A South Dakota State University study showed that women who began menstruating at an earlier age had a higher percentage of body fat as adults than women who began menstruating later.

But women who began menstruating earlier also had higher bone mineral density in the hip as adult women. They also had greater bone mass and bone density in the femoral neck region of the hip, a common site for hip fracture.

These are among the findings in a study by assistant professor Teresa Binkley at SDSU’s Ethel Austin Martin Program in Human Nutrition. Binkley worked on the project with Courtney Grimsrud, an undergraduate research assistant at the time, and professor Bonny Specker, director of the Ethel Austin Martin Program.

The SDSU researchers published the results of their study in 2008 in the American Journal of Human Biology. The study looked at the effect of menarcheal age on body size and bone measures in adult women.

“ ‘Menarcheal age’ refers to the age at which a female first begins menstruation,” Binkley explained.

“If the age at which a female starts menstruating, or her menarcheal age, is early, then she has an increased exposure to estrogen compared to a female with a later menarcheal age.”

Estrogen exposure leads to growth plate closure, or the stage at which bones stop growing in length, as well as to mineral packing in bone. Studies have associated early menarcheal age with increased bone density. Some research has also associated early menarcheal age with shorter stature and greater percent body fat as an adult, while later menarcheal age is associated with taller stature and leaner body composition.

The purpose of the SDSU study was to determine in adult women the effect of menarcheal age on weight, body fat, height, limb length and bone measurements.

To measure bones, the study used two technologies. Dual energy X-ray absorptiometry, or DXA, is used routinely in hospitals and clinics to measure bone density of the spine or hip. Peripheral quantitative computed tomography, or pQCT, is a method that measures density, size and shape of the arm or leg bones and is used for research purposes.

“Our hypotheses were that women with young menarcheal ages compared to those with higher menarcheal ages would have higher adult percent body fat and higher adult weight, shorter height and limb length, and greater bone mass and bone mineral density.”

The subjects were a subset of South Dakota Rural Bone Health Study, 260 women with regular menstrual cycles from two ethnic groups (140 were Hutterite, 120 were non-Hutterite). They ranged from 20 to 40 years old.

The study measured weight, standing height, sitting height (defined as the length from the stool seat to the top of the head), leg length (standing height minus the sitting height), and forearm length.

The study assessed menarcheal age by asking women in the study when they began menstruating. Fifty percent of the study participants said that was before age 13; the other 50 percent said it was at age 13 or after.

“Although it wasn’t in our hypothesis, we did find a trend in menarcheal age,” Binkley noted. “Women born in 1960 tended to have an older average menarcheal age than women born toward the 1980s,” Binkley said.

“Although it was not statistically significant, it is interesting that in this population, the trend over the 20-year-age-range was 2.3 months per decade.”

In line with their hypothesis, SDSU researchers found that women with younger menarcheal ages had on average a higher percent body fat as adults than women with later menarcheal ages. They also weighed more.

However, the study found no associations between menarcheal age and height, sitting height or limb lengths.

Interestingly, women with an early menarcheal age had a smaller bone size at the distal radius, the end of the arm bone near the wrist, than women with a later menarcheal age.

“Women with a later menarcheal age have more time for the adolescent growth spurt, and their bones probably grow bigger,” Binkley said.

The Ethel Austin Martin Program in Human Nutrition at SDSU and a grant from the National Institutes of Health supported the research.

Assistant professor Teresa Binkley at SDSU’s Ethel Austin Martin Program in Human Nutrition studied menarcheal age as a factor in body size and bone measurements in adult women.

Source: South Dakota State University