The studies, both published in the Proceedings of the National Academy of Sciences, examined the link between the neuroendocrine system and white blood cell function.

"These two studies, while not directly related, show that the neuroendocrine system plays a big role in both the immune system and obesity," lead scientist for both studies Pamela Fraker said in a statement.

The first study discovered leptin -- a hormone produced by fat cells that control how much food is eaten and how quickly energy is burned -- also supports white blood cell production, which in turn enhances immune function.

"This is a brand new role for leptin," Fraker said. "It appears that most obese people may be somewhat immunosuppressed. This finding shows us that the body's resistance to leptin plays a role in that, too."

The second study found corticosteroids produced naturally in the body do not suppress the immune system in the way prescription steroids -- such as inflammation-reducing prednisone -- do.

"With the pharmacological versions of steroids, you lose some immune function," Fraker said.