People who are alone and lonely are at greater risk of heart disease
People who are alone may be less likely to eat well, exercise and see the doctor
Carina Storrs | 4/21/2016, 3 p.m.
(CNN) Loneliness and social isolation can impact a person's health, causing problems ranging from high blood pressure and being overweight to cognitive decline and even an increased risk of dying at a young age.
New research 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 stud,y 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.