ANN ARBOR, Mich., April 2 (UPI) -- High levels of a hormone called leptin, which is produced by fat cells, could increase the risk for potentially lethal blood clots, according to a new study released Tuesday.
Researchers at the University of Michigan Medical School in Ann Arbor said obese people have a tendency to develop dangerous blood clots, but the relationship between obesity and clotting risk is not well understood.
To find the reason, scientists led by Dr. Daniel T. Eitzman, a cardiologist and assistant professor of internal medicine, studied varying leptin levels in mice.
Eitzman looked at a group of overweight mice that were genetically engineered to lack the gene needed to produce leptin. He found they took an average of 75.2 minutes to clot, almost twice as long as normal mice who clotted at 42.2 minutes.
Blood clotting capabilities were tested on another group of mice missing the gene for the leptin receptor, which also made them leptin deficient. Like the first group of mice, the second group also took a long time to clot, about 68.6 minutes.
When they injected leptin into the mice, however, clotting times dropped to normal, around 41.8 minutes. "Fat mice, they clot quicker," Eitzman told United Press International.
The findings are published in the April 3 issue of Journal of the American Medical Association.
Leptin is released by fat cells and signals the body to stop eating. But this system can break down in overweight people, Eitzman explained. Leptin levels can get too high among obese individuals and when that happens, the person can become resistant to leptin's signals, making them more vulnerable to the hormone's effect on blood-clotting.
"For some unclear reason, in terms of the appetite suppression, they don't respond as one would suspect to elevated forms of leptin," Eitzman said. "There's probably some molecular basis to this."
Eitzman added, "It's becoming very clear the fat tissue is a very functional, active organ and it produces substances that could affect cardiovascular disease in a negative way."
Although the molecular interaction needs to be explored, Eitzman said one tried and true way to lower potentially harmful leptin levels is to lose the fat that produces it.
"If you lose weight and you lose fat, your leptin levels go down," he said.
"I don't know the leptin levels, per se, predict risk," Dr. Philip Comp, professor of medicine at the University of Oklahoma in Oklahoma City, told UPI. "Those are hard studies to do. It's a long way from mouse to man ... because there are so many other things that are going to influence who's going to get the clots."
Some people may be overweight, but physically fit, Comp explained. And some folks might be obese, but have strong genetics. It just varies so much from person to person, he said.
"Just one risk factor isn't enough," he said. "When it gets down to humans, it gets very hard to tease out the effects."
(Reported by Katrina Woznicki in Washington)
