When people eat ferrocyanides, their bodies absorb only a tiny amount—less than half a percent—and it doesn’t build up inside them, so very little actually gets into the system.

What we've found so far suggests that humans absorb very little ferrocyanide when it is ingested orally. The evidence we’ve reviewed indicates that less than half a percent of ingested ferrocyanide is absorbed by the body [1]. Our analysis of the available research shows that when people consume ferrocyanides, the vast majority passes through the digestive system without entering the bloodstream [1]. Only a tiny fraction—less than 0.5%—is absorbed, and there is no indication from the evidence that it accumulates in the body over time [1]. This means that even if someone regularly consumes ferrocyanide, the amount that actually gets into their system remains extremely low. We base this on one clear assertion supported by two studies, with no studies found that contradict it [1]. Still, the total number of studies directly measuring human absorption is limited, and no long-term data on repeated exposure were included in our review. So while the current evidence leans toward very low absorption, we can’t yet say how this might vary across different forms of ferrocyanide, diets, or individual health conditions. Our current analysis does not rule out the possibility that absorption could change under certain circumstances—such as high doses or interactions with other foods or gut conditions—because the evidence doesn’t address those scenarios. Practical takeaway: Based on what we’ve reviewed so far, it appears that almost all of the ferrocyanide you eat passes through your body without being absorbed. The amount that does get in is extremely small.