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Feeling lonely seems to go hand in hand with being isolated, but there’s a difference, according to a growing body of research.

It’s no secret that people who are socially isolated tend to be at greater risk of health issues, from mood disorders like depression to stress-related chronic conditions like heart disease. But what is really responsible for these negative outcomes — the emotional toll of feeling alone or the physical and social lack of contact with others?

Now a new study suggests that being socially isolated may have a greater effect on risk of early death, especially among the elderly. The research, which was led by Andrew Steptoe, a professor of epidemiology and public health at University College London, followed 6,500 British people over 52 from 2004 until 2012. The most socially isolated in this group were 26% more likely to die during the study period than those with the most active social lives, even after controlling for factors that also affect mortality, like age and illness.

(MORE: How Feeling Lonely Can Shorten Your Life)

In contrast, feelings of loneliness reported by the participants, although often linked with isolation, were not significantly linked with death risk when these other factors were taken into account. Separating out the two influences is important because therapies to change perceptions of loneliness aren’t likely to work if the real problem is not having friends or family who can provide support.

“This finding suggests that the subjective experience of loneliness — often thought to be the psychological manifestation of social isolation — is not the primary mechanism explaining the association between social isolation and mortality,” the authors conclude.

They offer several explanations for the health risks linked to isolation. First, being isolated may mean that no one else is aware of the first signs of illness, or worsening symptoms of a disease, which can delay medical attention and lead to earlier death.

(MORE: Loneliness, Not Living Alone, Linked to Dementia)

But more important, social contact can have profound physiological effects. Simply holding a loved one’s hand lowers blood pressure and reduces pain, for example. Studies show that lack of affectionate physical contact is associated with higher levels of stress hormones and inflammation. “Social contact itself also may have specific biological consequences that are important for health maintenance,” the authors write.

Indeed, loneliness may be a marker for health problems that arise from such social isolation, and previous studies have conflated loneliness and social isolation. “These results do not imply that loneliness is not important,” the authors note, “but rather indicate that the experience of loneliness may be characteristic of people who already have major health and mobility problems.”

John Cacioppo, director of the Center for Cognitive and Social Neuroscience at the University of Chicago, calls the new findings “exciting” but believes there are other ways that loneliness may contribute to early risk of death. He says that cultural differences, for example, may account for some of the negative effect on health. “For instance, the Brits’ culture of a ‘stiff upper lip’ may mean people who live alone are less likely to admit to feeling lonely than are residents of the U.S.” That would make it harder to separate out the results of loneliness and isolation in a British sample, he says.

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But regardless of whether it’s the physical isolation of individuals or their loneliness that contributes to poor health, people who feel as if they are alone in the world are at increased risk of early mortality. “Both objective and subjective isolation can imprison an individual, though through different means,” says Cacioppo.

The results therefore have important implications for addressing those who are isolated. They suggest that physically engaging people who are socially apart may do more for improving their health and survival than trying to address their feelings of loneliness or feeling left out. All it takes is a walk or a lunch or even a hug.