September 22, 2000
(Center for the Advancement of Health) - Lean women who are vulnerable to the effects of stress may be more likely to accumulate excess abdominal fat -- increasing their risk for certain diseases, the results of a preliminary study indicate. "Our findings support the idea that greater life stress and stress reactivity can contribute to central fat, especially among lean women," said lead author Elissa Epel, PhD, who conducted the study while working as a research scientist at Yale University and is now with the University of California at San Francisco's Health Psychology Program.
According to the researchers, it is well established that people with diseases that cause extreme exposure to the stress hormone cortisol -- such as Cushingís Syndrome -- have excessive amounts of central or visceral fat. This type of fat is unhealthy, as it is linked to greater heart disease and diabetes. Epel and colleagues investigated whether the relationship between cortisol and central fat is found among healthy people as well.
Central fat tends to be highly sensitive to the effects of circulating stress hormones like cortisol. This type of fat responds to cortisolís presence by increasing in size -- thus heightening the risk of diseases such as high blood pressure, heart disease, stroke, and diabetes.
Although everyone is exposed to stress, according to the researchers, some people may secrete more stress-induced cortisol than others. Further, some people may secrete cortisol every time they face the same difficult situation, rather than adapting to it. Epel and colleagues predicted that people who react to the same stressor each day by secreting cortisol would have greater central fat.
The researchers noted study limitations, such as the homogeneity of the study participant group. "We do not know whether the current results would generalize to other ethnicities," said Epel. "We also donít know whether stress actually caused the central fat accumulation or whether they are parallel phenomena. Only longitudinal studies can determine this."
The researchers gave 59 white women laboratory stress tests over several days to examine cortisol responses over time. Approximately half of the women had a high waist-to-hip ratio (WHR), and the other half had a low WHR. A high WHR indicates fat storage at the waist, and a low WHR indicates fat storage at the hips more than the waist.
Women with a high WHR, both those who were overweight and those who were lean, appeared more vulnerable to stress: they were more threatened by the laboratory stress tests, made less effort on them over time, performed more poorly on them, and secreted more cortisol than women with a low WHR, the researchers found. In addition, the higher WHR women reported more stress from their daily lives.
As the study progressed, Epel and colleagues noted a difference among members of the high WHR group. Those who were overweight appeared to adapt to the laboratory stresses (puzzles and speech tasks that were similar in nature). Lean women with a high WHR, however, did not adapt. On the second and third days of the study they continued to secrete significantly more cortisol than lean women with a low WHR did.
The researchers report their findings in the September/October issue of the journal Psychosomatic Medicine.
The high WHRs of lean and obese individuals may have different causes, suggested Epel. The lean high WHR womenís psychological profiles revealed the most vulnerability to stress. This may have led them to overreact to stress in their daily lives. Greater cortisol exposure, in turn, may have caused them to accumulate greater abdominal fat. "For lean women, central fat may indicate an underlying sensitivity to stress rather than being in part a result of obesity," she said. "However, genetics also play a role in shaping both stress response and fat distribution."
"In addition, future research needs to better define levels of risk and appropriate treatments based not only on oneís girth but also on the multiple causes of central fat, such as genetics, behavior, general obesity, and chronic stress," said Epel.
"Many factors besides cortisol influence central fat, such as sex hormones and lifestyle factors. Smoking, alcohol, and lack of exercise increase it, whereas sufficient sleep and exercise may decrease cortisol levels and central fat," said Epel.