Mother's age, not diet, determines a girl's menarche--study

The new study dispels the previously held thought that the average age of menarche, which is in between 11 to 12 years, has been falling as a result of childhood obesity, faster growth, and their bodies maturing early.

Scientists at the Institute of Cancer Research, a college of the University of London, have claimed that a woman’s age of menarche is significantly linked with that of her relatives, including her mother, older sister, grandmother or aunts, the Daily Mail reports.

Researcher Danielle Morris of the ICR said, “Our study findings suggest that genetic factors have a major influence on the age women in the UK begin menstruating, and these could have an impact on breast cancer risk.”

26,000 women studied
For the present study, the researchers analyzed data from women participating in an ongoing cohort study Breakthrough Generations, a major UK-wide investigation into the causes of breast cancer, who had atleast one female relative also involved in the study.

The participants were asked to complete questionnaires relating to the age when they started their periods, weight and height at the age of seven, and the amount of exercise.

Researchers used statistical method called linear regression to find the link between younger relative's age at menarche with their older relative's age at menarche.

The study, published in the peer reviewed medical journal 'Paediatric and Perinatal Epidemiology' was funded by Breakthrough Breast Cancer, the Sir John Fisher foundation, and the Institute of Cancer Research.

Findings of the study
Researchers found that hereditary factors within family explain half of the variations between women's ages when their first menstrual cycle started.

Interestingly, the mathematical modelling revealed that genetic factors accounted for 57 percent of the variation in the age of menarche in the women. Remaining was governed by environmental and lifestyle factors.

For each 12 month delay in age at menarche of an older sibling, mother, or paternal aunt, there was a three month delay for the younger relative, the study found.

Morris said, “The age at which a girl’s mother or older sister began their periods is the strongest clue as to when she will start.

“The effect exerted by a paternal aunt was unexpected but shows there is something genetic going on which we can’t yet explain."

The age at which menstruation begins is important as studies have linked it with the breast cancer risk. Experts aver that breast cancer risk increases with the early onset of menarche and older age at menopause.