Newsletter #316: Health Benefits of Urban Gardening 🐞
Most of the time, our immune system is our best friend.
It constantly surveils the body, and protects us from pathogens and precancerous cells. It also boasts an astonishing memory, keeping records of every enemy it has ever encountered, so that it can quickly shut down any invaders before they can cause trouble.
But sometimes, our immune system becomes our worst enemy, albeit inadvertently. It identifies a part of our own body as being a threat, and that keen memory and reactivity transform into a major liability. The result of this error is an autoimmune disease.
Research suggests that this is a growing problem. Cross-sectional data from the CDC shows that serum autoimmune antibodies have been increasing considerably since 1988, and reported incidence of most autoimmune conditions has been rising every year.
The cause of this soaring prevalence is certainly multi-factorial. Clearly, genetic predisposition plays a role in who winds up developing an autoimmune condition. But more broadly, it seems likely that a mismatch between aspects of the modern environment and our genes is leading to an escalation in autoimmunity. It has been hypothesized that interacting with microbes in the natural environment, particularly from soil, is critical for regulating the immune system. Observational studies show, for instance, that living on farms and having contact with animals is linked to reduced risk of autoimmune diseases.
More recently, researchers have started experimenting with controlled interventions to intentionally increase contact with these beneficial microbes. In a new, rather cleverly designed study, scientists in Finland conducted an urban gardening trial to see this might affect various biomarkers. Since a lot of you are probably getting your hands dirty in the garden nowadays, I thought it was worth taking a look.
This Week’s Research Highlight
Urban indoor gardening enhances immune regulation and diversifies skin microbiota.
Finnish researchers recruited 28 healthy city-dwelling participants and supplied all of them with basic indoor gardening equipment, and some common crop species (pea, radish, garlic, fava bean, lettuce, mustard, and ginger). Stuff that you could find at any nursery or large supermarket.
The only difference here was the growing medium — half of the volunteers received a microbially rich compost-based medium, and the other half (control group) received a microbially poor peat-based growing medium.
So, all of the participants were engaged in a very similar activity, and both groups were even being exposed to soil, but the dose of microbes was different, enabling the researchers to isolate the effects of microbial biodiversity on health.
Comparison of the microbial diversity and richness of the peat (placebo) versus the compost (intervention)
Everyone was instructed to grow and harvest the plants indoors, and all interactions with the growing medium were performed bare-handed. Skin swab samples and blood samples were taken before and after the horticultural intervention.
After one month, the skin microbiota of the intervention group became significantly more diverse (meaning a wider array of colonizing species. Low bacterial diversity in the skin has previously been linked to autoimmune diseases of the skin, including atopic dermatitis and psoriasis.
Furthermore, their blood work revealed a significant boost in the anti-inflammatory cytokine IL-10, which has not been shown before in prior horticultural interventions. Dermal contact with soil microbes probably would not have caused this, and this is another way that this study distinguishes itself. In the trial, all of the participants didn’t just grow the plants — they were also instructed to harvest and consume their crops. Through eating vegetables that had been grown in a microbially rich medium, the composition of the gut microbiota of the intervention group was remodeled, which in turn tilted the immune response in an anti-inflammatory direction.
The control group, meanwhile, saw no changes in either their skin microbiota or in blood-borne markers.
Finally, although this study was in adults, it’s worth noting that the most critical period for introducing these microbes is likely to be early in life. The immune system is molded in childhood, and that is often when disorders connected to immune regulation start to emerge. In a prior study from the same research group, children who played in daycare centers with forest floor vegetation experienced improvements in bacterial diversity and markers of inflammation. If you have kids, embracing gardening could be a fun and easy way to bolster your immune defenses together.
Random Trivia & Weird News
☠️ At Ainwick Castle in England lies “the world’s most dangerous garden.”
Not all gardens promote good health.
The famous Ainwick Garden in Northumberland boasts a garden that exclusively houses around 100 toxic or intoxicating plants. Some of the species featured include:
- Strychnos nux-vomica (source of strychnine)
- Hemlock
- Ricinus communis (source of ricin)
- Foxglove
- Atropa belladonna (Deadly Nightshade)
The mission of the garden, ostensibly, is drug education.
Photo credit: Phil Wilkinson
Podcasts We Loved This Week
- Richie Davidson: The science of mindfulness meditation and the four pillars of human flourishing. Via Brain Ponderings with Mark Mattson.
- Deirdre Tobias: How trustworthy is the food frequency questionnaire in evaluating dietary intake? Via Sigma Nutrition Radio.
Products We Like
Magnesium glycinate
Magnesium is a mainstay supplement for many people, myself included. Good for sleep, stress relief, cardiovascular health, etc. Furthermore, research has shown that around half of Americans do not meet the recommended daily intake for magnesium (even including supplements), so most people could probably stand to get more of this mineral. I take three tablets every evening shortly before bed.
humanOS Catalog Feature of the Week
How-to Guide to Indoor Air Quality
Environmental exposures play an underappreciated role in our health and performance. Notably, the EPA has estimated that concentrations of certain recognized air pollutants can be 2-5 times higher in indoor environments than outdoors, due to compromised dilution capacity in enclosed spaces.
There is some intriguing evidence suggesting that clearing such pollutants could make us smarter and more productive. For example, installing air filters at schools has been shown to improve exam scores in students, and study participants in “Green” buildings with excellent ventilation perform better on tests of higher-order cognitive function.
This guide will show you how to test indoor air quality, and support maintenance of better air quality in your indoor spaces, for a healthier body and mind.
Wishing you the best,
