The problem of social isolation is now worse in Dublin than in rural areas.
One in three people over 50 in Ireland has struggled with some form of loneliness, a new report reveals today.
It has now reached the point where doctors need to include loneliness in their assessment of the health of a patient.
Loneliness is a particular blight on the lives of older people, affecting more men than women.
The findings from the Irish Longitudinal Study on Ageing (Tilda) in Trinity College highlight "worrying levels" of emotional loneliness among our growing older population and signal it is a critical issue for public mental and physical health.
Previous research by Tilda estimated as many as 400,000 people in Ireland suffer from varying degrees of loneliness.
The latest report found that loneliness does not always increase as we get older - it decreases from 50 to 67 years, before rising again.
Almost one in 10 adults aged 50 years and over in Ireland is socially isolated with one or fewer regular social contacts.
Nearly one in five of those who have high levels of social contact still report feeling lonely.
Those with the least education are twice as likely to be "most isolated".
Older people who live alone are almost twice as likely to be in the "most lonely" group compared to those who live with others.
The last census showed that the number of over-65s who live alone has risen to 156,799.
The emotional effect of living alone was stronger for men than women. Some 56pc of men who live on their own were in the "most lonely" category compared to 45.3pc of women.
People living in rural areas were less likely than those in Dublin city and county to be in the most isolated group.
Loneliness can negatively affect a person's health and more than three-quarters of the most lonely group reported clinically significant depressive symptoms compared to just 7.4pc of the least lonely group.
Dr Mark Ward, lead author and Tilda researcher, said: "Loneliness is a growing public health concern as there is clear evidence that feeling lonely is damaging to the health and well-being of older adults.
"This report highlights the fact that certain groups of older adults are particularly vulnerable to loneliness and social isolation. In particular, older adults who live alone are more socially isolated and report greater feelings of loneliness.
"Lonely individuals tend to have poorer health and quality of life, and loneliness is strongly linked to depression. This report provides clear evidence of the need to address loneliness in the older population. This is particularly important as we strive to make Ireland the 'best place in the world to grow older'."
Professor Rose Anne Kenny, principal investigator of Tilda and an author of the report, added: "This study shows the worrying extent of loneliness and social isolation among adults aged 50 years and older in Ireland.
"Loneliness is clearly damaging to the health and well-being of individuals and it is therefore critical that efforts are made to address this growing problem. This new research will help policy makers and others identify the most vulnerable groups in our society. This research also highlights the need for healthcare professionals to consider loneliness during clinical assessments of their patients."