Folic acid is also known as folate. Folic-acid deficiency causes birth defects and seems to contribute to heart disease and stroke.
The study looked at 728 Dutch men and women aged 50 to 70. Unlike the U.S., the Netherlands does not require folic acid supplementation of flour.
Participants in the Dutch study had high blood levels of homocysteine. Folic acid reduces homocysteine levels, so the Dutch study participants apparently consumed very little folic acid.
Half the study participants got strong folic acid supplements -- 800 micrograms per day, about twice what one would get in a multivitamin pill. The other participants got an inactive placebo pill.
After three years, those who got folic acid pills had less low-frequency hearing loss than did placebo recipients. The difference was slight: 0.7 decibels. The smallest change in sound intensity most people can notice is 1.0 decibels.
There was no slowing of high-frequency hearing loss. That may be because high-frequency hearing loss begins earlier in life than age 50.
Researchers Jane Durga, PhD, of Wageningen University, Netherlands, and colleagues suggest that by fortifying their flour with folic acid, nations might lessen their citizens' age-related hearing loss.
If a little folic acid from flour is good, would more folic acid be better? That's not known, suggests Robert A. Dobie, MD, of the University of California, Davis. Dobie's editorial accompanies the Durga study in the Jan. 2 issue of Annals of Internal Medicine.
"If this [hearing] benefit applies to the entire population (a big 'if') and continues to accrue each year (another big 'if'), one might expect a 5-decibel reduction in age-related [hearing loss] over a 20-year period," Dobie calculates.
Such a shift would cut the percentage of 75-year-old men who need hearing aids from 33% to 22%.
Dobie notes that much more study is needed to see whether the study results -- seen in people with low folic-acid intake -- might apply to the better-nourished U.S. population.