Your heartbeat accelerates, you have butterflies in your stomach, you feel euphoric and a bit silly. It's all part of falling passionately in love -- and scientists now tell us the feeling won't last more than a year. REUTERS/File

ROME (Reuters) - Your heartbeat accelerates, you have butterflies in the stomach, you feel euphoric and a bit silly. It's all part of falling passionately in love -- and scientists now tell us the feeling won't last more than a year.

The powerful emotions that bowl over new lovers are triggered by a molecule known as nerve growth factor (NGF), according to Pavia University researchers. This brain chemical is likely to be responsible for the first flush of love.

Researchers said raised levels of a protein was linked to feelings of euphoria and dependence experienced at the start of a relationship.

The Italian scientists found far higher levels of NGF in the blood of 58 people who had recently fallen madly in love than in that of a group of singles and people in long-term relationships.

But after studying people in long and short relationships and single people, they found the levels receded in time.

The team analysed alterations in proteins known as neurotrophins in the bloodstreams of men and women aged 18 to 31, the Psychoneuroendocrinology journal reported.

As twelve months passed love became more stable, while romantic love seemed to have ended

But after a year with the same lover, the quantity of the 'love molecule' in their blood had fallen to the same level as that of the other groups.

The Italian researchers, publishing their study in the journal Psychoneuroendocrinology, said it was not clear how falling in love triggers higher levels of NGF, but the molecule clearly has an important role in the "social chemistry" between people at the start of a relationship.

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