Only two in five people can smell asparagus in their urine after they have eaten it, a new study suggests.

Consuming the vegetable is commonly associated with producing a distinct smelling urine but new research found that 60% of the population cannot detect the scent.

A team of US and European researchers set out to discover why some people can detect the smell and others cannot after they were discussing the phenomenon at a scientific meeting in Sweden.

They examined data from almost 7,000 adults taking part in the Nurses' Health Study and Health Professionals Follow-up Study.

The study, published in The British Medical Journal, found that three in five could not detect the smell - this group was labelled "asparagus anosmic".

A higher proportion of women reported they were unable to detect the odour compared with men.

The researchers suggest it may be due to under-reporting by a "few modest women", or because they might be less likely to notice an unusual smell because of their position during urination.

The authors went on to examine the possible genetic differences between those who could pick up the scent and those who could not.

They found genetic variations between those who could not smell the vegetable in urine and those who could.

They discovered 871 particular variations in DNA sequence, known as single nucleotide polymorphisms, on chromosome 1 which were associated with being asparagus anosmic.

These genetic variants were found in several different genes responsible for sense of smell.

"Our findings present candidate genes of interest for future research on the structure and function of olfactory (sense of smell) receptors and on the compounds responsible for the distinctive odor produced by asparagus metabolites," they wrote.

"Future replication studies are necessary before considering targeted therapies to help anosmic people discover what they are missing."