Feeling lonely and isolated can do more than make people feel bad. It can be bad for their health, according to an accumulating body of scientific research.

Among the findings:

- The toll loneliness takes accumulates with time and goes right down to the cellular level, according to longtime loneliness researchers Louise Hawkley and John Cacioppo at the University of Chicago.

- Lonely middle-aged and older people report more chronic stress and felt more helpless and threatened than non-lonely people with the same number of stressful challenges, they report in the August 2007 issue of Current Directions in Psychological Science.

- Blood pressure was 16 points higher in lonely people over 65, suggesting diminished long-term health, according to their earlier work.

- Loneliness is linked to accelerated wear and tear on the body, and interruption of restorative sleep, reports Science Daily. Even college-age lonely people had poorer quality sleep.

- Longevity increased by 22 per cent among people 70 and older with a large circle of friends compared to those with the fewest among 1,500 older people in a 10-year study by the Australian Centre for Aging Studies.

- The weakest immune response to flu vaccine among young people is found in the most isolated and lonely first-year university students, Health Psychology reported in 2005 .

- Alzheimer's disease is twice as likely to develop in lonely people, although the link is not well understood, says a study published this year in the Archives of General Psychiatry.

- Thinking about suicide and self-harm increased with the degree of loneliness, according to a University of Montreal population-wide survey in 2001.

- The number of Americans saying they have no one to discuss important matters with increased from 11 per cent to 25 per cent in less than 20 years, according to a 2006 paper called Social Isolation in America by sociologists at Duke and the University of Arizona.