Five years ago, we shared statistics about blood type distribution within the MEBO community, based on data from our microbiome study (highlighted here, alongside the diet survey). The results revealed that individuals with type O blood were significantly overrepresented, while type A blood was underrepresented compared to the general population. Additionally, the study found a higher prevalence of Rh-negative blood types within the community.

This week, a member of the MEBO PATM/TMAU Facebook group conducted an ad hoc poll about blood group types. The poll received 30 responses, where participants shared their blood types and Rhesus factors. The pie charts accompanying this post illustrate the responses, which reflect a similar pattern to our findings from five years ago. Once again, we observe an overrepresentation of O and Rh-negative blood types and underrepresentation of A.

Globally, Rh-negative blood types are relatively rare. Approximately 16% of the population in Europe and 15% in the United States are Rh-negative. The prevalence is even lower in other regions, such as sub-Saharan Africa (1-3%), Nigeria (6%), and countries like China, Japan, and Korea, where less than 1% of the population is Rh-negative. These contrasts underscore the unique distribution patterns observed within the MEBO community.

Group O is relatively overrepresented in the US general population but still constitutes less than 50% of population, while A constitutes about 40%. No country's general population matches the distribution of blood types in MEBO community. 

However, it is important to acknowledge the limitations of the recent poll. The potential for selection bias or response bias exists due to the nature of the poll and the audience it attracted. For example:

• Self-selection bias: Individuals with type O blood may feel more inclined to participate because they perceive the question as directly relevant to them.

• Confirmation bias: The person conducting the poll might unintentionally highlight responses that align with their own blood type.

• Community bias: The MEBO group may naturally include more individuals with type O blood due to the relevance of this blood type to specific conditions of interest.

Despite these limitations, we note that the analysis from five years ago was less subject to such biases. The main bias in the earlier study stemmed from the population’s shared interest in microbiome research and their awareness of their own blood types. Interestingly, many individuals at the time were not aware of their blood type, which reduced the likelihood of response bias.

While the Facebook poll results may be skewed due to the method of data collection, cross-validation with our previous study lends support to the observed patterns. This reinforces the reliability of our inferences regarding the blood type distribution within the MEBO community. 

Recently, a PATM sufferer from our community shared his hypothesis that agglutinogens can "bind" or interact with volatile compounds, similar to how certain molecules can interact with odorants. Agglutinogens are antigens (molecules that can trigger an immune response) found on the surface of red blood cells. The most well-known are the ABO and Rh antigens.

The ABO system is based on the presence or absence of A and B antigens. People can be:

Type A: Have A antigens

Type B: Have B antigens

Type AB: Have both A and B antigens

Type O: Have neither A nor B antigens

The Rh system is based on the presence or absence of the Rh antigen (also known as the D antigen). People are either Rh-positive (have the D antigen) or Rh-negative (do not have the D antigen).

The relationship between olfactory processes and blood types (and Rh factors) might be indirect but stems from the following ideas. Blood type antigens (A, B, AB, O) are glycoproteins or glycolipids, which are surface molecules that interact with other molecules. In a similar way, odorant binding proteins (OBPs) and mucus components in the olfactory system are proteins or glycoproteins that interact with odor molecules. Some studies suggest that genetic variations in blood group antigens might correlate with differences in odor perception or sensitivity. For instance, certain blood types might be associated with varying levels of glycoproteins or mucus composition, which could affect odor molecule binding and transport. The Rhesus factor (Rh) is another antigen on red blood cells and can influence immune responses.

Association between odor and blood types is likely due to other variations in our genetics responsible for attracting certain types of gut and skin microbes. For example, the ABCC11 gene, which is associated with blood type, has been linked to underarm odor production. The A allele (dry earwax, less body odor) is far more common in East Asia associated with highest frequences of B group and lowest frequences of negative rhesus, while the G allele (wet earwax, stronger body odor) is more common in other populations (such as European and African). 

Other gene variants predisposing to odors are over and underrepresented in people with other blood types. 

We will continue to explore these intriguing patterns as part of our ongoing research.

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