamin B12 availability.

It is important to consume the daily recommended level of vitamins and minerals for the proper functioning of the body. But consumption of nutrients more than the recommended levels may be harmful.

Excessive intake of folate is linked to nerve damage risk in older adults with a common genetic variant, according to a new study.

Folate is a water-soluble B vitamin that is naturally found in foods. It is an essential nutrient especially for infants, children and pregnant women (to prevent birth defects). Folate is the term for both naturally occurring in food and the synthetic form called as folic acid, which is found in fortified foods and supplements.

Although variable by race or ethnic background, an estimated one in six people in the U.S. carry two copies of a genetic variation inTCN2, a gene that codes for a vitamin B12 transport protein. For some of these individuals, theTCN2 variation (referred to as GG) can lead to conditions related to vitamin B12 deficiency even if they consume normal amounts of B12.

In an epidemiological study involving 171 adults aged 60 and older, a team led by scientists from the Jean Mayer USDA Human Nutrition Research Center on Aging at Tuft, found that individuals with the GG variant of TCN2 were three times more likely to have peripheral neuropathy, nerve damage commonly associated with vitamin B12 deficiency, when compared to individuals without the variant.

Ligi Paul, Ph.D., scientist in the Vitamin Metabolism Laboratory at the USDA HNRCA, and senior author of the study, said, "Due to the prevalence of the TCN2 variant, and because the average daily folate intake for US adults over 50 is already more than twice the RDA, we believe that our findings highlight a potential concern for a large proportion of older Americans."

"Our data suggest that older adults should keep folate intake close to the recommended amounts, and try to get nutrients from a balanced diet rather than depending on supplements," said Paul.

Older individuals are at particular risk for vitamin B12 deficiency due to decreased stomach acid production and use of certain medications, which interfere with the absorption of the vitamin from food. Long-term B12 deficiency can cause a range of symptoms, including anemia and peripheral neuropathy; damage to the peripheral nervous system marked by lack of coordination, weakness, or pain, tingling, and numbness in the hands and feet.

"Folate is a necessary vitamin and no one should think that it needs to be avoided. But in certain situations, very high intake of folate may be harmful," said lead author Hathairat Sawaengsri, Ph.D., who conducted the study while a doctoral student in the biochemical and molecular nutrition program at the Friedman School of Nutrition Science and Policy at Tufts University and a member of the Vitamin Metabolism Laboratory at the USDA HNRCA. "Vitamins and minerals should be consumed at an optimal level, not too high and not too low."

According to the National Institute of Health's Office of Dietary Supplements, approximately 35 percent of people in the U.S. consume folic acid in dietary supplements. Some population groups, particularly adults aged 50 and older, are at risk of consuming excess folate. The federal government's Dietary Guidelines for Americans advises that nutrients are best obtained from natural food sources.

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