Loneliness is not unique to the elderly - people in late 20s suffering, says study

The three main periods of loneliness have been revealed.

Researchers in the US found that people reported feeling moderate to severe loneliness during their late twenties, their mid-fifties and their late eighties.

The general sense of isolation was also more prevalent than the researchers expected.

Three out of four study participants reported moderate to high levels of loneliness - this figure represents a 'substantial increase' from previously reported prevalence estimates in the US general population, which have ranged from 17 to 57 per cent.

"This is noteworthy because the participants in this study were not considered to be at high risk for moderate to severe loneliness", said study leader Dr Dilip Jeste.

"The mid-50s is the midlife crisis period," he was quoted as saying by CNN.

"And the late 80s is, of course, a period when, if you're lucky to have survived to that age, then things start getting worse".

The study was conducted among 340 San Diego County residents, between the ages of 27 and 101.

Three quarters of all study participants reported moderate to high levels of loneliness.