CHICAGO - Call her the Incredible Shrinking African American Woman.
In an age when the adult populations of most industrialized nations have grown significantly taller, the average height of black women in the United States has been receding, beginning with those born in the late 1960s.
The difference in stature between white women and black women has now stretched to three-quarters of an inch and appears to be increasing, according to newly released data from the National Health and Nutrition Examination Survey (NHANES).
The main culprit appears to be diet.
The average height of a black woman born in the 1980s is just under 5 feet 4 inches; her mother, born in the 1960s, is more than half an inch taller. Even her grandmother, born in the 1940s, is a bit taller. The average white woman born in the 1980s is about half an inch taller than her mother.
The gap is "truly phenomenal," according to John Komlos, an economist and historian who has made a specialty of studying human heights. "Such a steep decline is practically unprecedented in modern U.S. history."
You have to go back to the antebellum South to find a similar shrinkage. The generation of white men born in the 1840s who experienced the ravages of the Civil War lost nearly an inch to their Northern counterparts, Komlos says.
A Chicago native who is a professor at the University of Munich, Komlos made a name for himself several years ago when his research revealed that the average height of adult Americans, once the tallest to roam the planet, had stopped rising after World War II and has since been surpassed by that of several European nations. The Dutch now lay claim to the title of tallest.
Komlos' latest findings, based on the national survey conducted by the Centers for Disease Control and Prevention, suggest that after nearly 25 years of stagnation, the average height of adult Americans born from 1975 to 1986 has edged up again - with the exception of black women, whose height is moving in the opposite direction.
The reason this matters, according to Komlos, is because "height is a very good overall indicator of how well the human organism thrives in its socioeconomic environment."
His argument is bolstered by another discovery: While the heights of low- and middle-income black women are plummeting,
-income black women are growing taller and rapidly closing the gap with their white counterparts.
An individual's height is fixed mainly by genes, but the average height of different categories of people is determined to a large extent by external factors.
Komlos, who has been studying heights since the early 1980s, says the downward trend among black women was "quite unexpected."
"There have been declines before" in the U.S. population, he says. "But never this quickly."
Nancy Adler, director of the MacArthur Foundation's Research Network on Socioeconomic Status and Health, says Komlos' latest findings were "puzzling" but consistent with what is already known about the impact of income disparity, access to health care, and educational levels on a person's overall well-being.
Also baffling, Adler says, is the disparity between black men and black women, "since they are subject to the same pre-birth conditions" and then grow up in the same environment.
"The only reasonable explanation we can come up with is diet and the obesity epidemic among [middle- and low-income] black women," Komlos says.
Over the last three decades, the prevalence of obesity among white Americans has tripled, while among blacks it has increased fivefold.
Black females were hardest hit: Almost 80 percent of black females are overweight or obese, compared with 62 percent of the total female population, the CDC says.
The problem develops early. Twenty-one percent of black females ages 2 to 19 are overweight or obese, compared with 12 percent of white girls.
Another oddity, according to Komlos, is that black children, both male and female, grow faster and taller than their white counterparts in early childhood, but whites catch up and pass them during the teen years.
Pediatric growth experts offer one possible explanation. High caloric intake from an unhealthy diet fuels an early growth spurt among black children, plus it speeds the onset of puberty, especially for black girls, who now begin menstruating 81/2 months ahead of white girls. This early onset of puberty reduces the duration of the critical pre-adolescent growth spurt, resulting in a lower adult height.
Komlos blames the long stagnation of American growth rates that began in the 1950s and the current obesity epidemic on the one-two punch of television and fast food.
"In my opinion, the pressure to consume is so high on the American population that it is very difficult for anyone to withstand the urge," he says. "Education and income help, but the pressure is pretty overwhelming."