"We can show that there are independent effects of various separate risk factors that have been brought up in debates and news about Covid-19," said study author Sven Drefahl from Stockholm University in Sweden.

"All of these factors are accordingly individually associated with a strongly elevated risk of dying from Covid-19," Drefahl added.

The study is based on data from the Swedish National Board of Health and Welfare on all registered deaths from Covid-19 in Sweden for adults aged 20 and older.

In a study, published in the journal Nature Communications, Drefahl explained that those born abroad generally have lower mortality than people born in Sweden.

This also applies when the research took income and level of education into account.

The elevated risk of dying from Covid-19 for this group remains after the researchers controlled for circumstances, such as income and level of education.

The study shows that being a man, having a lower income and lower level of education also result in a strongly elevated risk of dying from Covid-19. As to these aspects, this also agrees with the patterns for mortality from other diseases.

The findings showed that men had more than twice as high a risk of dying from Covid-19 than women.

Unmarried men and women (including those never married, widows/widowers and the divorced) had a 1.5-2 times as high risk of dying from Covid-19 as those who were married.

According to the researchers, men generally have higher mortality at comparable ages, which is considered to be due to a combination of biology and lifestyle.

"The fact that people with little education or a low income have higher mortality may largely be due to lifestyle factors, including finances -- how much one can afford to prioritise one's health," said study author Gunnar Andersson "Similarly, we can explain the elevated mortality from Covid-19 for these groups," Andersson added.

A number of earlier studies have also shown that single and unmarried people have higher mortality from various diseases, the research team noted.