Girls with more body fat experienced earlier menarche and hormone changes, but later full breast development, compared with those with normal weight, according to longitudinal data from 90 girls aged 8-15 years.
A link between obesity and early puberty has been observed among U.S. girls for decades, but more recent studies suggest that “girls with greater childhood adiposity have earlier thelarche and progress through puberty at a faster rate than normal weight girls,” wrote Madison T. Ortega, MD, of the National Institute of Environmental Health Sciences, Durham, N.C., and colleagues. However, studies involving hormone levels have yielded mixed results, they said.
In a study published in the Journal of Clinical Endocrinology & Metabolism , the researchers followed 36 girls with overweight or obesity and 54 girls with normal weight for 4 years; normal weight was defined as body mass index in the 5th to 85th percentile, overweight was defined as BMI in the 85th to 95th percentile, and obese was defined as greater than 95th percentile. Overweight and obese were combined into one category for comparison with normal weight girls.
Participants had an average of 2.8 study visits during this period and provided additional information by phone and online. Visits included measurement of total body fat using dual-energy x-ray absorptiometry (DXA), Tanner staging, breast ultrasound for morphological staging (BMORPH; A-E), pelvic ultrasound, hormone tests, and menarchal status assessment.
Overall, girls with overweight/obesity (OW/OB) had significantly more advanced breast development at baseline than did those with normal weight (NW), but these girls progressed through BMORPH stage D later than did NW girls. Early-stage breast development was not affected by total body fat. However, “an increase of 5 percentage points in mean total body fat, for example, was associated with a 26% decrease in the transition rate out of stage D,” the researchers noted.
Hormone levels were similar at baseline for follicle-stimulating hormone, inhibin B, estrone (E1), total and free testosterone, and androstenedione. However, these levels increased more quickly after 1 year for girls with OW/OB, while they plateaued in girls with NW and dropped among girls with lower total body fat. Total body fat had no apparent effect on other reproductive hormones including luteinizing hormone, modified vaginal maturation index, and estradiol 2.
The average age of menarche was 12.4 years across all participants, but girls with higher total body fat at baseline were more likely to reach menarche at a younger age. “For every 1-unit increase in visit one total body fat, the chance of achieving menarche at any given time point was 3% higher,” the researchers said. No interaction appeared between race and total body fat with regard to menarche.
Several surprising findings
The study is important because “there have been no longitudinal studies in U.S. girls to examine how total body fat affects serum reproductive hormones or the development of the breast and ovaries using ultrasound imaging,” corresponding author Natalie Shaw, MD, of the National Institute of Environmental Health Sciences, said in an interview.
Dr. Shaw said she was surprised by several of the study findings. “Others have reported increased male-like hormones (androgens) in overweight/obese girls in cross-sectional studies; however, we were surprised to find that FSH and inhibin B were also elevated in girls with excess body fat,” she said. “We also found, unexpectedly, that even though the breast bud appears earlier in overweight/obese girls (thelarche), which signals the onset of puberty, the breast matured more slowly during the course of puberty in overweight/obese girls compared with normal weight girls,” she noted.
“The main take-home message is that puberty looks different in girls with excess body fat; they develop breast tissue earlier, yet take longer to achieve a fully mature breast, and they undergo menarche earlier,” Dr. Shaw said. Clinicians should be aware of the hormonal differences based on body fat, Dr. Shaw emphasized. “Girls with greater body fat had higher levels of FSH (a pituitary hormone), inhibin B (an ovarian hormone), and male-like reproductive hormones (e.g., testosterone) that are made by the adrenal glands and the ovaries in the late stages of puberty,” she said.