Girls' BMI Determines The Start Of First Menstruation

By Margarita Nahapetyan

International team of scientists has revealed that there are two genes that help to determine when girls have their first menstruation. According to new findings, this genetic code also points to regulatory mechanisms that are involved in the growth and development of human body.

The investigators from the Peninsula Medical School, in collaboration with their colleagues from research institutions all across Europe and the United States, have for the first time identified two genes that are responsible in determining when girls begin menstruating. Scientists predict that one in every 20 females carry two copies of each of the gene variations which cause menstruation to begin earlier - approximately four and a half months earlier, compared to those who do not carry any copies of the gene variants.

In the western countries children are now reaching puberty at younger and younger ages - some girls even at the age of seven or eight. Many blame rising obesity rates because, in general, menstruation at an early age is also associated with shorter stature and increased Body Mass Index (BMI), and a higher ratio of fat compared to those who have their first period at a later time.

For the new study purposes, the researchers analyzed data on 17,510 women across 8 different international sources. This number also included women of European descent who reported at which age they had their first menstruation started. The age ranged between 9 and 17 years. When the experts assigned the women into the groups according to the age they began menstruating, they observed the appearance of certain gene patterns. Scanning the whole genome made it possible to hone in on these differences and pinpoint to the exact genes that are most likely responsible.

The lead investigator of the study, researcher Dr. Anna Murray said that their study provides with the first ever evidence that common genetic variants influence the time at which women reach sexual maturation. "Our findings also indicate a genetic basis for the associations between early menstruation and both height and Body Mass Index," she said.

Dr. Aric Sigman, psychologist and fellow of the Royal Society of Medicine, said that menstruation at an earlier age appears to be a health issue because besides being an inconvenient surprise for a girl and her parents, it is also linked to a higher risk of a number of conditions and psychological problems. Girls maturing earlier tend to develop depression, they are more likely to be delinquent, aggressive and socially withdrawn. These girls also develop sleep problems as well as drinking and smoking problems, drug abuse, lower self-esteem and have suicidal thoughts. Experts suspect that the female sex hormone estrogen which is produced at higher rates during a woman's reproductive life, contributes to the increased risk of these conditions, therefore, the earlier a girl goes through puberty, the more risk she may be at.

According to Dr. Sigman, girls who have their period very early are also more likely to have poor academic performance in high school, compared to their counterparts who have their first menstruation on-time or at a later time. "It is important that we understand why early menstruation occurs and these findings bring us closer to explaining this in some girls," he said.

The study is published in the latest issue of the journal Nature Genetics. Researchers from Harvard School of Public Health (HSPH), Brigham and Women's Hospital (BWH), National Cancer Institute (NCI), and the Broad Institute of Harvard and MIT were involved in the work.