The probiotic market is flooded with useless – and in many instances harmful – products. Instead of turning to that marketplace for microbial solutions in the form of new materials to add to your microbiome, you may be better off exploring the vast pool of microbial life in which we humans bathe.
Like you, the people you encounter as you navigate your life all carry complex microbial communities. Some of these communities are best avoided, as they are disfigured and riddled with pathogens, typically as a result of long-term exposure to drugs, sugary fast food, and/or other evolutionarily novel, microbiota-disrupting agents; however, others are quite healthy and vibrant and may actually do you a lot of good.
‘Health’ is continually transmitted between people via transfer of bacteria, fungi, viruses, and other small life forms. Perhaps the most obvious example of this phenomenon is seen between mothers and their offspring; a bond that involves transmission of bacteria from the former to the latter at all stages of early child development. For example, during breastfeeding, growing infants are infused with billions of microbes that permeate their gastrointestinal cavities, where they play a role in shaping various bodily processes related to immune maturation, digestion, and brain development.
When it comes to the transfer of tiny life forms that takes place in other settings than the one that has to do with mother-child interactions, most of the focus has historically been on perilous transmissions involving movement of influenza viruses, HIV, C. difficile, Pediculus humanus capitis (head lice), and other living entities that are known to be able to cause us discomfort and harm. Much less attention has been placed on potentially beneficial transmissions, which is unfortunate, as such transmissions are integral to life and important in the context of microbiome restoration.
Just like exposure to viruses, fungi, bacteria, or parasites associated with a sick human can make you sick; exposure to small life forms associated with a healthy human can make you healthy. Perhaps needless to say, you won’t become extremely healthy simply from associating with a very healthy person. Other factors, such as genetics, your diet, and so on, obviously matter as well. The point I’m trying to get across is that it’s possible to generate health via microbial transmission.
In cases where both players are healthy and attracted to one another, both are likely to benefit, as both will be exposed to new, potentially beneficial microbes. In other words, the interaction is mutually beneficial. If one of the players is unhealthy, whereas the other is healthy, the outcome is less clear and will depend on a number of factors, including the exact state of the two people’s microbial communities and the nature and duration of the microbial swapping. In cases where the involved parties are both sick, neither is likely to benefit much, and it may even be that one or both are adversely affected by the exchange.
Obviously, the degree to which microbes are transmitted between individuals who are in contact with one another depends on the nature and extent of the interaction. Simply having a healthy friend that you hang out with on occasion is probably not going to do much for your microbiome; unless you and your friend have an unusually intimate relationship that is. The exposure has to be of a more direct nature in order to have a marked impact.
This leads us over to boyfriend-girlfriend relations…
The microbial implications of romance
Microbial swapping is inherent to romantic relationships. One doesn’t have to be a genius to figure out that why that is. Not only do couples frequently live together, and thereby shed and pick up microbes within their household, but they also tend to be in regular physical contact, kissing a lot, having sex, and regularly touching one another. Not all relationships are like this, but many certainly are, particularly early on, when they’re still fresh.
This obviously involves much exchange of microbial life (Just one intimate, 10-second kiss has been shown to transfer more than 80 million bacteria (1). Not all of the organisms that one is exposed to through such contact are going to have a lasting impact on one’s microbial ecosystem. Some won’t make it in the face of harsh competition or will be wiped out by stomach acid; however, others are going to have an influence on the system they’ve just entered, either because they have an acute effect, put down roots, or leave some part of themselves behind, for example by transferring genetic material horizontally. In turn, this may have a beneficial effect on the human host, for example by augmenting digestive or immunomodulatory processes.
Not surprisingly, cohabitation intensifies the microbial swapping game, with studies showing that the microbial and immunological signatures of couples who live together frequently appear to have “converged” (2, 3, 4). The health effects that may accrue as a result of this type of within-couple sharing of microbes haven’t received much attention by the scientific community, in part because it’s difficult to isolate these effects and establish cause-effect relationships. What has been shown though, is that other forms of microbial swapping that takes place within households, such as transfer of bacteria from pets to children, appear effectful in the prevention of inflammation-related disease (5, 6, 7). Furthermore, it’s well established that microbial exposure in general is critical in the context of human health promotion.
Diversity is key in this regard, in the sense that it’s good (and evolutionarily normal) for humans to be exposed to a diversity of microbes, as opposed to a narrow range of critters, and harbor a diverse microbiota, as opposed to an unvaried one. Intimate relations with healthy people get a high score in this respect, as it is involves exposure to a wide range of tiny life forms. It’s certainly likely to be a lot more fruitful in the context of microbiome enhancement than taking a generic probiotic supplement day in and day out.
Given that microbial exposure is so important to health, it’s reasonable to speculate that part of the reason why social isolation has been linked with a number of adverse health outcomes (8, 9) is that it decreases contact with human-associated microbial communities.
The microbial facets of attraction
The fact that microbes are transmitted between humans who are in close contact with one another helps explain why we’re attracted to healthy-looking people, whereas we instinctually try to avoid individuals who show signs of being in poor health or infected by a pathogen (10, 11). It also sheds light on the biological roots of attraction. Darwinian logic dictates that we’re attracted to members of the opposite sex whose genes “suit” our own, in the sense that a mixing of the two genotypes is likely to produce healthy, vibrant offspring that’s capable of surviving and eventually reproducing themselves.
Our microbiotas add a new dimension to this concept. From a Darwinian point of view, it appears likely that part of the reason why we vary with respects to who we are attracted to is that we vary with respects to the microbial complexes that agree with our individual genetic composites, which in their entirety are composed of both our own genotypes and the genes of the microbes, viruses, parasites, and so on we harbor. In other words, the biological reason why you find some people more attractive than others doesn’t necessarily just relate to human genetics; it may also have something to do with the microbes we harbor. This notion is supported by recent research showing that microbes affect the mating preferences of some animals (12, 13, 14, 15).
Microbial health promotion
By now, you’ve probably gathered that from a selfish point of view, it’s much better to have a healthy girlfriend or boyfriend than an unhealthy one, at least in the context of microbiome augmentation. This presents an obstacle though, which is that it’s now the exception rather than the norm for members of Homo sapiens to be in good health. Acne vulgaris, irritable bowel syndrome, heart disease, and a number of other ills are extremely common in many places, particularly in areas of the world where natural environments have given way to skyscrapers and fast food joints. Truly healthy people are like unicorns these days; they’re rare and difficult to find.
Semi-healthy people are still around though. A combination of two such individuals in a physical relationship may actually generate improved health for both individuals via mixing/sharing of microbes. In other words, when combined, two semi-healthy individuals may both start to move away from the semi-healthy crowd, towards the healthy one, particularly if they already have a healthy diet and lifestyle dialed in. As pointed out earlier, this hasn’t been firmly documented in scientific studies; however, in my mind, based on everything I know, I see it as a plausible outcome.
The fact that health may foster health, whereas illness may foster illness, is obviously relevant to public health. In a semi-healthy or healthy population, one would expect people to be connected in a virtuous, dynamic network in which there’s ample transmission of “good” bacteria. In such a network, lovers and family members are grouped together, albeit not detached from the rest of the world. In a sick population, on the other hand, a self-propagating vicious situation may be generated. This idea really isn’t that far-fetched, given what we know about infectious disease. The only novelty is that the focus has been expanded so that it no longer just includes disease, but also vigor and health.
Your health is greatly influenced by the composition of your microbiota. The composition of your microbiota, in turn, is greatly influenced by the microbial communities you’re exposed to throughout your life. This exposure started early on, as you received a special mix of bacteria from your mother, partly through breastfeeding, and continues for the duration of your lifespan, as you regularly come into contact with microbes associated with plants, animals, and objects, as well as other people. In this respect, intimate contact, typical of romantic relationships, is obviously going to be particularly impactful and could potentially have a profound effect on your microbiota and immune system. Hence, it follows that from a microbial point of view, it’s better to have a healthy partner, as he or she would be expected to harbor health-promoting microbial communities, than a sick partner who may be home to many troublesome microbes.