Raising healthy kids…and their bacteria? (Summer reading, part V)

I’m a biologist, an educator, and a parent. I intentionally consume a lot of new information about science in the course of my work and more casually through social media and the news. I stay informed about many different topics to benefit my students, my family, and my own curiosity. To kick off my summer reading experiment this year, I started with a book about bacteria (I Contain Multitudes, by Ed Yong), which discusses at length how microbiomes (communities of diverse bacteria in and on the human body and the bodies of other animals) influence our lives. What scientists and physicians have learned about the diverse types and lifestyles of bacteria has exploded in recent years but likely is still dwarfed by what we don’t know. We can’t easily observe the habits of bacteria, so we’ve been a little slow to appreciate their contributions. But new methods of investigation, such as DNA analysis, and increased research into this topic are revealing new and exciting moments of discovery and building connections that are refining our understanding of our relationship on planet Earth with our tiny neighbors.

I recently heard about another new book about bacteria called Dirt Is Good: The Advantage of Germs for Your Child’s Developing Immune System, by Jack Gilbert, Ph.D., Rob Knight, Ph.D., with Sandra Blakeslee (journalist). Both scientists are at the forefront of research into the complex relationships humans have with microbial environments (for more information on what they study, see these links to Gilbert’s and Knight’s websites). So, I decided to add it to my summer reading list and see what it added to the conversation about microbes. The book presents an interesting approach to communicating scientific information about bacteria: it’s a parenting resource, presented mostly in conversational form with parents’ questions and experts’ answers relating to different topics about pregnancy and birth, diet and digestion, specific medical conditions, and the home environment–all from a microbiome perspective. For a personal touch, each author provides some anecdotes from their own experiences, which makes for a less clinical take on this topic. (For a summary of a few of the questions and answers, check out this recent review of the book from National Public Radio.)

The fact that a parenting book about human microbial communities has been written at all reflects a recent shift in scientific thinking about bacteria in our domestic lives. After Robert Koch, Louis Pasteur, and others discovered that bacteria are responsible for many potentially serious infectious diseases (see this link about the germ theory for more background), we engaged in a broad mission of biological warfare against invaders that make us sick, with much success (think: antibiotics and disinfectants). We of course have a long way to go toward controlling outbreaks of infectious disease around the world (consider cholera, which continues to infect millions and kill thousands of people each year; see this link for more information) It’s been only recently that we have come back around to appreciating the rich diversity of non-pathogenic (disease-causing) microbes in our midst that have nothing to do with human disease, or, in many cases, are likely benefiting our own bodies’ digestive processes, immune responses, skin health, etc. Essentially, as described by Gilbert and Knight (as well as many other people), we may need to consider the balance of microbes in our ecological habitats–and in our own bodies–for better health. Of particular concern to the authors is how a societal shift in many developed societies toward environments that are perhaps “too clean” may be negatively influencing the health of children. This idea has been dubbed the hygiene hypothesis (read more here), and many scientists are examining questions related to children’s health under different sorts of conditions (urban vs. rural, “sanitized” vs. grubby,  birth method, breastfed or not, etc.) that could influence the types of microbes to which children are exposed.

I was first introduced to the hygiene hypothesis over 15 years ago through a video segment in the landmark PBS Evolution series that profiled the work of German scientist Erika Von Mutuis, an early researcher into how bacterial exposure influences rates of asthma and respiratory allergies, which have spiked more recently in children compared with previous generations. By studying environmental differences in rural vs. urban homes, she proposed that exposure to farm animals and the dust and soils in farming communities likely “trained” children’s immune systems to a wide range of bacteria, making these children less likely to react to other airborne irritants and develop medical problems. In Dirt is Good, Gilbert and Knight expand on this idea by including a wide range of more recent data suggesting that exposure to pets, farms, and outdoor play in the dirt (think: mud pies!) primes developing immune systems to a wide range of natural and harmless bacteria. Much of the book is also devoted to why breastfeeding is thought to promote benefits in digestive system development, why antibiotics should be used sparingly to avoid microbial resistance (but why vaccines are beneficial), and whether probiotics (foods or ingredients that promote beneficial bacteria) or microbiome tests are worth the hype.


Gilbert and Knight discuss that having a dog is a great way to introduce microbes into your family’s life. They’re kind of fun to have around, too! By I, Perhols, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2399580

While reading, in addition to considering the scientific topic, I was thinking about how this book contributes to a broader issue in science: how scientific information makes its way from people doing work in science out to people who are busy with other types of jobs. One of the major problems facing folks who go to some effort to stay abreast of science news, or for those who seek out health or parenting advice in an effort to make the best choices for themselves and their families is: how do you know what information to act on, in a world in which new scientific discoveries seem to keep changing the rules on us? I receive frequent, frustrated questions and comments from students, family, and friends about what to believe, or how it’s sometimes hard to trust science and scientists, because the information keeps shifting (and sometimes changes its mind about what’s good or what’s not!). Is red wine good for you, or bad? How about eggs? What about coffee? How much exercise do you need? In general, how can people who genuinely want to learn more or apply science to their lives find and interpret useful information? Learning to avoid charlatans with misinformation or something to sell is also a challenge. Gilbert and Knight decided to take time out from their investigations into microbiomes and write a parenting guide about bacteria, for an audience of curious or concerned parents who want to be informed about new health findings. This is not something every scientist feels comfortable doing, but a movement is afoot to help more and more scientists summarize their work and communicate it with the public at large. Will everything in Dirt Is Good hold up to be “truth” a generation from now (or even a year from now)? Maybe, maybe not. Probably some of what they discuss will be contradicted down the line. But Gilbert and Knight have the credentials and the experience to present and give some context about the information we have at the moment; new research may solidify, refine, or overturn our best understanding for now, and that’s okay. That’s how science works, in an incremental quest toward appreciating how the natural world is put together. Rather than feel frustrated that I had incomplete, or incorrect information about bacteria and immune development when my own children were babies (did I introduce yogurt or peanuts at the wrong times?), or feel too smug about any perceived successes (Yes, I have pets! I must be an awesome parent!), I can ponder the new information and watch how ongoing efforts by scientists and physicians will ultimately lead us closer to a better understanding, and that future generations may benefit from our ongoing discoveries.

It’s also important to remember when reading a particular source of information about science or health that the topic is summarized to fit the goals of the project (website, column inches, book length, etc.) and may not include every possible contingency that could affect your life. For example, I wished the authors of Dirt Is Good would have addressed one important caveat when encouraging parents to allow their children to put soil in their mouths: some soils, especially in urban areas, can contain high amounts of lead from the accumulation of lead-based gasoline residues and other products used decades ago. Lead exposure, while not associated with bacterial infection, can itself lead to various health problems in children. Increasing awareness about lead contamination and how parents, urban gardeners, and others can use soil safely is another area of ongoing research that may help us have healthier interactions with our environments. (For a nice summary about lead in soil, see this link from Penn State University.) No single resource about science or one scientist’s area of knowledge is necessarily complete. Each contributes in its own way toward expanding our collective understanding of nature, so it’s important to read widely from reputable sources to discover the range of information we have about complicated topics.

Ultimately, living in human societies is a balancing act between avoiding known or suspected risks and incorporating as many beneficial factors as is feasible. This will vary for each family and geographic region and by the resources available to individuals, but with each new piece of information, we’re better able to understand our environments and create healthier communities and public health policies for as many people as we can, to both eradicate serious infectious disease and promote healthy living opportunities around the world.


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