People with heart disease often experience horrific sleep problems, and now, scientists have identified a direct link between these conditions for the first time in a new study of mice and human tissue.
The study, published in the journal “Science”, showed that heart disease may impede the production of the sleep hormone melatonin in the brain due to damage to a group of nerves that connect to both organs, the “superior cervical ganglion” (SCG), reports Al-Rai daily quoting Reuters.
These nerves are found in the neck and are part of the autonomic nervous system that regulates involuntary processes in the body, such as breathing and heart rate.
Since nerves that originate from the superior cervical ganglion connect to both the heart and the pineal gland, the delicate brain structure responsible for producing melatonin, heart-related issues could explain why the body’s melatonin maker goes off track.
“Imagine the node as an electrical switch box,” study senior author Stefan Engelhardt, a professor of pharmacology and toxicology at the Technical University of Munich, said in a statement. In the case of a patient who suffers from sleep disturbances following a heart condition, you can think of a problem with one of the wires causing a fire to start in the switch box and then spread to another wire.”
The research is “important and timely,” Brooke Aggarwal, an assistant professor of medical sciences at Columbia University who was not involved in the study, told Live Science, noting that it “suggests a new mechanism that may help explain why people with heart disease are more prone to sleep disturbances.”
“Future studies should be conducted, in addition to clinical trials, of any potential therapies arising from this mechanism,” Aggarwal added in her warning.
Struggling to sleep is a common side effect of heart disease, for example, as many as 73 percent of people with heart failure experience symptoms of insomnia. Previous studies have shown that melatonin levels drop in people with heart disease, but scientists don’t know why.
In the new study, the researchers analyzed samples of human brain tissue taken from deceased heart patients and from people without heart disease.
This post-mortem analysis revealed a lower number of nerve fibers, or axons, in the superior cervical ganglion of people with heart disease compared to a healthy heart control group.
The superior cervical node of the subjects with heart disease was significantly enlarged.
In mouse experiments, the team found that immune cells called macrophages, which devour diseased and damaged cells, were present in the cervical ganglion of mice with heart disease, and the rodents’ nerves showed signs of inflammation and scarring. The mice also had fewer axons in their pineal glands and less melatonin in their blood than healthy mice. The rodents’ circadian rhythms (the internal processes that regulate how the body responds to day and night) were also disrupted, as evidenced by changes in metabolic rates and activity levels, for example.
The team found that giving melatonin to mice completely reversed this disorder. In addition, when the drugs were used to destroy macrophages in the rodents’ superior cervical ganglion, their melatonin levels were restored.
Because these analyzes were performed on mice and only 16 people, the results require further studies to uncover the mechanisms that drive immune cells to the upper cervical ganglion, the researchers note in the paper. This may involve studying neurons that connect the heart and spinal cord, as well as messenger proteins called cytokines that call on macrophages.
The team believes the study could pave the way for the development of new drugs to treat sleep disorders caused by heart disease.
“It will now be important to have evidence in a randomized clinical trial to determine whether therapeutic melatonin is actually effective in treating sleep disorders in patients with chronic heart disease,” Engelhardt said. If proven effective, this could spare many patients the unnecessary side effects that come with regular sleeping pills.”
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