The rates of three rare childhood cancers have dropped since the U.S. began to fortify some foods with folic acid, a new study says.


The rate of Wilms' tumors, which develop in the kidneys, dropped from 18.4 yearly cases per 1 million children to 14.8 yearly cases per 1 million children, the study showed, after folic acid fortification of grain foods began in 1996.


The rate of tumors called primitive neuroectodermal tumors (PNETs) dropped from 4.2 yearly cases per 1 million children to 2.3 yearly cases per 1 million children. There was also a slight drop in the rate of tumors called ependymomas; both PNETs and ependymomas usually develop in the brain or spinal column.


All three cancers are believed to typically begin while a fetus is developing in utero, according to the study.


"Folate is critical for embryonic development," the researchers wrote in their study. Studies have shown that babies born to women who get enough folic acid during pregnancy have reduced risks of neural tube defects and some congenital abnormalities. After folic acid fortification began in foods, the rate of neural tube defects dropped by 31 percent, the study said.


Some previous evidence had also suggested a link between folic acid and a lower rate of childhood cancers.


In the new study, researchers at the University of Minnesota and Washington University in St. Louis used data from the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) program. They looked at cancer rates in children under age 5 between 1986 and 2008, but excluded children born between 1996 and 1998, because the fortification mandate was being implemented during the years these children were in utero.


In all, there were 3,790 cancer cases in children during the years before fortification, and 3,299 cases after fortification.


The researchers found that the drops in the rates of the rare tumors was greatest for children under age 1, though there was no drop in the overall rate of childhood cancers, they noted.


The study showed an association, not a cause-and-effect link between folic acid fortification and the drops in the cancer rates, the researchers noted. It's possible that the cancer rate reductions are due to other factors. However, there are reasons to think that folic acid did lower the cancer rate; for example, the sharpest decline was seen immediately following the beginning of fortification, they said.


Adults should consume 400 micrograms of folate daily, according to the 2010 U.S. Department of Agriculture dietary guidelines. A typical multivitamin contains 400 micrograms of folic acid, and a typical slice of enriched whole wheat bread contains 16 micrograms.


Folic acid is also called vitamin B9.


The study is published online on May 21 in the journal Pediatrics. The research was funded by the National Institutes of Health.


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