It's a new clue in the efforts to determine the true causes of childhood blood cancers.
Three-year-old Ruben Stoiloff's smile is perfectly straight now, but two years ago he scared his mom when his face looked crooked.
"Just one morning, he woke up and the right side of his face was paralyzed," said Ruben's mom Lily Stoiloff.
She was stunned when she heard the diagnosis: leukemia.
"I was shocked. I thought the worst. I thought I was going to lose my son," she said.
All through treatment, Lily Stoiloff kept asking herself what could've caused such a devastating disease.
"We looked into a lot of things, we went on the Internet. The doctors didn't really give us a cause," she said.
Experts don't know for sure what causes leukemia, the answer could be part genetics and environment. But Dr. Steven Mittelman and his colleagues at Childrens Hospital Los Angeles are following a promising clue.
Both leukemia and obesity have been steadily on the rise for the past two decades and Dr. Mittelman says his study on mice confirms a connection.
"This was the first study to show that obesity itself actually accelerates leukemia progression," Dr. Mittelman said.
Dr. Mittelman is looking at the secretion of various hormones that occur during obesity.
"Some of the evidence itself implies that it's actually the weight itself and not necessarily the diet," he said.
Not only can obesity increase a child's risk of getting leukemia, previous research done at Childrens Hospital L.A. reveals obesity could make treating certain blood cancers more difficult.
"If the leukemia cells are hidden in fat and the chemotherapy can't effectively treat them there then that could be a reason for resistance," said Dr. Mettelman.
The next step Dr. Mittelman says is to figure out the exact relationship between fat and leukemia cells.
But experts agree the findings just add to the long list of reasons to encourage a fit and healthy lifestyle in children.
Researchers at Childrens Hospital L.A. say leukemia is the most common type of childhood cancer, so understanding how obesity may increase its incidence could have important public health implications.
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