A study led by UC Davis has found significant differences in gut bacteria between black and white women, even after accounting for their insulin sensitivity status.
Independent of body mass index (BMI), insulin resistance tends to be more widespread in black women than in white women. This contributes to disproportionately higher type 2 diabetes in this population compared to that in white women. It’s still unknown why this is the case.
The study was led by Candice Price, assistant adjunct professor and cardiometabolic researcher at the Department of Molecular Biosciences in the UC Davis School of Veterinary Medicine and the lead author on the study.
“We investigated whether gut microbiome profiles differ between black and white women and if so, do these race differences persist when accounting for insulin sensitivity status. No other studies have analysed the gut microbiome based on insulin sensitivity by race and sex. By characterizing the gut microbiome in Black women, researchers might understand the health disparities in the development of heart and metabolic diseases in this population,” said Price.
The researchers measured the relative abundance of bacteria in stool samples collected from 94 black and 74 white women in the National Growth and Health Study. They analysed the samples and compared the findings based on the participants’ self-identified race and insulin sensitivity status (NB. insulin sensitive versus insulin resistant).
The study found that the BMI and fasting insulin were significantly greater in black women than in white women. For this reason, they adjusted all analyses to account for obesity differences. The study further found that the gut microbiome differ by race and insulin sensitivity status. This suggested intestinal bacteria may play a role in the development of insulin-resistance in women, based on their race and ethnicity.
Almost half of the black women in the study were classified as insulin resistant, compared to 30% of the white women. Insulin sensitivity was significantly lower in black women.
The two most present bacterial types were Firmicutes and Bacteroidetes. They made up around 90% of the total bacteria in all the samples. The study found no differences by race in the relative abundance of these bacterial types, nor in the Firmicutes/Bacteriodetes ratio.
However, black women, regardless of their insulin sensitivity, had a greater relative abundance of another species, Actinobacteria, compared to white women. Actinobacteria are associated with reduced insulin sensitivity and elevated inflammation.
“An important finding in our study is the significantly greater relative abundance of Actinobacteria in black women. Insulin resistance may be prevalent in Black women in part due to this unfavourable high abundance of this bacteria,” said Price.
The study also found significant interactions between race and insulin sensitivity for some other bacterium types, such as Lachnospiraceae and Clostridiales Family XIII. In insulin-sensitive women, black women had twice the relative abundance of Clostridiales Family XIII compared to white women. Among participants with insulin resistance, black women had four times as much Verrucomicrobia than white women.
“Our findings raise the possibility that the gut microbiome could play an important role in driving cardiometabolic health disparities of black women, indicating an influence of social and environmental factors on the gut microbiome,” Price said.
The researchers indicated that race and ethnic differences in the gut microbiome are likely a reflection of environmental influences such as diet, rather than genetics.