The study by researchers at Wake Forest University School of Medicine appears as the cover story of the current issue of Obesity, the peer-reviewed journal of the Obesity Society.
Carol A. Shively, Ph.D., a professor of pathology and the study's principal investigator, said: "We are in the midst of an obesity epidemic.
"Much of the excess fat in many people who are overweight is located in the abdomen, and that fat behaves differently than fat in other locations. If there's too much, it can have far more harmful effects on health than fat located in other areas."
She notes that obesity is directly related to lower socioeconomic status in Western societies, as is heart disease. So, the people who have fewer resources to buffer themselves from the stresses of life are more likely to experience such health problems, she said.
In this study of how the stress of low social status affects the development of heart disease, female monkeys were fed a Western-style diet containing fat and cholesterol. The monkeys were housed in groups so they would naturally establish a pecking order from dominant to subordinate. Subordinate monkeys are often the target of aggression and aren't included in group grooming sessions as often as dominant monkeys.
Shively and colleagues Thomas C. Register, Ph.D., and Thomas B. Clarkson, D.V.M., all faculty of the Department of Pathology, Section on Comparative Medicine at the School of Medicine, found that these socially stressed subordinate monkeys developed more fat in the viscera, or abdominal cavity.
The researchers found that the stress of social subordination results in the release of stress hormones that promote the deposition of fat in the viscera.
In turn, visceral fat promotes coronary artery atherosclerosis, the buildup of plaque in the blood vessels that leads to heart disease, the leading cause of death in the world today.
What is striking about that relationship, Shively said, is that women and female monkeys have a natural protection against heart disease - women typically develop heart disease, on average, 10 years later than men do. That protection seems to be lost when stress and visceral fat increase.
Researchers found that the monkeys with high social stress and larger amounts of visceral fat also had ovaries that produced fewer protective hormones.