Jefferson Researchers Develop Blood Test to Determine Hormone Levels Associated With Obesity

Researchers at Jefferson Medical College have created a blood test to determine the level of leptin in humans. Leptin is the hormone product of the obesity gene. Their findings, published in the January 31, 1996 New England Journal of Medicine, indicate that obese individuals have higher levels of leptin than persons who are lean. This research suggests that obese persons who have high levels of leptin may have a decreased sensitivity to leptin.

"We were able to make the association between leptin levels and obesity by using a newly developed blood test, which enabled us to track leptin in humans. This research is an important next step to narrowing down the mechanisms that lead to obesity," explained José F. Caro, MD, chairman of Jefferson's department of medicine and senior author of the study. "By the same token, this information is equally important to understanding why some people remain lean, while others develop obesity later in life."

In the article, the Jefferson investigators report that several factors may contribute to the elevation of leptin in obese individuals, but the values were most closely correlated with the percentage of body fat. They concluded that, at least in humans, leptin levels reflect the amount of fat tissue in the body.

According to Dr. Caro, the human obesity gene appears to be involved in the mechanism by which the increase in body fat translates into an increase in leptin. Researchers found a significantly greater amount of the obesity messenger protein in the fat cells of obese subjects than in normal-weight subjects.

Because this study concludes that many obese persons do have higher levels of leptin, it appears that human obesity is more likely caused by errors in the central mechanisms regulating food intake and energy expenditure. Animal studies previously had indicated that human obesity could be caused by a defect in the signals that are put forth by fat cells. However, this study reconfirms that, in humans, the signal is working properly, but that for reasons yet unknown, the brain is not adequately reading the signals.

Since leptin concentrations in the blood are related to body fat, this blood test may help predict who will become obese.

Additionally, for people who are overweight, but whose leptin levels are normal, treatment with additional leptin may become a therapy option, and may be available within three years, Dr. Caro explained. For obese persons whose leptin levels are high, researchers will need to pursue treatment options that will allow the "stop eating" message to be properly read by the brain.

"The blood test eventually will be available to the public," noted Dr. Caro. "But the relationship between leptin and obesity certainly needs further reference and study."