A study at Johns Hopkins University’s School of public health has found a link between excessively high levels of folic acid in pregnant women and an increased risk of autism for the child. Folic acid is the supplement form of folate, the naturally occurring B vitamin that is crucial to the proper neurological development of fetuses. It had been previously known that deficiencies in folate in pregnant mothers caused birth defects and increased the risk of autism, this study is showing how it is just as dangerous in excess. 

The study took data from nearly 1,400 mothers giving birth between 1998 and 2013, measuring their blood folate levels within the first 3 weeks of delivery. Very high levels of folate doubled the risk of autism, researchers found. Increasing the risk were also high levels of B12, which tripled the risk of a child developing autism. If both B12 and folic acid levels were high, the risk is increased 17.6 times.

Officials part of the study want pregnant women to still take folic acid, but that further studies were needed to determine what the safe levels are. Moderate levels of both B12 and folic acid have a lower risk of developing autism.

The Center for Disease Control and Prevention however says that a quarter of reproductive-aged women in the US still don’t get enough folic acid.