Oats are often touted for lowering bad cholesterol,  improving the immune system, lowering blood pressure and, more recently, being gluten-free, but a new study finds that some oat-based breakfast cereals in the U.S. contain a mold-related toxin called ochratoxin A (OTA) that's been linked to kidney cancer in animal studies. 

Natural or not, they may need closer monitoring for potential mold contamination, warns a paper in the Journal of Agricultural and Food Chemistry. 

Dojin Ryu and Hyun Jung Lee note that ochratoxin A is one of the most common toxic products released by molds in the world. Previous studies have found the toxin in samples of pork, dried fruits, wine, coffee and other products. Scientists don't yet know how the toxin affects human health, but the International Agency for Research on Cancer, which is part of the World Health Organization, classifies it as a possible human carcinogen.

Animals exposed to ochratoxin A  in experiments developed kidney tumors and although the U.S. doesn't currently regulate the contaminant, the European Union has set maximum limits for ochratoxin A in food. Ryu and Lee wanted to see how U.S. breakfast cereals -- a staple in many Americans' diets -- measured up to that standard. 

The researchers tested close to 500 samples of corn-, rice-, wheat- and oat-based breakfast cereals purchased from U.S. stores over two years. They found that in most samples, OTA levels were lower than the European threshold. But concentrations exceeded the EU standard in 8 percent of oat-based breakfast cereal samples.

The researchers conclude that oat production, storage and processing need careful review to better protect consumer health.

Funded by the U.S. Department of Agriculture National Institute of Food and Agriculture.