Doctors have long been puzzled as to why healthy toddlers can sometimes suddenly have a stroke. Now, researchers at the Hospital for Sick Children in Toronto have found that these children are 10 times more likely to have iron-deficiency anemia than other kids in this age group.

Although childhood stroke is rare, it occurs in three children in Canada per 100,000 annually and can lead to brain damage and, occasionally, death.

The study, which included researchers from the University of Toronto found that children with iron-deficiency anemia accounted for more than half of all stroke cases in children without an underlying medical illness.

That, they say, is an indication that iron-deficiency anemia is a significant risk factor for stroke in otherwise healthy toddlers.

Iron-deficiency anemia is caused by a lack of iron in a child's diet and is considered relatively common -- especially among toddlers who consume large amounts of cow's milk, a food product that does not contain iron and can inhibit its absorption in other foods.

Iron-deficiency anemia diminishes the blood's ability to carry oxygen from the lungs to the rest of the body. It has long been seen as a condition that could lead to cognitive and motor developmental delay, but was not considered life-threatening. Now, this new study suggests it could be just that.

The study looked at 56 children between one and three years of age who were admitted to hospital between 1992 and 2004 with stroke. Fifteen of these children who were previously healthy and had no identifiable risk factors for stroke were considered as case patients. A control group of 143 healthy children in the same age range were also recruited for the study.

Researchers found that iron-deficiency anemia was significantly more common among the stroke patients (53 per cent) than the control subjects (nine per cent). That is almost a six-fold difference.

The research is reported in the November issue of the journal Pediatrics.

Dr. Jonathon Maguire, the study's lead author, says the cause of the association between iron-deficiency anemia and childhood stroke is still unknown. But he says his team found that children with stroke were five times more likely to have a high platelet count compared to children who did not have a stroke, suggesting that may be a factor.

Platelets are small fragments of cells that stick together to stop bleeding after a cut or injury. Too many platelets can cause blood clots to form, which can lead to stroke.

Researchers were not able to determine the proportion of young children who have iron-deficiency anemia and who may therefore be at risk of stroke.

Dr. Patricia Parkin, the study's lead investigator and associate scientist at Sick Kids says this study shows that there needs to be greater attention given to early detection of iron-deficiency anemia in young children.

"Strategies need to be developed to prevent iron-deficiency anemia from occurring and to detect it early so that it can be treated before a life-altering complication like a stroke develops."

Parkin adds that parents and caregivers can help prevent iron deficiency by ensuring that a variety of iron-rich foods are included in their child's diet.

Meat, fish, egg yolks, beans, and whole-grain bread are good sources of iron.