Dec. 30, 2008 — -- An economist in Germany has noticed a curious trend among Americans: For the past 50 years, black women have been shrinking with each new generation.
Young black women today are nearly an inch shorter than white women their age and about half an inch shorter than black women born in the late 60s, according to an analysis of CDC data by John Komlos, a professor of economics at the University of Munich in Germany.
Heights by gender, class and race in Komlos' study rise and drop in waves over the years, but on the whole, every other group besides black women has remained the same height or gotten taller than their parents since the 60s.
Public health experts can't say exactly what's behind the reduced height, but medical anthropologists, economists and epidemiologists agree that whatever the cause is, it's important.
"A measure of height takes into a number of aspects that money alone doesn't measure," Komlos said. "It's sort of an overall indicator of well-being."
"Height basically tracks your health ... it's all a big combination. It's everything," said Sharon Williams, a biological anthropologist and assistant professor at Purdue University in West Lafayette, Ind.
Genes play a big role, but nutrition, activity and the number of illnesses can all influence a person's final height. A malnourished child will have stunted growth, but higher body fat in girls leads to earlier puberty, which draws the time for a child to grow taller to a close.
"Add on top of that, psychological health and psychosocial health," Williams said.
The psychological impact can take time to build. First, a person may become stressed for a period of time, which biologically weakens their immune system. The person may then catch more colds and illnesses, and over a period of a childhood and adolescence, their bodies spend more time fighting disease than growing.
"Height is a really good indicator that anthropologists and social scientists and also the medical community use," Williams said.
Height Difference Between Races
Williams has seen evidence of a height gap among black women in her own work, but Komlos' large analysis only left her with more questions than answers.
"It doesn't give us any of the really interesting information about why," said Williams, who noted it's a wide net to divide all of America, with so many different cultures and lifestyles, into two racial groups.
"This is a statistical study that really misses out on what's going on. ... It's what we do now, but it isn't the best thing," she said. "What's more interesting to me is what's going on in a small scale, in small communities."
Searching for answers about Americans' height can get even more complicated, depending on which study you choose.
A study released in October by the National Health and Nutrition Examination Survey (NHANES) compared heights of black women across 10-year age periods, instead of five, as Komlos does. That study didn't show a height difference across young adult and middle-aged black women.
"They look the same, the mean is identical," said Cynthia Ogden, an epidemiologist at NHANES in Washington, D.C.
According to Ogden, how frequently the government took surveys, how the government defined race, and which ages the government chose to include has changed periodically since the 1970s.
"So, I think it's very hard for me to give an easy answer about anything," Ogden said.
Such changes were precisely why Komlos said he compared and contrasted the NHANES numbers. He had noticed the beginnings of this trend in past research, and only found enough data to show a shrinking stature among black women in the October study.
"They (the CDC) collect millions of data on different kinds of information from blood pressure to whatever have you," Komlos said. "Height is not something that is of particular interest to them, it seems to me."
However, even Komlos thinks there is more research and analysis to be done to determine what the height disparity found in his study might mean.
For example, why the height decline, the study found, is mostly among the lower and middle income group.
Race Only Part of the Picture
Ellen Gruenbaum, a professor and head of the anthropology department at Purdue University, was also curious about how income levels shaped Komlos' findings.
"Statistics kept by imprecise categories like 'race' often reflect what are really socioeconomic and lifestyle differences," she said. Height, health and socioeconomic status are definitely connected, she added.
Considering that black men have grown taller in recent generations, and now measure an average of a third of an inch shorter than white men, according to Komlos' study, Gruenbaum hopes researchers follow up with studies about earlier puberty for girls and neighborhoods that promote or do not promote exercise.
"Higher socioeconomic classes generally have safer environments, better schools, more parks and safer streets for play, exercise, walking to school, etc," Gruenbaum said in an e-mail to ABCNews.com. "Dangerous neighborhoods, by contrast, lead to children -- especially girls, perhaps -- staying inside more for safety."