Millennials are now far less likely to count a close family member such as a brother or sister among their best friends, according to a new study.
Greater numbers going to university, as well as leaving home to live in large cities, means family ties are being weakened, contributing to a "growing problem of loneliness among" current 20-somethings, the report by the Intergenerational Foundation concluded.
The research compared survey data from those in their 20s in 2015, 2005 and 1995, indicating that overall well-being for this age-group has declined by 10pc over the past two decades.
The report said social media enabling young people to communicate more with their friends, at the expense of their family, may also be contributing to the slump in in-family friendships.
Based on data from the British Household Panel Survey, the study found that in 2015 millennials were 80.9pc less likely to have a family member as one of their three closest friends compared with 1995, and 55.2pc less likely compared with 2005.
However, despite the connecting power of technologies such as Facebook and Instagram, levels of close friendship overall have declined by more than 6pc in the past 10 years.
The experts said this indicated that even though young people were spending large amounts of time online, they were not necessarily using this time to form meaningful friendships.
The survey also showed that young people now believe themselves to be 25pc less physically healthy than in 1995, despite exercising more frequently and drinking less alcohol.
The report found that, combined, the two may indicate increasing loneliness in young adults.
"If that is the case, then it should provide an important wake-up call that loneliness is a problem which affects people of all generations," the authors wrote.
"The decline in how young adults perceive their health status is striking and raises a host of important questions which should demand further investigation.
"Does it really reflect mental problems, such as anxiety and depression, which could be manifesting themselves in an unexpected way?
"Or is it more to do with genuine changes in the health of this age cohort, such as the rise in levels of obesity?"
Last week Facebook confirmed it would be introducing "digital well-being" tools that enable users to spend less time on the site as a means of combating addiction. (© Daily Telegraph, London)