MSPs are to hold an inquiry into the effect of loneliness and isolation amid warnings that a lack of social connections is as harmful to health as smoking 15 cigarettes a day.

The Scottish Parliament's equal opportunities committee is to focus on under-25s and over-50s, as research suggests it is members of these two groups who are most at risk.

The committee is calling for young and older people who have experienced loneliness to come forward and contribute their views, as well as the charity, health and social service staff who may work to support them.

Margaret McCulloch MSP, convener of the Holyrood committee, said the effects of loneliness could be "devastating".

"We want to encourage best practice on combating the effects of loneliness to be shared as widely as possible," she said.

It comes amid a growing body of research suggests that loneliness can impact negatively on mental and physical health.

A study published by the University of Cambridge in 2010 compared social isolation with smoking, saying that being socially disconnected, with few good friends or strong family relationships, was equivalent to smoking 15 cigarettes per day.

According to Age UK, more than 80,000 Scottish over-65s say they always or often feel lonely, while 39 per cent or about 350,000 say the television is their main source of company.

Meanwhile the NSPCC's ChildLine helpline service counsels more than 5,000 children a year whose main problem is loneliness, sadness and isolation. Another 4,000 told the charity loneliness was among their worries.

One pensioner said it had made "all the difference" to receive help after the death of her husband Alex several years ago.

Bunty Dickson, 84, of Motherwell, said: "We were always together. After he was diagnosed with dementia, I cared for him for six years and it could be hard. But I just felt lost after he was gone. The loneliness was terrible."

Mrs Dickson's GP referred her to one of North Lanarkshire's local link officers, Luke, who eventually persuaded her to attend a local group of people her age.

"My daughter has been so impressed by the way my confidence is coming back," she said. "I still get anxious and nervous. But having Luke's support and new and old friends around me makes all the difference."

Ms McCulloch said MSPs wanted to know how much loneliness there is in both rural and urban communities,and where it is most likely to occur, as well as the best tactics for tackling it.

"The key questions for the committee are: what is the impact of loneliness and social isolation, is this an escalating problem and how can it be tackled effectively?"

The deadline for submitting views and experiences to the EqualOpportuntiesCommittee is March 13, and the group is expected to produce a report on its findings and policy recommendations in the summer.