The germ theory of disease was developed by the French scientist Louis Pasteur in the late 19th century. His idea that invisible bacteria and viruses cause disease is now a cornerstone of Western medicine, as we’ve developed a large array of medicines to fight back against these invaders (that’s why we “pasteurize” milk as heating it kills the germs). Surprisingly, though, on his deathbed, Pasteur renounced his theory in favor of a rival approach — the terrain theory of disease.
In this model, the key feature was not the presence or absence of germs, but the innate health status of the person (what are called “host factors” in modern medicine). In other words, the body was the “terrain,” the internal environment, the soil in which bacterial “seeds” tried to sprout and take root. Not everyone who is exposed to a pathogen gets sick: if the body is healthy, bacteria can’t thrive, but a weakened body can be overwhelmed by invisible invaders.
It’s an important distinction for several reasons. Though neither Pasteur nor his rival, Claude Bernard, knew about immunology, we now realize that the immune system is a key factor in determining health. Bacteria and viruses have always been present in our environment, and over the past several hundred thousand years, humanity has generally been resilient enough to bounce back from other plagues. So what, if anything, is different this time around with the COVID pandemic?
Our public health policy has strongly focused on the germ theory’s approach, aiming to vaccinate all Americans, even beyond the original 70-80% target that would bestow “herd immunity” and cause the virus to wither on the vine. So Americans are encouraged to rely on an external agent to bring them health, without any direction on how they could also improve their “terrain.”
But optimizing “host factors” could make it harder for viral “guests” to enter our bodies through the “open door” of ill health: a healthy immune system can shut that door. And thanks to advances in the field of psychoneuroimmunology (PNI), we know how to do this. So here are several key approaches that boost our own immune resilience, as a complement to what vaccines do. These are cheap, effective and empowering, giving people a sense of influence and agency over their own health.
The first area PNI investigated was the role of stress in impairing immune function. It was a controversial idea when first proposed by Hans Selye in the 1950s, but it’s now widely accepted. So one key step in dealing with COVID — easier said than done — is to learn how to manage stress effectively. That’s a topic worthy of another essay, but everything from meditation to socialization, from walking in the woods to listening to music, can help boost your immunity; it also increases your sense of empowerment and decreases any sense of helplessness.
Several other factors are very specifically related to COVID, and emerged from analyzing the characteristics that COVID-related deaths share. The factor most strongly correlated with poor COVID outcomes is the amount of Vitamin D in the bloodstream. That might seem an odd connection, but Vitamin D is a key booster of the immune system, and its levels tend to be low in Americans in general, perhaps because we spend more time absorbing light from our computer monitors than from the sun, which our bodies use to make Vitamin D; annual winter spikes in colds and flu are related to shorter days with less sunshine. Yet there has been almost no public health messaging about this factor, or even free distribution of this inexpensive vitamin supplement to at-risk populations.
Another risk factor is obesity, which not only impairs pulmonary health but also sets the stage for the over-active inflammatory response that does so much damage to COVID-infected lungs. So where’s the publicity about weight loss to prevent COVID, or infomercials about decreasing our bodies’ chronic low-level inflammation via so-called anti-inflammatory diets?
Exercise is another key preventive factor whose value is not widely known. A recent study showed that, among people who developed COVID symptoms, those who had practiced regular exercise before they became ill had almost three times the chance of avoiding hospitalization, while those who rarely exercised were much more likely to end up in the ICU or to die.
So in summary, I think our approach to COVID should be based on both the germ theory of disease (vaccines, masks, social distancing) and the terrain theory of disease (self-care measures like stress management, Vitamin D supplementation, weight loss, and exercise). In other words, let’s use both models, rather than choosing just one, as the best way to get through this crisis.
Rick Leskowitz, MD, is a retired psychiatrist and Buckland resident who worked for many years in a holistically oriented pain management program at Spaulding Rehabilitation Hospital in Boston.