CHICAGO - Depression, severe mental illness and loneliness are linked to illnesses such as heart disease and dementia, according to several studies published on Monday.

A man walks in heavy fog on a beach in a file photo. Depression, severe mental illness and loneliness are linked to illnesses such as heart disease and dementia, according to several studies published on Monday. [Reuters]

The exact connections between a dysfunctional mind and a malfunctioning body remains an ongoing question, but at least one of three sets of researchers writing in the Archives of General Psychiatry said several factors may be at work.

Dr. Jesse Stewart, formerly of the University of Pittsburgh School of Medicine, found a correlation between depression and hardening of the arteries in his three-year study of 324 men and women who averaged 60 years old.

The arteries of those who were most depressed had narrowed twice as much as those who were least depressed, the study found.

Hardening of the arteries can be a precursor to a heart attack or stroke and may occur because of a malfunctioning nervous system in depressed people, Stewart wrote.

Depression may also upset the body's regulation of glands that release chemicals governing energy level and growth, and alter the functioning of cells responsible for blood clotting.

Hardening of the arteries leads to an overreaction of the immune system and the resulting inflammation is known to release chemicals that can have effects on behavior, he added. The brain, too, can suffer from the reduced blood flow, reinforcing the depression and the resulting ailments, he wrote.

In the same journal, a British study of 46,136 severely mentally ill people found those who were younger than 50 were more than three times as likely to die from coronary heart disease and stroke than people not suffering from mental illness. Mental illness more than doubled the risk of dying from heart disease for people up to age 75.

The risk of dying from heart disease was even higher among those taking antipsychotic medication, and study author David P.J. Osborn at the Royal Free and University College Medical School, London.

Osborn urged a more "holistic" approach to caring for the mentally ill, with more frequent monitoring of such vital signs as blood pressure and cholesterol and more attention to diet and exercise that often go neglected.

A third study found that a persistent feeling of loneliness among the elderly doubled their risk of developing Alzheimer's-like symptoms compared to those who felt connected to others.

Autopsies on 90 of the study participants who died - the only sure diagnosis - did not turn up the tell-tale plaques, tangles and brain tissue damage of Alzheimer's, however.

That finding suggested something else to study author Robert Wilson of Rush University Medical Center, Chicago. He wrote that depression from loneliness somehow damaged the brain's ability to compensate for the age-related deterioration of the pathways that underlie social behavior and induced dementia.