DURHAM, N.C. -- Doctors have long warned Americans about the health hazards of high cholesterol, but a growing body of evidence indicates that very low cholesterol can be dangerous too, according to a researcher at Duke University Medical Center.
In a study of 121 healthy young women, Duke psychologist Edward Suarez found that those with low cholesterol levels -- below 160 mg/dl -- were more likely to score high on measures of depression and anxiety than women with normal or high cholesterol levels. Normal cholesterol levels are considered to fall within the range of 180 mg/dl to 200 mg/dl.
While the women in his study were not being treated for depression or anxiety, their scores on standard personality profiles clearly put them at risk for developing depression and anxiety, Suarez said.
Results of the study, funded by the National Heart, Lung and Blood Institute, are published in the May issue of the journal Psychosomatic Medicine.
"There is now a compelling body of evidence in both men and women that low cholesterol is a potential predictor for depression and anxiety in certain individuals," said Suarez, referring to his own and other studies showing the same effect in men. "While we certainly don't advocate that women indulge in high-fat foods, our data do suggest that women with naturally low cholesterol could benefit from raising their cholesterol through healthy dietary measures, like consuming more fish or fish oil."
Depression is the most common mental illness in America, affecting more than 17 million people at a cost of $30 billion to $44 billion per year to the nation's health care economy, Suarez said. Defining who is at risk and why could speed diagnosis and improve treatment for what is currently an under-treated disease, he said.
"Someday, screening for depression may encompass a cholesterol test, especially at significant points in a woman's lifetime when her cholesterol levels are known to drop," said Suarez. After childbirth, for example, a woman's cholesterol level drops precipitously, giving rise to the novel theory that some cases of postpartum depression result from low cholesterol, he said.
In addition, pinpointing low cholesterol as a risk factor for depression adds weight to the theory that depression and other mental disorders are largely determined by a person's biological makeup and not by his or her lifetime experiences alone, Suarez said.
Already, researchers have identified several biologic risk factors for depression, including a family history of the disease and certain neurologic changes in the elderly. And now, Suarez said there is evidence to suggest that having low cholesterol alters the way brain cells function. He said it is believed that brain cells with low levels of cholesterol have fewer serotonin receptors, preventing them from properly using this mood-stabilizing brain chemical.
"If we assume that amounts of cholesterol circulating in the blood reflect levels in the brain, then brain cells are not functioning properly in individuals with low cholesterol," he said.
Further, cholesterol's importance throughout the body is gaining more prominence as researchers link it to a variety of critical functions, such as how immune cells work, said Suarez.
Long involved in studying the effects of stress and depression in women, Suarez' interest in cholesterol and mood grew out of a series of large studies conducted years ago in men with high cholesterol. While men in the study were reducing their cholesterol levels through medications, their overall mortality rate was not declining. In fact, the rate of suicide and death from violent causes increased during the study, leading researchers to theorize that low cholesterol levels were causing mood disturbances.
Based on these findings, Suarez conducted several small pilot studies in women, adding a measurement of anxiety to the research, before conducting the current study in women aged 18-27. In the current study, women were asked to complete the NEO-Personality Inventory and Spielberger's Trait Personality Inventory, two detailed questionnaires that measure personality and mood characteristics.
Thirty-nine percent of the women with low cholesterol scored high or very high on personality traits indicating they are prone to depression, whereas just 19 percent of women with normal or high cholesterol scored high on these same measures, the study found.
Similarly, 35 percent of women with low cholesterol scored high or very high on a scale of anxiety, compared to just 21 percent of women with normal or high cholesterol.
All the women were healthy, non-smokers of normal height and weight. The majority exercised regularly, and none of the women was taking medications. In the future, Suarez plans to study the effects of low cholesterol in women who are clinically depressed and to assess the effects of low cholesterol on immune function.