A new study has revealed that loneliness not only makes people unhappy but affects their mind also – in fact, it raises blood pressure and stress levels, general wear and tear, and the chances of developing Alzheimer's disease.

Moreover, the study has found that social isolation reduces a person's will power and perseverance, thus affecting their ability to follow a healthy lifestyle.

According to lead researcher Prof John Cacioppo of the University of Chicago, healthwise, the difference between a lonely person and a popular person is akin to "a smoker and a non-smoker".

"Loneliness not only alters behaviour, but loneliness is related to greater resistance to blood flow through your cardiovascular system. Loneliness leads to higher rises in morning levels of the stress hormone cortisol, affects the immune system, higher blood pressure and depression.

"The lonely have poor health. They exercise less, are more likely to quit. Eat more calories. They comfort eat more fats and sugars. Loneliness also lowers the ability to control yourself" Prof Cacioppo was quoted by 'The Daily Telegraph' as saying.

In fact, Prof Cacioppo and colleagues traced the need for connection to its evolutionary roots. In order to survive in the past, humans needed to bond to rear their children. In order to flourish, they needed to extend their altruistic and cooperate, they concluded.

Just as physical pain is a prompt to change behaviour, such as moving a finger away from the fire, loneliness evolved as a prompt to action, signalling an ancestral need "to repair the social bonds".