Timing of puberty varies by up to 14 months among Asian youth

Among Asian youth, the onset of puberty can vary by up to 14 months across ethnic subgroups, a new Kaiser Permanente study shows. These early life variations could potentially help explain disparities in chronic health conditions that are seen in Asian adults.

“The population most researchers typically refer to as ‘Asian’ comes from many different places and has many different cultures and traditions that can impact health from childhood through adulthood,” said first author Ai Kubo, MPH, PhD, a research scientist at the Kaiser Permanente Division of Research. “This is the first study that’s been done to analyze pubertal onset by Asian ethnic subgroup and our findings show why this research is needed.”

The study, published May 13 in JAMA Network Open, looked at pubertal timing among 107,325 Asian American, Native Hawaiian, and Pacific Islander boys and girls who were members of Kaiser Permanente Northern California. The youth were categorized into 9 ethnic subgroups, based on self-reported information: Asian Indian, Chinese, Filipino, Japanese, Korean, Native Hawaiian and Pacific Islander, Vietnamese, Other South Asian, and Other Southeast Asian.

Each child had pubertal development assessed during routine primary care appointments. The researchers looked at age of pubarche (initial growth of pubic hair) and thelarche (initial breast development) in the girls, and at pubarche and gonadarche (testicular growth) in the boys. The research team also determined each child’s body mass index prior to starting puberty.

Among the girls, the overall median age at pubarche was 10.98 years. But there were distinct variations: pubarche started earliest in the Other South Asian group at a median age of 10.30 years while the Korean girls median age of pubarche was 11.49 years, a difference of 14 months. Similarly, the overall median age of thelarche was 10.13 years, but the timing ranged from a median of 9.80 in Native Hawaiian and Pacific Islander girls to 10.47 years in Korean girls, a difference of 8 months.

Among the boys, median age of pubarche was 12.08. But there were also distinct variations. Pubarche began earliest in Native Hawaiian and Pacific Islander boys at a median age of 11.72 years while Chinese boys had the latest median pubarche at 12.37 years, a difference of 8 months. Less variation was seen for gonadarche: the median age was 11.54 years, with the timing ranging from 11.31 years in Native Hawaiian and Pacific Islander boys to 11.66 years in Chinese boys, a difference of 4 months.

“The differences between the ethnic subgroups is a novel finding,” said study co-author Louise C. Greenspan, MD, a pediatric endocrinologist with The Permanente Medical Group. “Future analyses will be needed to see if this is a reflection of environmental exposures and lifestyle factors or if this is more genetic in origin.”

Puberty starting earlier

Throughout the world, girls are starting puberty earlier than they used to. Among girls, earlier puberty is associated with a higher risk of behavioral and emotional problems in adolescence and a higher risk of cancer, type 2 diabetes, and cardiovascular disease as adults. For boys, there is some evidence to suggest earlier puberty is tied to an increased risk of behavioral problems in adolescence and cardiovascular disease, diabetes, and prostate and testicular cancers as adults.

Previous studies that have looked at pubertal timing have found ties between weight, body mass index, and pubertal onset, with children at higher weights more likely to start puberty earlier. To see if that was driving their findings, the research team did a secondary analysis that included only the youth with a healthy body mass index. That analysis found variations in timing of puberty onset still differed significantly among ethnic Asian subgroups.

“These findings suggest that lifestyle factors like diet and physical activity, genetics, and metabolic or social factors contribute to disparities in pubertal timing,” said Kubo. “Body mass index is certainly a contributor, but it’s not the only reason that we see disparities across race or within ethnic subgroups.”

Race and ethnicity

Researchers have typically looked at race and ethnicity broadly, dividing study populations into the categories white, Black, Asian, and Latino. Racial and ethnic disparities seen in health care usage and health outcomes have led to discussions on the best way to integrate and analyze race and ethnicity in health research. More recently, there has been an increase in awareness about health disparities that are likely to be missed when studies do not separate the Asian population into Asian ethnic subgroups.

“Asian youth are often overlooked or not included in puberty research,” said senior author Julianna Deardorff, PhD, an adjunct investigator with the Division of Research and a professor at University of California, Berkeley. “Those studies that do include Asians rarely have sufficiently large numbers, and they are not representative of the diversity of Asian subgroups in the U.S. Our findings are a critical first step towards understanding pubertal development among Asian boys and girls.”

Added Kubo: “I didn’t expect that we would see up to more than a year’s difference in the timing of puberty. This study shows us that when you look only at the overall median, you can potentially miss an ethnic subgroup that is at higher or lower risk. Our findings also suggest we need to do additional research to explore whether the ethnic subgroup differences in pubertal timing correspond to disparities observed in increased risk of type 2 diabetes in adolescence as well as rates of gestational diabetes, type 2 diabetes, cardiovascular disease, and cancer in Asian adult ethnic groups.”

The study was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

Co-authors include Sara Aghaee, MPH, Lawrence H. Kushi, ScD, and Charles P. Quesenberry, Jr, PhD, of the Division of Research; Julia Acker, MS, of the University of California, Berkeley; and Shylaja Srinivasan, MD, and Alka M. Kanaya, MD, of the University of California, San Francisco.