Two groups of children, both of Han Chinese descent, showed no significant differences in their birth methods, breastfeeding history, or antibiotic use during infancy. There was only one major difference: one group grew up in Perth, Australia, while the other grew up in Hebi, Henan Province, China.
The results were far from similar. Children who grew up in Australia experienced atopy, food allergies, and wheezing much more frequently than their distant cousins who grew up in China.
The findings came from a study led by Jing Guo and her team, published in the World Allergy Organization Journal in August 2019. The study examined 58 Chinese-Australian children aged 3 to 18 in Perth and 63 Chinese children aged 2 to 17 in Hebi.
All children underwent skin prick tests to assess atopy status. They also completed questionnaires on food allergies and wheezing, and provided throat and stool samples for microbial analysis.
A Striking Gap in the Numbers
The differences were substantial. Atopy was recorded in 62.1 percent of Chinese-Australian children, compared with just 12.7 percent of Chinese children, nearly a fivefold difference. For food allergies, the figures were 25.9 percent versus 7.9 percent.
For wheezing, they were 27.6 percent versus 3.2 percent, more than eight times higher. All three differences were statistically highly significant.
Because the two groups shared the same genetic ancestry and did not differ in classic risk factors such as birth method or early antibiotic use, the researchers turned their attention to one clearly different variable: the composition of microbes in their bodies.
Microbes That Changed After Moving Across Continents
Throat and stool samples from the Australian children showed lower bacterial community diversity than those from the children in China, as measured by the Chao1 index, which estimates the number of different bacterial types. Meanwhile, the Shannon index, which measures how evenly the proportions of different bacterial types are distributed, was higher among the Australian children.
In other words, the Australian children's microbiomes contained fewer types of bacteria, but their proportions were more evenly distributed. According to the researchers, this pattern reflected the influence of Western environments and lifestyles.
Their bacterial composition also differed. At the phylum level, the stool samples of the Australian children were dominated by Firmicutes (49.4 percent), while those of the Chinese children were dominated by Bacteroidetes (47.5 percent).
Bacteria That Move Alongside Allergies
The researchers also examined whether the altered bacterial patterns found in the Australian children consistently appeared in children who actually had allergies, regardless of their country of origin.
In the throat samples, the results were highly consistent: 84 percent of the bacterial types that changed in the Australian children also changed in the same direction among children with food allergies. The pattern in the stool samples was much weaker, with only around 24 to 30 percent of taxa showing consistent changes.
The researchers concluded that Western environments and lifestyles shape a human microbiome profile that differs from those found in the Asian environments studied. These differences may also contribute to the higher prevalence of asthma and allergies that has long been recorded in industrialized countries.
Because the study compared children with nearly identical genetic backgrounds, the findings strengthen the conclusion that the gap in allergy rates is linked to the environment in which the body develops, rather than heredity.
