London The development of allergies in children may be related to the age at which their mothers started having menstrual periods, new research suggests.
The prevalence of allergies and asthma has increased by as much as 80 percent in the developed world over the last decade or so, particularly in children, and scientists can't explain most of the increase. On average, 20 to 25 percent of people in the United States and elsewhere in the developing world have asthma or some other allergic disorder.
A study published this week in the British medical journal Thorax found that allergies were more common among people whose mothers started menstruating early and less prevalent among those whose mothers had their first period later, particularly after age 15. It is the first time such a link has been made.
The younger their mothers were when they had their first period the more likely the subjects were to have allergies as adults.
Dr. Baizhuang Xu, who led the study at Imperial College, London University, said his preliminary findings support the idea that the female sex hormone estrogen may play a role in allergies.
Puberty is triggered in girls by an increase in estrogen and experts have noted that girls are reaching puberty earlier these days.
Previous studies have suggested that women with high estrogen concentrations may be more likely to suffer allergies and that conditions in the womb might influence the development of allergies later in life.
Allergies and asthma are more prevalent in young boys than girls, but by puberty, the opposite is true.
Women have a higher incidence of allergies than men until the age of about 40 or 50, when menopause sets in. The prevalence of allergies is balanced equally between men and women after that age, except for women who are taking hormone replacement therapy, Xu noted.