Non-overweight women who are vulnerable to the effects of stress are more likely to have excess abdominal fat, and have higher levels of the stress hormone cortisol, a study conducted at Yale suggests.
While past studies have examined cortisol response in overweight women, this is the first study to show that lean women with abdominal fat have exaggerated responses to cortisol. Abdominal fat is related to worse health, including greater risk of heart disease and diabetes.
"We also found that women with greater abdominal fat had more negative moods and higher levels of life stress," said Elissa S. Epel, Ph.D., lead investigator on the study she conducted while at Yale's psychology department. "Greater exposure to life stress or psychological vulnerability to stress may explain their enhanced cortisol reactivity. In turn, their cortisol exposure may have led them to accumulate greater abdominal fat."
Published in the September/October issue of Psychosomatic Medicine, the study looked at pre-menopausal, non-overweight women, and overweight women who stored fat either centrally--at the waist vs. peripherally--at the hips, and examined their stress responses over three consecutive days.
Cortisol affects fat distribution by causing fat to be stored centrally--around the organs. Cortisol exposure can increase visceral fat--the fat surrounding the organs--in animals. People with diseases associated with extreme exposure to cortisol, such as severe recurrent depression and Cushing's disease also have excessive amounts of visceral fat.
"Everyone is exposed to stress, but some people may secrete more cortisol than others, and may secrete cortisol each time they face the same stressor," Epel adds. "We predicted that reacting to the same stressors consistently by secreting cortisol would be related to greater visceral fat."
After the first exposure to stress, women with greater abdominal fat felt more threatened by the study's stressful tasks, performed more poorly on them, and secreted more cortisol. They also reported more life stress. By the third exposure to stress, the lean women with abdominal fat still consistently secreted more cortisol in response to stressful lab tasks, compared to women with peripheral fat.
"It is possible that greater exposure to stressful conditions or psychological vulnerability to stress has led them to overreact to stressors in their daily lives, so they have had greater lifetime exposure to cortisol," Epel said. "Cortisol, in turn may have caused them to accumulate abdominal fat. Genetics, however, also play a role in shaping reactivity to stress, as well as body shape."
Lifestyle and age may also influence levels of abdominal fat. Smoking, alcohol and lack of exercise all contribute to greater abdominal fat. Postmenopausal women tend to carry fat at their abdomen, due to changes in sex hormones. Epel said a healthy lifestyle, including getting enough sleep, exercise and relaxation, may reduce cortisol levels.
"These relationships likely apply to men as well," Epel said. "However, excess weight on men is almost always stored at the abdomen. On the contrary, in pre-menopausal women, excess weight is more often stored at the hips. Therefore, for women, it is possible that stress may influence body shape more than for men, leading to abdominal fat instead of lower body fat accumulation."
Elissa Epel's research team at Yale included Kelly D. Brownell, Ph.D., Jeannette R. Ickovics, Ph.D., Jennifer Bell, and Grace Castellazzo. Other researchers included Bruce McEwen, Ph.D. of the Rockefeller University; Teresa Seeman, Ph.D., of the University of California, Los Angeles; and Karen Mathews, Ph.D. of the University of Pittsburgh.
The study was funded by the MaCarthur Foundation Research Network on Socioeconomic Status and Health.
Elissa Epel can be reached at the University of California, San Francisco's Health Psychology Program. (415) 885-7277.