Past studies have shown that each American generation is taller than the last. But surprisingly, African-American women are getting shorter, says a new study conducted by the National Health and Nutrition Examination Survey (NHANES).

According to the data, on average, African-American women born in the 1980s were a little shorter than 5 feet and 4 inches; those born in the mid-1960s were more than a half an inch taller. John Komlos, the study’s lead author and a professor at the University of Munich in Germany, believes that while genetics play a role in height determination, there is a relationship between obesity and the decline in height.

The National Center for Health Statistics reported in 2007 that 23.8 percent of female African Americans between ages 12 and 19 are overweight, compared with 14.6 percent of their white counterparts.

Past studies have made a correlation between obesity and the early onset of puberty in young people. For young women, the female hormone estrogen causes the ends of long bones to close—and these bones are responsible for growth. When that process is accelerated, it can result in shorter adults.