Scores of scientific studies have sought to discover the causes of obesity in humans. But while investigating a certain hormone known to influence appetite, researchers at the School of Medicine have discovered that the hormone has a profound influence on cognitive ability as well as eating habits.

The hormone, ghrelin, was first discovered by Japanese researchers in 1999, and has been recognized for several years as being somehow related to appetite and body weight. Ghrelin levels increase before meals and decrease after eating. Speculation has abounded as to the hormone’s potential usefulness in preventing obesity, but Yale’s researchers, working in cooperation with researchers at Washington University in St. Louis and the University of Cincinnati, seem to have uncovered a previously unknown effect.

“The discovery was a byproduct of our research into how ghrelin regulates food intake,” said the project’s leader, Dr. Tamas Horvath, chair of comparative medicine at the Medical School. “By looking at how ghrelin binds to parts of the brain that regulate food intake, we found that it also binds to other parts, such as cortex and hippocampus.”

Horvath said these discoveries are applicable in a non-medical context, as well.

“A practical recommendation could be that children may benefit from not overeating at breakfast in order to make the most out of their morning hours at school,” he said.

Ghrelin’s influence on these areas of the brain could be immediately relevant not just to everyday cognition, but also to pathologies that affect mental capacity.

“In Alzheimer’s, the hippocampus is the area that shows the most atrophy,” said Dr. Ewan McNay, an endocrinology researcher on the team. “The research we’re doing will lead to a better understanding of what goes wrong in Alzheimer’s and other old-age diseases so they can be better treated.”

The conditions affected by ghrelin may be part of a series of other medical issues which can be controlled, or perhaps cured, by investigating this hormone, researchers said.

“It has also been shown that Alzheimer’s disease is linked to obesity and insulin resistance and that obesity increases the progression of dementia, like in Alzheimer’s disease,” said neurobiology and obstetrics and gynecology professor Sabrina Diano, who also worked on the ghrelin project. “In addition, it is important to study whether ghrelin could affect other types of pathologies that involved the hippocampus, such as epilepsy.”

The project’s members agree that the next logical step for researchers will be to investigate whether ghrelin’s effects on humans are consistent with its effects on laboratory rats. If so, work could begin on adapting current knowledge of ghrelin into medical practice.

“The general take-home message is that the supply of fuel to the neurons, as well as the mechanisms involved in controlling the supply, is critical for both optimal normal function and for the loss of function as seen in Alzheimer’s, aging and so on,” McNay said.