A couple of days ago I was having a conversation with some friends of mine. For some reason I can’t fully remember, we got to talking about Sexually Transmitted Diseases (STDs). Much of the discussion centered around the fact that STDs such as chlamydia are extremely common nowadays. Not just in developing nations, but also in developed ones.
The natural question that follows from this recognition is: Why is the modern man – and woman – so prone to develop STDs?
Fitness criteria are fluid
Why do some people get very sick if they drink water that contains moderate-high levels of pathogenic microbes, whereas others only experience mild gastrointestinal discomforts following such a behavior? Why are sick, hospitalized patients at much higher risk of becoming infected with Clostridium difficile than healthy, non-hospitalized people? Why do some women frequently develop vaginal yeast infections whereas others never experience any issues in that department? Why are some people more prone to develop STDs than others?
In order to answer these questions, we need to take a step back and look at how organisms interact with their environment.
All organisms on this planet are a product of evolution. Over evolutionary time, different organisms have adapted to different environments. Whereas tigers do their best work in hot, savanna-like habitats, polar bears prefer to live under cold, arctic conditions. Just like animals, microbes also differ with respect to their environmental preferences. Some bacteria, such as Lactobacillus plantarum, the dominant type of bacteria in fermented foods such as sauerkraut, thrive under very acidic conditions, whereas others are incapable of surviving in low pH environments.
This leads us over to the questions posed earlier. One of the main reasons why some people are more prone to get sick following exposure to pathogens such as C. diff, Chlamydia trachomatis, and HIV than others is that fitness criteria are fluid. An organism that does well in one environment doesn’t necessarily do so well in another milieu.
It’s important to remember that from the perspective of the microbes that colonize your skin, gut, mouth, and so on, your body is an environment. If you suddenly decide to change your diet, adopt a new exercise routine, or otherwise alter your lifestyle in a major way, the environment that is your body will change. Consequently, your microbiota will also change. Those organisms that did well under the past environmental conditions don’t necessarily thrive under the new conditions. This is not only true for microbes that are already present on your body, but also for bacteria, fungi, viruses, and other tiny life forms that you could potentially be exposed to via activities such as eating, kissing, and sex.
This can largely help explain why some people are a lot more prone to develop STDs than others. Someone who harbors a resilient, diverse microbiota is better protected against microbial invaders than someone who’s colonized by an imbalanced, unstable microbial ecosystem. For example, a woman whose vagina is teeming with Lactobacillus bacteria that spew out a lot of lactic acid is much less likely to develop a yeast infection than a woman whose reproductive tract has a high pH and isn’t dominated by lactic acid-producing organisms. The former will also be less susceptible to develop many, if not all, STDs than the former. Not just because the friendly bacteria that live in her reproductive tract produce a variety of compounds that are toxic to many pathogens, but also because they stimulate her immune system in such a way that nasty, STD-causing bugs have a hard time setting up shop in her body.
These statements are supported by recent research, including studies showing that friendly bacteria such as Lactobacillus crispatus, L. gasseri, and L. jensenii can destroy pathogens such as Chlamydia trachomatis and that a woman’s risk of becoming infected with HIV is partly determined by the state of her vaginal microbiota (1, 2, 3, 4). It’s somewhat trickier to study the microbiota associated with the male reproductive system than the one associated with the female reproductive system; hence, most studies in this area have focused on the microbes that colonize females. With that said, there’s no doubt in my mind that the things we’ve talked about so far not just apply to women, but also to men.
Perhaps needless to say, the state of your microbiota is not the only thing that determines your risk of developing STDs. The first and most important thing one can do to lower one’s risk of picking up a STD is obviously to be careful about who one decides to jump into bed with. Moreover, if one does decide to jump into bed with a partner one doesn’t know that much about, it’s obviously wise to consider using some kind of protection.
What can we do to ensure that the microbes “downstairs” work with us, not against us?
Over the past two decades, numerous studies have examined the composition and workings of the human gastrointestinal microbiota. Less attention has been devoted to the microbes that are associated with the human reproductive system, particularly those associated with the male reproductive system. This is not to say that we don’t know anything about the critters that live “downstairs” though. We do know quite a bit about them. With that said, our understanding of what it takes to build a healthy, species-appropriate gut microbiota is much better than our understanding of what shapes the microbiota associated with the human reproductive system.
Some researchers have experimented with vaginal microbiota transplantation (yes, such a thing actually exists. Perhaps someday it will be a common procedure), and if you do a quick search on Google, you can find several online stores selling vaginal probiotics. Is this where the key to a healthy vaginal microbiota lies? No… In some instances, a microbiota transplant or the use of probiotics may perhaps be warranted; however, with that said, I think it’s a mistake to think that one can build a healthy microbiota simply by taking some probiotic capsules – or putting them into one’s reproductive tract – or performing a microbiota transplant.
The reason why I hold this belief is simple: One can’t simply infuse a bunch of microbes into an environment and expect them to set up shop in that environment. This is particularly true if the environment in question is already home to many different microbes that have been living there for quite a while. Those resident microbes may hinder the new ones from gaining access to the resources or ecological niches they need to survive, for example by producing various compounds that are toxic to the newcomers.
The key thing to remember is that the number of microbes that one can infuse into for example the female vaginal tract via a probiotic capsule or a microbiota transplant is typically small in comparison to the number of microbes that are already present in the vagina. Not only that, but one shouldn’t assume that the microbes that are infused are adapted to the environment they enter.
This comes back to what we talked about earlier: Different microbes are adapted to live under different conditions. A female whose reproductive tract is dominated by unfriendly bacteria and has a high pH won’t be able to reconfigure her entire vaginal microbiota simply by infusing some Lactobacilli into her downstairs compartment.
In today’s article, I don’t plan to get into a lengthy discussion about what one can do to take better care of the microbiota associated with one’s reproductive system. That’s a topic for another day. What I would like to say though is that I strongly believe that the microbiotas that are present in our reproductive tracts are greatly affected by the workings of our bodies, in particular the workings of our guts. The microbiota in your reproductive tract may in many ways reflect the state of your body.
If you harbor a healthy, species-appropriate gut microbiota and adhere to a prudent lifestyle, then chances are your “downstairs microbiota” will be in a good state. The reason is simply: By adhering to a species-appropriate diet and lifestyle and caring for your gut microbiota you work towards providing your body with the type of environment it evolved to need in order to function properly. I strongly suspect that the gut microbiota greatly contributes to shaping the microbiota of the reproductive system.
Besides eating healthy, exercising, and so forth, another thing that we can do to ensure that the environment of our bodies supports the development of a microbiota that matches well with our biology is to limit our use of chemical-laden soaps, lotions, and other topical products, including those that are intended for “downstairs use”.
There’s little doubt that one of the reasons why STDs such as chlamydia are so common nowadays is that a lot of people don’t practice safe sex. Moreover, a lot of people are careless with respects to their choice of sexual partners and/or sleep around a lot. What’s important to note though, is that while these things help explain why STDs such as chlamydia and HIV are spreading like fire in dry grass in some countries, they don’t explain why STDs exist at all or why some people are a lot more prone to develop STDs than others.
It’s not surprising that yeast infections, chlamydia, and other similar conditions are so common nowadays, seeing as few, if any, contemporary humans harbor a truly healthy microbiota. A reproductive tract that is dominated by friendly microbes (e.g., Lactobacilli) possesses a natural defense against pathogens, including those that cause STDs, and is much less likely to be taken over by problematic organisms such as Candida albicans, HIV, and Chlamydia trachomatis than a reproductive tract that has a high pH and is home to a microbiota that doesn’t match well with the human body. In other words, one of the most important things we can do to lower our risk of developing STDs is probably to take better care of the friendly bugs that colonize our bodies, including those that are associated with our reproductive systems.