Plants can save us.
Plants release organic compounds which have been proven to boost our ability to fight off viral infections. Here’s how we can reap that benefit in the era of COVID-19 and the global call to #stayhome.
All plants release phytoncides as part of their daily metabolic process. Phytoncides are VOCs (volatile organic compounds) which possess antimicrobial, antibacterial and antifungal qualities that defend plants against insects, animals, diseases and decomposition, by creating a protective microclimate around them. Think of it as an invisible cloud of biologically active agents that help plants survive a long list of potential attacks.
Over the past 20 years, breakthrough research has uncovered some of the ways phytoncides positively interact with our immune system on a cellular level. A few studies have focused specifically on how our NK (natural killer) cells are boosted by phytoncides, as they’re our very first immune defense against alien pathogens.
Why our NK (natural killer) cells matter.
Viral infections deplete our white blood cells, either by damaging (called cytotoxicity) or killing them (called apoptosis). When our white blood cell numbers are low due to cell damage or death, our immune systems become weakened and less capable of fighting off disease.
NK cells are a type of white blood cell, and our immune systems’ first defense against viral infections. They’re distinct from other defense cells, as they don’t rely on any “cell memory” (i.e., immunity) to react. As our ‘first responders’ they indiscriminately and immediately attack foreign pathogens, triggering the call for back-up from other white blood cells. Our ‘second responder’ cells target specific pathogens, once our immune systems collect more information on the specific type of attack and needed response.
The link between NK cells and plant phytoncides.
To explore the links between plants and our immune systems, researchers primarily focused on outdoor plants. Test subjects spent several days immersed in different types of forests, with their NK cell levels measured before, during and after. Increased NK cell levels from three days spent in a forest lasted for more than 30 days. Older reports indicate different forests release different amounts of phytoncides. One hectare (nearly 2.5 acres) of pine forest releases 5 kg (approximately 11 pounds) of phytoncides in a day, whereas the same sized juniper forest releases 30 kg (approximately 66 pounds) in the same timeframe.
Researchers concluded that time spent immersed in nature — an activity coined “forest bathing” — stimulated NK cell production, resulting in a stronger immune system. In this moment of viral pandemic, if you have a forest nearby that you can safely access without public transport, it’s a great time to take a (solitary) walk and take a few deep breaths. Research indicates your immune system can get a boost, on top of all the psychological and emotional benefits that being in nature brings.
But what if you must #Stayhome?
Spending a lot of time indoors isn’t unusual in modern society. Well before COVID-19, and as far back as 2001, surveys found nearly 90 percent of Americans and Europeans spend around 22 hours inside every day. We may be splitting up that time indoors between our homes, offices, restaurants, supermarkets and cars, but the reality remains: we are highly accustomed to spending very little time outside our man-made environments.
If you live in an area where being outdoors is largely banned, you may be feeling some anxiety or unease about spending so much time inside, particularly if you’re also consuming a stream of headlines about accelerating infection rates and chaotic official responses, while trying to keep your productivity up in home office, entertaining and educating your kids, and virtually checking in on friends and family around the world. The stress of this situation has the potential to negatively impact your immune system. But, this is the time when you need those NK cell levels to be fully primed.
What we know about NK cells and COVID-19.
What we know so far is that COVID-19 is a disease caused by a virus (SARS-CoV-2), which seems to primarily attack our lung cells. And as we see with the current statistics, 80%+ of confirmed individuals who’ve contracted SARS-CoV-2, experience very mild symptoms of the disease. This is good news: many people have recovered from COVID-19 because their immune systems have been able to fight it off without serious symptoms or even medical intervention.
Right now, researchers are rapidly working on vaccine and antiviral therapies to treat COVID-19 with immunotherapy, specifically focused on stimulating NK cell activity. This isn’t the first time that NK cells have been studied or used in combating viral diseases or coronaviruses. A 2004 research study measured the level of NK cells in patients who had contracted SARS, another coronavirus, and found the levels of NK cells in survivors to be significantly lower after their bodies combated the disease.
With the high likelihood of catching SARS-CoV-2, how many NK cells we have before infection matters. Maintaining a healthy immune system now is something we can influence by simply breathing in the phytoncides that plants release to stimulate NK cell production.
Boost your phytoncide intake at home with indoor plants.
In this time of COVID-19, staying indoors and minimizing our time outside is what is both strongly advised and socially responsible. We can still get the phytoncide boost to our immune systems from indoor plants, by caring for the ones we already have and by potentially bringing more greenery into our homes.
Different indoor plant species release differing levels of phytoncides, and research suggests their size also matters. The ability of plants to release enough phytoncides to stimulate our NK cell activity, has mainly been studied in plants taller than 30cm (nearly 12 inches), with broad leaves and/or pointed tips. These characteristics indicate that the most common houseplants (tropicals and succulents) are also potentially the most effective in supporting our immune systems.
I uncovered research started in 1973 that measured phytoncide release levels across 300 species of indoor plants. Here’s a shortlist of plants from that report with high phytoncide release levels (common plant names in parentheses):
- Alocasia macrorrhiza (Giant Taro)
- Aspidistra elatior (Cast Iron Plant)
- Anthurium andreanum (Flamingo Flower)
- Begonia masoniana (Iron Cross Begonia)
- Kalanchoe blossfeldiana (Christmas Kalanchoe)
- Nephrolepis exaltata (Boston Fern)
- Monstera deliciosa (Monstera)
- Hedera helix (English Ivy)
- Ficus benjamina (Weeping Fig)
- Ficus elastica (Rubber Plant)
- Rosmarinus officinalis (Rosemary)
- Dracaena draco (Dragon Tree)
- Sansevieria grandis (Snake Plant)
- Syngonium podophyllum (Arrow Head Plant)
- Dieffenbachia maculata (Dumbcane)
- Yucca elephantipes (Yucca)
- Agave americana (American Aloe)
- Clivia miniata (Bush Lily)
- Schefflera actinophylla (Umbrella Tree)
- Crassula arborescens (Money Tree)
- Philodendron scandens (Heartleaf Philodendron)
- Asparagus sprengeri (Asparagus Fern)
As the world reacts to this pandemic in chaotic real-time, one thing is clear: staying indoors right now can help get us through this. Maintaining a strong immune system is also important. Let’s focus on what’s within our control: our mindset, our actions and how we manage our energy, immune systems and time. #Stayhome. And spend some time with your houseplants. They can save us.
Who am I?
I’m admittedly a plant person. I founded horticure.com 16 months ago, a platform I’d conceived initially to address my own irritatingly bad ability to keep houseplants alive. I killed, with precise consistency, nearly every plant I brought inside, across various homes in Chicago, New York City and now Berlin.
I designed Horticure to be simple: if you need the help of a horticulturist or plant expert to maintain your indoor plants, you can book one to come directly to your home or office, or get needed plant care advice via video chat.
TL;DR: Keep your plants alive, so they can continue doing the work of supporting your immune health.
Spend time taking deep breaths around your houseplants. If you need help maintaining them, ask questions and get free advice via our Facebook group, “Ask a Horticulturist”. We’re here to help.
Sources and Further Reading:
- 1979: Phytoncide: https://encyclopedia2.thefreedictionary.com/Phytoncide
- 2004, The Involvement of Natural Killer Cells in the Pathogenesis of Severe Acute Respiratory Syndrome: https://watermark.silverchair.com/ajcpath121-0507.pdf
- January 2008: Visiting a Forest, but Not a City, Increases Human Natural Killer Activity and Expression of Anti-Cancer Proteins: https://journals.sagepub.com/doi/abs/10.1177/039463200802100113
- August 2009: Effect of Phytoncide from Trees on Human Natural Killer Cell Function: https://journals.sagepub.com/doi/pdf/10.1177/039463200902200410
- 2015: Assortment of plants for improving indoor air quality in medical institutions: https://ibn.idsi.md/ro/vizualizare_articol/77213
- February 2016: Roles of natural killer cells in antiviral immunity: https://www.sciencedirect.com/science/article/abs/pii/S1879625715001583?via%3Dihub
- 2016: Changes in Air Ions Concentration depending on Indoor Plants Activity: https://agronomy.emu.ee/running_issue/running_issue_11.pdf
- 2018: The Indoor Generation: Facts & Figures: https://www.velux.com/article/2018/indoor-generation-facts-and-figures
- May 2018: ‘Forest Bathing’ Is Great for Your Health. Here’s How to Do It: https://time.com/5259602/japanese-forest-bathing/
- March 2019; Viral Infection of Human Natural Killer Cells: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6466310/
- June 2019: Natural Killer Cells in the Lungs: https://www.frontiersin.org/articles/10.3389/fimmu.2019.01416/full
- March 2020: Cryo-EM structure of the 2019-nCoV spike in the prefusion conformation: https://science.sciencemag.org/content/367/6483/1260
- March 2020: Breadth of concomitant immune responses prior to patient recovery: a case report of non-severe COVID-19: https://www.nature.com/articles/s41591-020-0819-2
