has now put a number on how this can affect someone's risk of heart disease and stroke specifically.
Researchers at the University of York found that people who are isolated -- meaning they have few social connections -- or feel lonely have a 29% higher risk of having heart disease and 32% higher risk of having a stroke when compared with their peers who were either well connected or at least felt like they were well-connected.
To arrive at these numbers, researchers combined data from 23 studies that altogether included more than 180,000 adults living in high-income countries in North America, Europe, Asia and Australia.
The studies had assessed the level of isolation and loneliness among the participants and monitored them for between three and 21 years to see whether they developed heart diseases, such as a heart attack, or suffered a stroke.
In most cases, it was participants' first heart attack or stroke.
"We know from other studies ... that people who are lonely or isolated are less likely to recover [from illness]," said Nicole K. Valtorta, research fellow in public health, who led the study published Monday in the journal Heart
"From our study, we are saying it is not just about people who are already sick, but prior to that they might be at risk of developing disease," she said.
Does loneliness drive heart disease and stroke?
The research puts loneliness and social isolation on par with anxiety
as a risk factor for heart disease and stress
at work as a driver of stroke risk.
The level of risk does, however, remain lower than that of smoking cigarettes, which increases the risk of heart disease by two to four times
. The studies in the analysis made the assumption that smoking was a separate risk factor for heart disease and stroke than isolation and loneliness, but the two could be associated.
"It could be that loneliness and social isolation are linked to an increased risk of smoking, so it's not as though the smoking risk is necessarily independent of [them]," Valtorta said.
How health can deteriorate
There are many ways that being lonely and isolated can influence health and the onset of a variety of diseases, including heart conditions. For example, people who are on their own could have worse diets or not exercise or sleep as much; they could also be less likely to take medications or see a doctor.
All of these factors, or just the stress and sadness of being alone, could drive up blood pressure and inflammation, which in turn could lead to heart disease. Previous studies
have found that people who were less socially connected had higher blood pressure as well as higher levels of a marker of inflammation their blood.
"Being alone, or feeling like you are alone, probably increases the risk of many diseases by about 30%," said Julianne Holt-Lunstad
, associate professor of psychology and neuroscience at Brigham Young University.
Holt-Lunstad wrote an editorial
about the research, also published in Heart, in which she states it is particularly important to find out how loneliness and social isolation can affect heart disease because it is the leading cause of death in the United States.
"This study helps build the knowledge base" said Holt-Lunstad.
More research is needed to identify the true role of social relationships in both cardiovascular and general health. In the study, Valtorta adds that it is not possible to state that loneliness and social isolation directly increase heart disease or stroke risk. There could be other ways that people who are less connected differ from those who are well connected, which could contribute to their risk.
Loneliness and isolation also appear to take a toll on a person's lifespan, according to previous research
by Holt-Lunstad and colleagues. The team found that people with the fewest relationships, or who felt like they had the least social support, had a 50% higher risk of dying during the study period than those who were well-connected.
Valtorta was not able to parse out whether loneliness and social isolation were separately associated with heart disease and stroke risk in her study, because most of the studies they analyzed only looked at social isolation.
"[They] are very different things...there are people who are socially isolated but are fairly content ... and there are people who are constantly surrounded by people but still feel incredibly lonely," Holt-Lunstad said.
"I would suspect that if you are both, it is going to be associated with the highest risk, and if you are one or the other, it is going to be associated with the intermediate risk," she added.
How to stave off social isolation
A number of interventions
show promise for helping people make social connections or lifting them out of loneliness. One example is the use of therapy that focuses on improving social skills and programs that offer social opportunities, such as activities for older adults, which have been found to decrease loneliness.
Some areas of the United Kingdom are experimenting with a program called Reconnections t
hat targets older adults in the community that are at risk of becoming socially isolated and connecting them with social workers and members of the community who can help them find, and participate in, activities that interest them. The program is still being evaluated to find out if people feel more connected and if this then boosts their well-being, Valtorta said.
"That is one of the great unknowns, whether interventions can both benefit people's social relationships, but also benefit their health," Valtorta said.
One key challenge remaining for health care professionals is identifying people at risk of isolation in the first place. Holt-Lunstad urges clinicians to talk with patients about the importance of social connections for a healthy lifestyle and to recommend counseling or social support services. Medical organizations, such as the American Heart Association, should also add social isolation to the list of major risk factors for heart disease.
According to Holt-Lunstad said, further evidence is needed to ensure this. "Part of the hesitancy," she said. "There are still a lot of questions about what we do about it."