A rambling essay on making connections from tobacco leaves.
But first, COVID:
As the plane landed last Monday at the end of a short but celebratory trip to Mexico with my best friends, I noted a bit of a scratchy tickle at the bottom of my throat, right where your neck meets your sternum between your collarbones. By the next morning, it was clear I had brought back COVID. I immediately went into isolation in our guest room, noting that I have the privilege of having a guest room in which to isolate. But it was already too late, and 48 hours later my spouse noted the same exact tickle. We’ve spent 2 years making sure we wear masks, wash our hands, avoid crowded and un-masked places, and we’ve gotten vaxxed, and vaxxed some more. I took a calculated risk going to Mexico, not because it was Mexico, but because it was travel that was non-essential. We all calculated the risks, those of us who went, and those of us who were staying behind, and collectively, after 2 years of putting off, and avoiding, and delaying, and postponing, we went, noting that Omicron numbers were on the decline.
So it goes. Those of us who contracted COVID due to this trip are fortunate to be vaccinated and to be recovering already. Thanks to the predilection of teenagers to not want to be close in proximity to their parents, my girls remain negative. I will be back in the clinic just as soon as my rapid antigen test becomes negative again, or after 10 days go by, whichever happens first. In the meantime, I am working from home isolation.
Why does the tobacco plant produce nicotine? What purpose does it serve the plant to expend energy creating that molecule in abundance? Having humans cultivate and harvest its leaves does not benefit the plant in any evolutionary sense. And getting mammals addicted to tobacco leaves does not help spread the Nicotinia’s genes in the way it would if the addictive substance were, say, in a plant’s fruit (eat the fruit, disperse the seeds as a by-product).
Nicotine is a neurotoxin for insects. So it serves not as an enticement for humans to harvest the leaves and thus grow more tobacco plants, but rather a basic defense against being eaten by insects. Tobacco is part of the nightshade family and all nightshades make some quantity of nicotinic compounds in their leaves, but other members of the nightshade family also create mammal-toxic compounds as well, which is why we are not smoking eggplant leaves.
Humans in particular have a large abundance of receptors for nicotine (nicotinic receptors) in the brain, and these receptors in turn wind up releasing numerous neurotransmitters that are responsible for positive or pleasurable sensations, such as dopamine, serotonin, norepinephrine (happiness, reward, focus, alertness), GABA (decreased anxiety), and acetylcholine and glutamate (focus and alertness, memory, and even coordination). This begs the question of why? What was the evolutionary source that bound to the nicotinic receptor? Surely we did not co-evolve with tobacco. Although it is named the nicotinic receptor, the main target for this receptor is acetylcholine, which is ubiquitous in the human brain. Nicotine just binds that receptor with more affinity and releases more neurotransmitters, which explains why it’s so potent in its effects, and why it’s so addictive.
I read a long essay this week by Dorothy Wickendenon on Wendell Berry, the romantic agrarian philosopher and writer. Berry spent many hours in his formative years harvesting tobacco leaves in the Kentucky river valley where his family and neighbors grew the cash crop, although he never appears to have become a regular user of tobacco himself. As a crop, it grows in thin, poor-quality soil, and can provide a relatively high amount of income for a family with a relatively small amount of land. It also encourages community at the time of harvest, because harvesting tobacco leaves takes the skill of many hands, and is difficult to mechanize.
In the past 20 years, tobacco farming has largely been outsourced to other countries where the land and the labor are cheaper. It is then imported back into the US for consumption, where it produces not only euphoric amounts of neurotransmitters, but encourages the growth of cancerous cells, leads to heart disease, and makes brittle our lung tissue.
Nicotine by itself doesn’t cause cancer, but through the release of neurotransmitters, encourages the growth of blood vessels, which are necessary for the growth of cancerous tumors. This explains why quitting the inhalation of tobacco smoke is necessary, but may not be sufficient, to preclude carcinogenesis. One also needs to avoid the nicotine which is present in many forms of cigarette replacements.
Cancer itself is never simple either. It’s almost never due to one act, or one gene, or one habit. It’s the combination of an inherited genetic pattern, a subsequent incident of damage to some DNA that didn’t get repaired as it should, on top of the predisposition to that damage or lack of repair caused by an environmental factor, such as the inhalation of tobacco leaf smoke.
How should one categorize the tobacco leaf? By defending itself chemically against ravenous insect marauders, it unwittingly launched a global industry, and became the leading cause of preventable death in the US. Wondering about why tobacco plants produce nicotine led me down neurobiochemical pathways, to agrarian philosophy, Appalachian geography, cancer research, and the science of addiction medicine. Nothing is ever one-dimensional, everything has numerous connections when we look.