The research by psychologist John Cacioppo and his colleagues' from the University of Chicago shows that the impact of loneliness on premature death is nearly as strong as the impact of disadvantaged socioeconomic status, which they found increases the chances of dying early by 19 per cent.
A 2010 meta-analysis showed that loneliness has twice the impact on early death as obesity does, Cacioppo said.
The researchers looked at dramatic differences in the rate of decline in physical and mental health as people age.
Cacioppo and his colleagues examined the role of satisfying relationships on older people to develop their resilience, the ability to bounce back after adversity and grow from stresses in life.
The consequences to health are dramatic, as feeling isolated from others can disrupt sleep, elevate blood pressure, increase morning rises in the stress hormone cortisol, alter gene expression in immune cells, increase depression and lower overall subjective well-being, Cacioppo said.
"People have to think about how to protect themselves from depression, low subjective well-being and early mortality," he said.
Evolution encouraged people to work together to survive and accordingly most people enjoy companionship over being alone, researchers said.
The research identified three core dimensions to healthy relationships: intimate connectedness, which comes from having someone in your life you feel affirms who you are; relational connectedness, which comes from having face-to-face contacts that are mutually rewarding; and collective connectedness, which comes from feeling that you're part of a group or collective beyond individual existence.
It is not solitude or physical isolation itself, but rather the subjective sense of isolation that Cacioppo's work shows to be so profoundly disruptive.
Older people living alone are not necessary lonely if they remain socially engaged and enjoy the company of those around them.
Some aspects of ageing, such as blindness and loss of hearing, however, place people at a special risk for becoming isolated and lonely, he said.
The research was presented at the American Association for the Advancement of Science's annual meeting in Chicago.