SUNDAY, May 1, 2005 (HealthDay News) -- Scientists may have uncovered a reason why men who are socially isolated tend to have more cardiovascular disease.
Those without adequate support networks had elevated levels of interleukin-6 (IL-6), a molecule that signals inflammation linked to cardiovascular disease, according to findings that were to be presented Sunday at the American Heart Association's annual conference on cardiovascular disease, epidemiology and prevention in Washington, D.C.
The link did not hold true for women, however.
And experts treated the findings with caution. "I don't see this as convincing enough yet to tell me this is the common link between social isolation and behavioral abnormalities and cardiovascular risk, but it's intriguing and deserves further study," said Dr. Richard Milani, section head of preventive cardiology at the Ochsner Clinic Foundation in New Orleans.
The idea that men with better social integration have less heart disease is not a new one -- data over more than two decades has shown the link, according to experts. But the authors of this study were trying to find the biological mechanisms behind the connection.
The study involved 3,267 men and women, average age 62, who were participating in the Framingham Heart Study.
To gauge the level of social connection, the participants were also asked about their marital status; the number of relatives and close friends they felt they could confide in; whether they attended religious meetings or services; and whether they participated in groups like those at senior centers.
Researchers then measured blood concentrations for four inflammatory markers, including IL6, in each participant. Inflammation appears to play a role in atherosclerosis by allowing fats to build up in blood vessel walls.
Men with the lowest levels of social involvement had the highest levels of IL-6. In women, however, there was no association between social networks and IL-6 levels.
There also appeared to be no association between social involvement and three other markers of inflammation: C-reactive protein (CRP), soluble intercellular adhesion molecule-1 and monocyte chemoattractant protein-1.
IL-6 may be raised in men who are socially isolated for two reasons, the authors said. Social isolation may spur such behaviors smoking or physical inactivity, which affect IL-6 levels, or it may contribute to depression or stress, which can contribute to increased IL-6 levels.
But the fact that social isolation was only associated with one inflammatory marker troubled the experts.
"IL-6 is the pathway for CRP, and they should be moving together," said Dr. Robert J. Myerburg, a professor of medicine and physiology at the University of Miami School of Medicine. "I don't know how to interpret that. Either they're on to something really hot biologically, or there's an error."
"I would have expected to see CRP levels and some other things change as well," Milani added.
Observed gender differences also raised questions.
Milani hypothesized that it simply might be more difficult to study social relationships in women than in men. "Men are probably easier to pin down in terms of social network," he said. "Women are more complex."
Study author Eric B. Loucks, an instructor at the Harvard School of Public Health in Boston, suggested that relationships might mean something different for women, and could even constitute a stressor for them.
"We're finding gender differences in biological pathways," he said.
Knowing the missing link between social isolation and heart disease might help target and refine therapies. "We could use it to see if an intervention [such as psychotherapy] is working," Milani said.
"We can better gauge the health effects of an intervention rather than waiting years to see if heart disease develops," Loucks added.
For more on atherosclerosis, visit the American Heart Association.