Cole Porter was wrong - love only lasts a year!

According to scientists, those who say that true love lasts a lifetime have got it completely wrong and in fact it only lasts a year.

It seems that the giddy, intoxicating head-spinning feeling that engulfs lovers when they first meet, all comes down to a chemical in the brain which wears off after just 12 months.

What is more it seems that is the case even among couples who are still passionately in love.

The researchers from the University of Pavia in Italy, studied a group of men and women aged 18 to 31, some of whom had just fallen in love, some of whom were in long-term relationships and others who were single.

They found that amongst those in the first throes of passion, levels of a protein called Nerve Growth Factor, which is responsible for the palpitations, sweaty palms and butterflies indicative of passion, soared.

However in couples who had been together for a year or more, the levels had fallen back to that found in singles.

Dr Enzo Emanuele, who led the study says it has been demonstrated for the first time that circulating levels of NGF are elevated among subjects in love, which suggests it plays an important role in the social chemistry of human beings.

He says that potential lovers need to be truly, deeply, madly in love, and the raised NGF levels which occur when people fall in love could be related to specific emotions typically associated with intense early stage romantic love, such as emotional dependency and euphoria.

He suggests that NGF could be involved in the formation of novel bonds, but does not appear to play a major role in their maintenance.

The researchers studied volunteers whose relationships had begun within six months and they were asked to spend at least four hours a day thinking about their partner.

Tests showed that both men and women who had recently fallen in love had very high levels of NGF - 227 units, compared with 123 units recorded in those in long-standing relationships.

It was also apparent that those who reported the most intense feelings also had the highest NGF levels.

But when researchers revisited couples from the 'in love' group who were still in the same relationship more than a year later, they found that levels of NGF had declined to the same as those who were single or in a long-term relationship.

Prior to this study research on the chemical has focused on its impact on the nervous system, and its relationship with conditions such as Alzheimer's disease.

Dr Emanuele and his team appear to be the first to show a link between NGF and love, and the team believe that NGF plays an important part in the release of another chemical responsible for social bonding.

So even though the passion dies, the same chemical stimulates companionship essential in any long-term relationship.

The researchers conclude that considering the complexity of romantic love and its ability to exhilarate, arouse, disturb and influence behaviour so profoundly, further investigations on the neurochemistry and neuroendocrinology of this unique emotional state are justified.

The report is published in the journal Psychoneuroendocrinology.