The age at which your mother began having periods could affect whether you suffer allergies, say researchers.

This could be explained by the influence of the mother's hormone levels on the development of the child.

The study of Finnish families was based on measurements taken more than 30 years ago.

More than 5,000 pregnant women had been asked about the age at which they began menstruating.

More recently, their thirty-something children were given allergy tests against types of grasses and house dust mites.

These figures were adjusted to take account of other factors that can affect the development and severity of allergies, such as maternal age, smoking, the season of birth, parental allergies and socioeconomic status.

The researchers found that mothers whose periods started younger than 12 were almost one and a half times more likely to have children who later developed allergies than mothers who started menstruating at 16.

Unclear why

The pattern was confirmed by looking at the ages in between - the higher the age at first periods, or "menarche", as doctors call it, the less chance of allergies for the children.

The study authors said: "To our knowledge, this is the first report of such an association.

"However, the biological mechanism underlying this finding is not clear.

"It is possible that differences in the maternal oestrogen environment, represented by varying age at menarche, could programme the immune system of the fetus."

Although there is a suspicion that hormone levels are key to this, there was no association between the age that the girl children had their first periods, and their allergies.

The study was reported in the journal Thorax.