Results of an NIEHS study do not support the idea that overweight girls are going through puberty earlier than normal weight girls because of estrogen made by excess fat tissue.

The findings, published online Aug. 28 in the International Journal of Obesity, are the product of the Body Weight and Puberty Study, the first pediatric study involving humans ever conducted at the NIEHS Clinical Research Unit. The goal of the research is to understand how obesity affects the timing of puberty in girls.

The NIEHS Body Weight and Puberty Study will help to show whether overweight girls enter puberty earlier than normal weight girls.

Scientific curiosity

Natalie Shaw, M.D., is the lead researcher for the project and head of the NIEHS Pediatric Neuroendocrinology Group. When she came to NIEHS in 2015, she wanted to understand why overweight and obese girls appeared to develop earlier than their normal weight peers.

Other scientists had proposed that overweight girls may undergo puberty earlier because estrogen, which can be made in fat tissue in addition to the ovaries, was speeding it up.

Shaw and her team set out to determine whether it was true that fat tissue was increasing estrogen and accelerating puberty. However, for ethical reasons, they could not take fat biopsies from the healthy girls enrolled in the study. So, they used several indirect approaches.

Those methods included breast ultrasound to determine the stage of breast maturity, mass spectrometry assay to measure reproductive hormone levels, and dual energy x-ray absorptiometry (DXA), a non-invasive test that uses x-rays to measure body composition.

DXA accurately measures percent body fat, whereas a calculation of body mass index does not, according to Shaw.

Precision is key

Shaw said for these types of studies, it is important to compare lean and heavy girls who are at the same stage of puberty.

Previously, researchers determined the stage of puberty by either inspecting or touching the breast, known as palpating. Although inspection and palpation are clinically accepted ways to determine puberty, they are not the most precise.

'Other studies measured estrogen levels in overweight and normal weight girls and didn’t find a difference,' Shaw said. 'Yet, people still hung on to that hypothesis.' (Photo courtesy of Steve McCaw)

'We used both physical exam and breast ultrasound to determine breast stage and morphology, so we could say with confidence that we were matching girls with normal weight or overweight of the same pubertal stage,' Shaw said.

A total of 80 girls, 54 normal weight and 26 overweight, from across the Raleigh-Durham-Chapel Hill area of North Carolina participated. The team did not see any difference in blood estrogen levels between the two groups, suggesting that the extra fat tissue in overweight girls was not producing estrogen.

The researchers also tried to determine whether breast fat contributed to breast development in overweight girls. According to Shaw, it follows that if their breast fat produced more estrogen, less estrogen would be circulating in their blood, resulting in smaller reproductive organs.

However, Shaw and her colleagues found no size differences between overweight and normal weight girls’ reproductive organs.

More to come

The published findings are the results of the participants’ first study visit. Shaw and her team have been tracking the girls for approximately 4 years. They have seen many girls five or six times, so they have data on their development, hormone levels, and the time of their first menstrual period. They are already working on writing up that long-term data for a second manuscript.

Vanessa Flores Poccia was a National Institutes of Health Undergraduate Research Scholar when she was a member of Shaw’s group and was involved in the study at its inception. Flores Poccia is a co-author on the paper and remains actively involved in the project as a special volunteer. She said that early puberty in girls is a topic of great concern for parents.

'Our hope is that the findings of this study can help promote dialogue between parents, young girls, and their healthcare providers,' Flores Poccia said.

Citation: Carlson L, Flores Poccia V, Sun BZ, Mosley B, Kirste I, Rice A, Sridhar R, Kangarloo T, Vesper HW, Duke L, Botelho JC, Filie AC, Adams JM, Shaw ND. 2019. Early breast development in overweight girls: does estrogen made by adipose tissue play a role? Int J Obes (Lond); doi: 10.1038/s41366-019-0446-5 [Online 28 August 2019].