Junkfood Science: <i>Junkfood Science Weekend Special:</i> Fears about early puberty in girls — Are they about fat or hype?

March 10, 2007

Junkfood Science Weekend Special: Fears about early puberty in girls — Are they about fat or hype?

A new study in the news this week purportedly showed “Childhood Obesity Triggers Early Puberty.”

As with most media stories nowadays, this one was reported almost verbatim from its press release. And, like most stories fueling popular alarm over childhood obesity, it was accompanied by photos of headless fat children. The lead researcher was quoted as saying: “Our finding that increased body fatness is associated with the earlier onset of puberty provides additional evidence that growing rates of obesity among children in this country may be contributing to the trend of early maturation in girls.”

To add to the growing list of fears surrounding “childhood obesity” as a public health crisis, the press release and most news stories ended with claims that “earlier onset of puberty can lead to higher rates of behavioral problems and psychosocial stress, as well as earlier initiation of alcohol use, sexual intercourse, and increased rates of adult obesity and reproductive cancer.”

Most unsettling were suggestions for weight control interventions for girls as young as 3 years old.

The saturation of media coverage, let alone the aggrandizement of the study’s significance and potential of harm from reacting to it, encourages us to consider cautiously and carefully what this study actually found and how its findings add to the evidence to date.

This study, published in the journal Pediatrics, applied data on 354 girls born in 1991 at hospitals in ten regions of the United States to look for associations between onset of puberty and weight status. The researchers used the database of the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development — a project begun to examine child behavior and development related to child care experiences.

Selective measures

Before we look at the actual results, several relevant notations were made by the researchers which affect how we can interpret their findings. First, they used only select measures to define early puberty in the girls:

(a) breast development at or more than Tanner stage 2 by physical examination at the grade 4 visit [age 9 1/2]

(b) breast development at or more than Tanner stage 3 by physical examination at the grade 5 visit [age 10 1/2]

(c) maternal report of breast development at or more than Tanner stage 3 at the grade 5 visit

(d) maternal report of menarche having already occurred (yes versus no) at the grade 6 visit [age 11 1/2]

For those unfamiliar with Tanner stages, they describe the physical changes children undergo during sexual growth and development. Each stage occurs at a different age and progresses differently among children.

As carefully noted by Dr. Scott Moses, M.D., a board-certified Family Physician practicing in Lino Lakes, Minnesota and author of the Family Practice Notebook, height is the first characteristic noted at each stage and increases most dramatically during the ages the girls in this study were evaluated: 7-8 cm a year! Height also has the biggest influence on BMI (body mass index), which is a calculation using height and weight, especially among growing children.

Yet, among the measures these researchers did not report, was the height of these girls. Instead they used BMI, a popular but inappropriate surrogate for “obesity” in growing children. The BMIs of all growing children increase, as they did in this study — most people believe that means today’s children are all becoming fatter. The role of height is never considered.

An interesting side note. The percentage of girls in this cohort who were labeled “overweight” during their grade school years varied from year to year with no consistency. Some were considered fat one year and not the next. Again, we are reminded that growth in children normally comes in unpredictable and completely individualized spurts and stops, and most careful medical professionals urge caution before ever jumping quickly to conclude that a child has a weight “problem.”

As has been reviewed, BMIs can especially misdiagnose girls entering puberty as being “too fat,” because it’s a time when it’s normal and healthy for them to gain 20 or more pounds in one year as their bodies prepare for childbearing, and for them to add up to 20 percent of their body weight in fat needed to begin normal menstrual cycles.

Another significant concern in this study is that the researchers noted that their physical evaluations for breast development at Tanner stage 2 did not include palpation. They admitted that mere observation could mistake fat for early breast development and lead to misclassifying heavier girls as being in puberty. Despite this clear problem, the measures for puberty were lumped together in their conclusions, leaving the public unable to separate out the potentially distorting stage 2 findings. This tactic would clearly further exaggerate any correlations with higher BMIs.

The findings

After throwing data from a database into a computer, the correlations statistically derived must always be tenable and not just what could have popped up through a data sampling or modeling error, or random chance, as we’ve frequently discussed here.

These researchers reported the associations as odds ratios and were unable to derive a single valid ratio, but one. The only one large enough to even be noted was a 2 1/2 times higher odds of Tanner stage 3 at grade 5 (age 10 1/2 years) among the African American girls.

This difference has been documented in numerous studies and government reports. For example, a large study of 17,077 girls examined in pediatric offices in North Carolina found that “over 7% of 4 year old black girls showed some sign of pubertal development compared to less than 1% for white girls and by 8 years of age these numbers had risen to almost 50% of black girls and almost 15% for white girls.” In this study, first periods were nearly a year earlier for the black girls. The North Carolina pediatricians noted that their study concurs with other population studies and historical data going back to 1948.

This week’s study added no new information to the body of evidence concerning puberty onset among girls. But it was used to repeat and spread fears about childhood obesity and of puberty occurring in younger girls, based on speculations and poorly conducted studies. For example, their suggestion quoted in the press release that early puberty — and hence, by association “obesity” — leads to behavioral problems, sexual promiscuity, etc. Had anyone examined the evidence for such claims, they would have realized just how uncredible they were. As an example published in a 2005 issue of Prevention of Chronic Diseases, researchers examined survey questionnaires from Israel Defense Force recruits from 1986 to 2000. They reported a trend of decreasing age of first menses among these young women. They also found an increasing trend among teen girls of smoking and using oral contraceptives.

Making the leap that these correlations had something to do with each other makes one of the biggest errors: believing a correlation can ever show causation.

Putting a study into context

There have been countless studies to determine and follow the onset of puberty and explain the trends. The age that girls begin puberty has been decreasing worldwide for decades, if not centuries. Downward trends have been noted in London, Olso, Copenhagen, the Netherlands, and Hungary. Change towards earlier menstruation began around 1920 among Japanese girls, with one study noting the age has dropped about 4 months per decade. The New England Journal of Medicine had reported that American girls in 1890 began their periods at an average age of 14.8 years of age, and according to the National Center for Health Statistics, it had dropped to 12.6 years of age by 1998.

Pediatric endocrinologists reviewed the worldwide evidence in last June’s issue of Indian Pediatrics and explained the findings and inconsistencies reported in the literature. The data has consistently shown, they said, that as food and calorie availability and health improves, and socioeconomic status is enhanced, sexual maturation is spurred. Such favorable factors, however, are unequally distributed:

Even within countries the age of beginning of puberty needs to be assessed separately in urban and rural areas and in well-off and under-privileged conditions, especially in the developing parts of the world such as India. In Western Europe where data for nearly last 200 years is available, the age of menarche can be observed to have decreased from 17 years to 12.8 years... there is a general observation that age of menarche is late, around 15-16 years in rural girls who are relatively thinner and undernourished.

In countries such as China and Senegal from where large data is available, the mean age of menarche in rural areas is still as high as 16.1 years. Taken together these data highlight the crucial role of socio-economic and nutritional conditions on the timing of puberty. There also seems to be a negative impact of early involvement in intense physical activity and energy expenditure on the timing of puberty.

As stated earlier the age of menarche has been shown to have reduced from the 19th to 21st century...This secular trend of progressive reduction in the age of menarche was very pronounced in US and Western Europe from 1960 to the 1990s. Recently however, the secular trend towards earlier menarche in US and Western Europe seems to have halted. There is a north to south gradient in the age of menarche with girls in the southern parts achieving an earlier menarche suggesting the influence of climatic conditions. It has also been shown that more girls attain menarche in winter than summer suggesting inhibitory effect of photo stimulation on puberty....[and] intense psychological stress such as at the time of war is known to delay the onset of menarche significantly.

They cautioned it was important to differentiate normal early development from an abnormality, a condition called “precocious puberty.” Precocious puberty and the serious pathologies associated with it, such as congenital anomalies, brain injuries and tumors, are separate from the normal variations in development among children. But because of the general population trends of younger ages for the onset of puberty, diagnosing precocious puberty has become more difficult and the definition itself has been evolving. But it can be easy for consumers or untrained reporters to mistake the conditions and needlessly heighten concerns about early puberty.

Even the appearance of puberty changes, such as breast growth, in younger girls is also commonly misunderstood. It often doesn’t not mean the onset of real puberty, nor does it affect the progression of puberty and age of menstruation. Researchers examining National Health Examination Surveys from 1963 to 1970; Pediatric Research in Office Settings data from 1992-1993; and National Health and Nutritional Examination Survey (NHANES III) from 1988 to 1994 found that even when onset of breast development was earlier, the age of menarche was unchanged. The age those same girls achieved full breast development was also no different. In the June 2001 issue of Pediatrics, these researchers concluded:

Thus, although these data suggest that puberty is beginning earlier than previously thought, it is not being completed earlier nor is menarche occurring earlier. Puberty among those with early onset may be progressing at a slower pace, or the initial appearance of breast growth may not herald the real onset of puberty. The earlier onset may be attributable to a different ethnic mix or a shift within minority groups, influencing the overall data.

The impact on the diagnosis of precocious puberty involves the requirement of criteria more than a simple age limit. All puberty that appears to begin with breast development when a girl is age 6 or 7 is not precocious puberty. Only puberty that progresses inappropriately so that growth and developmental characteristics are clearly excessive for age with diminished growth potential should be considered for therapy to suppress pubertal development.

Earlier puberty also doesn’t mean that a woman’s fertility period, and her hormonal exposure, is longer, as is often feared. The data has shown that early menarche is associated with early onset of menopause, and late menarche with late menopause.

While this week’s study looked just at girls born in 1991, most researchers realize that looking at the bigger picture and a longer time horizon is necessary before making conclusions about possible trends. A study looking at the effects of the magnitude and velocity of BMI on the age of menarche using Fels Longitudinal Study data of girls born from 1929 to 1983 found that higher BMIs did not cause early menarche. Instead, these researchers from Wright State University School of Medicine in Dayton, Ohio, found that significantly higher BMIs appeared after menstruation began. They found that the mean age of menarche has been stable since 1965 and that BMI trends are a separate phenoma. They concluded:

[G]irls with early menarche were found to have no greater BMI than average- and late-maturing girls until after menarche had occurred. In addition, whereas BMI and BMI velocity increased during perimenarche in girls born after 1965 compared with girls born 1929–1964, this upward shift in pubertal BMI was not accompanied by an acceleration in the pace of maturation, measured by either the timing of menarche or the timing of linear growth landmarks. Our results counter the concern that national increases in childhood adiposity necessarily lead to earlier menarche in girls and furthermore demonstrate the utility of long-term serial data for elucidating the temporal relations between body composition, growth, and development in US adolescent girls.

Will we repeat history?

During the Victorian era, doctors placed enormous significance on menarche, according to Dr. Joan Jacobes Brumberg, a Stephen H. Weiss professor at Cornell University and author of The Body Project: An Intimate History of American Girls.

“If a girl’s reproductive life did not start correctly,” she wrote, “it was believed that she was doomed to ill health and debility. Therefore, the age at which menarche occurred began to assume a great deal of importance.”

Early medical literature sought to answer why some girls menstruate before others and what was the ideal age. Theories abounded, said Dr. Brumberg, claiming city girls entered puberty before country girls, brunettes before blondes, etc.

And many subscribed to the view that both ‘Negro’ girls and ‘Jewesses’ menstrated early because they hailed originally from warm climes where secuality was likely to be more primative and precocious. (White southern belles in the United States were somehow excluded from this formulation.)

In the Victorian mind, age at menarche came to be regarded as a marker of the moral quality of a civilization rather than as a sign of economic conditions. Instead of viewing lowered age as an outgrowth of material well-being, as we know it to be, nineteenth-century Americans developed a very different idea: the lower the age, the more libidinous or sexually licentious the society, nation or race...Fearful of what early menarche symbolized, some parents and even doctors tried to stop the process by restricting a girl’s intake of foods that were considered secually ‘stimulation,’ such as cloves, pickles and meat.

The attitudes, prejudices and fears are eerily similar to those heard in the news this week. For the health and well-being of our girls, let’s hope we’ve moved beyond the medical practices and beliefs of the Victorian Era.

© 2007 Sandy Szwarc. All rights reserved.

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