SDOH-Induced Changes to Gut Microbiome Could Contribute to Racial Disparities in T2D

New research published today in PLoS One suggests that the gut microbiome may play a role when it comes to racial disparities in insulin resistance and type 2 diabetes (T2D) rates. Findings also indicate that social and environmental factors can account for the gut microbiome differences seen.

T2D prevalence among Black individuals is nearly twice that in White individuals, and it is projected that almost half of Black women in the United State will develop diabetes, authors explained.

“This risk is greater in Black women than Black men and other race/ethnicities, in part due to Black women having a high prevalence of overweight and obesity,” they added. Although obesity does promote insulin resistance, the mechanisms contributing to the progression of insulin resistance in Black women are not well understood, as even in body mass index (BMI)–matched studies Black women exhibited greater insulin resistance compared with White women.

In an effort to integrate social determinants of health (SDOH) and physiological outcomes to study insulin resistance in Black women, researchers decided to assess the role of the gut microbiome in the pathway of cardiometabolic disease development.

“The gut microbiome is influenced largely by environmental and social factors, such as diet and psychological stress, and is linked to the development of insulin resistance and T2D,” they wrote.

To carry out the investigation, researchers collected fecal samples from Black (n = 94) and White (n = 74) women enrolled in the National Growth and Health Study (NGHS). Women from California, Ohio, and Washington, DC, between ages 37 and 43 years were included in the current analysis.

Researchers measured participants’ fasting glucose and insulin concentrations via the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR); stool samples were collected between March and September 2019.

Overall, 46% of Black women were classified as insulin resistant compared with 30% of White women; fecal assessments showed that diversity within a sample, or alpha diversity, did not differ by race nor by race and insulin sensitivity status.

Additional analyses revealed:

• Diversity within populations, or beta diversity, at the family level was significantly different by race (P = .033) and by the combination of race plus insulin sensitivity (P = .038).
• Black women, regardless of insulin sensitivity, had a greater relative abundance of the phylum Actinobacteria (P = .003) compared with White women.
• There was an interaction between race and insulin sensitivity for Verrucomicrobia (P = .008), where among those with insulin resistance, Black women had 4-fold higher abundance than White women.
• At the family level, significant interactions between race and insulin sensitivity for Lachnospiraceae (P = .007) and Clostridiales Family XIII (P = .01) were observed.

Some evidence has shown that greater Actinobacteria characterizes obesity in Black and White adults. However, because in the current study adjustments for BMI did not affect observed differences by race and insulin sensitivity, other factors including inflammation, diet, psychosocial factors, and discrimination could have affected the findings, researchers hypothesized.

Thus far, “only one study has examined social factors as they relate to race differences in the microbiome and found that in young, healthy, Black women Bifidobacterium [the predominant genus under the Actinobacteria phylum] was positively associated with psychological stress,” they wrote, adding this finding “deserves further examination.”

Greater HOMA-IR scores observed in Black women in the current analysis were likely associated with inflammation, authors noted, while “the greater relative abundance of Actinobacteria in Black women in our study may be promoting inflammation and insulin resistance in this group.”

More research is also warranted on the potential roles of Lachnospiraceae and Clostridiales Family XIII in the development of insulin resistance in the populations studied.

Emphasizing that race is a social construct, researchers stressed “we should not be remiss in noting that profiling gut bacteria by race and ethnicity should not be interpreted as a reflection of genetic ancesteral or inherent differences....Thus, our findings that gut bacteria differ in Black and White women highlights the potential impact of social determinants of health on gut bacteria.”

Future studies on these differences should include assessments of social, environmental and behavioral factors, as well as examinations of proinflammatory markers, all of which have been shown to impact the gut microbiome.

Because samples were only taken at one time point, longitudinal analyses were not possible, marking a limitation to the study. More sensitive oral glucose tolerance tests should also be considered in future studies to help investigators better understand the potential link between race differences in glucose regulation and gut bacteria.

Researchers were also unable to adjust for diet, psychological stress, geographical location, and other factors in the current study. Such measurements could link racial/ethnic and cultural differences to environmental factors driving differences in microbial communities, they said.

“A follow-up longitudinal investigation is needed in order to better understand the significance of these findings with the inclusion of social determinants of health as potential mediators,” authors concluded.

“It is possible that social and environmental factors associated with Black race contribute to a unique microbiota profile, that in turn contributes to inflammation and insulin resistance, independent of obesity.”

Reference

Price CA, Jospin G, Brownell K, Eisen JA, Laraia B and Epel ES. Differences in gut microbiome by insulin sensiticity status in Black and White women of the national growth and health study (NGHS): a pilot study. PLoS One. Published online January 19, 2022. doi:10.1371/journal.pone.0259889