By: Christina Dell'Amore
For the first time, researchers have found that lower amounts of a mood regulating chemical in the brain is associated with early signs of heart disease, the No. 1 killer of men and women in the United States.
In research led by the University of Pittsburgh, people who had low levels of serotonin, a neurotransmitter and a regulator of mood, appetite, and blood pressure, were more likely to develop early heart disease. The researchers focused on a person’s level of atherosclerosis, of hardening of the arteries, which is the underlying process leading to heart disease.
"We haven’t thought about the brain as central to a cause of heart disease. Now we might have to think more alone those lines," said lead investigator Matthew Muldoon, an associate professor of medicine at the University of Pittsburgh.
Muldoon will present his research Friday at the Annual Conference of the American Psychosomatic Society in Denver. Muldoon and colleagues recruited 244 healthy volunteers between 30 and 55, all of whom showed no signs of heart disease. The researchers used ultrasonography imaging to measure the degree of thickening of the carotid artery, a major artery in the neck.
To determine how much serotonin was in the brain, Muldoon injected the volunteers with a common anti-depressant drug, which spurs the pituitary gland to release more prolactin, a type of hormone. Since prolactin reflects the strength of serotonin in the brain, the researchers then analyzed how much prolactin entered the blood stream. Volunteers with more thickening of the arteries had the lowest prolactin response.
This connection adds weight to a theory called "correlated risk," that may risk factors for heart disease may fan out from one, singular trigger in the brain, said one co-investigator Stephen Manuck, a professor of health psychology and behavioral medicine at the University of Pittsburgh.
"Serotonin may be one of the key elements in coordinating major factors that lead to early heart disease," Manuck said. Muldoon thought brain serotonin might be a prime candidate for testing the theory, since brain serotonin has been previously related to clustering of risk factors for other diseases. For instance, people with metabolic syndrome have a grouping of tendencies toward overweight, bad cholesterol, and diabetes. Testing serotonin and atherosclerosis’ was a next step in moving the idea along, Muldoon said.
The causes of heart disease are plentiful. Some are biological, such as diabetes and high blood pressure; some are psycho-social, such as depression or behavioral problems; and others relate to lifestyle choices, such as smoking. In large studies people who have one of these risk factors are likely to experience others.
People have low serotonin for several reasons, Manuck said. Those affected by crime and poverty may emit less serotonin, as do people who smoke. There’s also evidence genes play a role: some people have variants in their genes that changes serotonin levels in the brain.
Moreover, low serotonin is a symptom of depression, a disease growing by leaps and bounds in the United States. Manuck pointed out that depression is a risk factor for heart disease, and "it may tie together in the current package." A body of evidence also suggests people battling depression are more likely to die of cardiac diseases, and so Muldoons research could mean there is something different about the basic biology of depressed people, said Bruce G. Pollock, a neuropsychiatry professor at University of Toronto and a contributor to the paper.
It could show "something in their head" is contributing to their development of metabolic syndrome, which leads to heart disease, Pollock said. "It’s not as simple as saying depressed people just aren’t exercising or eating properly. This contributes to understanding their biology," he said.
So could this inspire a new strategy for treating heart disease? Not quite yet, Muldoon says, although “we may be on the road to a better understanding” of how to tackle it, he said.
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