People with heart disease who live alone tend to die sooner than those sharing their home with others, according to an international study that looked at more than 44,000 people.

Previous studies have linked social isolation to everything from heart attacks to weakened immune systems, but the current study, published in the Archives of Internal Medicine, focused specifically on people with known heart disease or at very high risk for it.

Reasons for the difference remain unclear, but lead researcher Deepak Bhatt said access to regular medical care might be involved.

"Patients living alone may have more difficulty getting their medications refilled and taking them regularly," Bhatt, at Harvard Medical School in Boston, told Reuters Health.

"They also don't have anyone at home to call the doctor's office or emergency room if they are not looking well."

The study included more than 44,000 people, all aged 45 or older, from multiple countries across the globe.

Over the four years the study lasted, 7.7 percent of participants younger than 65 who lived on their own died, compared to just 5.7 percent of those who didn't live alone.

The gap was smaller for people aged 66 to 80, but it remained statistically reliable even after accounting for age, sex, employment, ethnicity and country. The living situation of those over 80, however, wasn't tied to death rates.

Bhatt and his team speculated that in people under 80, living alone could signal psychological and social problems like job strain or loneliness. In contrast, very old people who live on their own may be healthier and more independent than those who don't.

Whatever the explanation, Bhatt said cardiologists should routinely ask their patients if they live alone.

"If the answer is yes, that might be a red flag and they should make sure the patients have a way to get their medicine regularly," he said.

Meanwhile, patients who live alone should think twice before ignoring changes that might be a sign of health problems.

"May times people just adapt to their circumstances. Perhaps just lower your threshold a little bit and realize it's better to call (the doctor) than not to call."

But that might not be the whole story, he acknowledged.

"Other mechanisms by which living alone could increase cardiac risk have to do with possible social isolation and loneliness, and these are more challenging to fix," he said.

Indeed, another report published along with Bhatt's shows that older people who felt lonely had more difficulty performing basic tasks of daily living and died younger than those who didn't feel alone.