Tis the Season for Forest Immunity
It’s that time of year when many of us trot out to the woods or the tree lot to collect a woody symbol of the festive holiday season. Seeking a Christmas tree in the forest, purchasing a holiday bush from a tree lot, putting up a fake tree, or avoiding foliage altogether impacts your microbiome in different ways.
Chopping down your own tree leads you to the forest which in and of itself is healing. The Japanese have long studied the physiological benefits of forest environments and coined the term Shinrin-yoku, a concept defined as “taking in the atmosphere of the forest”. Research has shown an association between forest exposure and lower cortisol levels, blood pressure, and heart rate.1 Pinenes, the major chemical constituents of pine resin, have strong antiseptic, antimicrobial, antifungal, and expectorant properties.2 Pine aromatics, known as phytoncides, stimulate the activity of the Natural Killer (NK) cells of your innate immune system, which fight viral infections and cancer.3 Finally, breathing in the damp, fresh, piney smell of the forest produces immediate relaxing therapeutic effects as anatomically, the olfactory system is closely connected to the limbic system of the brain. Signals are sent to the amygdala, hypothalamus, and cingulate gyrus which are the regions of your brain that regulate emotions, your autonomic nervous system, and attention, respectively.4
Effects of Aromatics and Exercise on the Microbiome
The aromatics do even more than stimulate the immune system; they likely also benefit the microbes that live on the skin and perhaps even the gut. Recent research has shown that essential oils can promote growth of healthy microbes in the gut. Specifically, a study done on pigs showed that oregano and thyme essential oils increase Lactobacillus and Bifidobacterium.5 These are the same bacteria that are found in many probiotics – but you can increase them just by smelling essential oils!
”In other words, just breathing in the forest is good for you.”
But you’re in the forest to chop down a tree! This requires breaking a sweat. Moderate exercise also supports your microbiome, increasing the diversity of microbes in your gut and leading to production of microbial metabolites that coax the immune system into an anti-inflammatory state.6
Picking up that tree to haul it out of the forest has additional benefits. Getting your hands dirty supplies your body with additional microbes. (And you thought sap was annoying.) In fact, sap provides a nutrient rich reservoir that can feed microbes.7 Sap in maple trees is actually pushed to the surface and leached from the tree with microbes doing the heavy lifting.8
Do all of these benefits end when you get home with your festive greenery? It does not. The increased NK activity lasts for 7 days, and the increased number of NKs last for at least a month!3
Just one trip per month to the forest can have your immune system in tip top shape.
Farmed or Free-Range
Many of the benefits of chopping down a tree are lost when you purchase a tree from a tree lot. Besides missing out on some “forest therapy”, the trees in lots are grown on tree farms where they are sprayed with pesticides. There are 8 common herbicides, fungicides, and pesticides currently used in holiday tree farming practices in the US.
The fungicide chlorothalonil acts by both killing microbes on the tree and in the soil below. Exposure to this fungicide can also reduce microbes in people through inhibiting several oxidizing enzymes including dehydrogenase, catalase, and acid phosphatase.9
The herbicides atrazine, hexazinone, and simazine act by entering the weeds through the root system and interfering with photosynthesis10, 11 and because of the deleterious ecological effects, some European countries have banned their use.12
Glyphosate, better known as Round-Up, is one of the more common pesticides used to kill weeds that might compete with crops. Glyphosate works by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase. However, as this enzyme is key to the metabolic activity of microbes, the use of glyphosate results in microbial death, including helpful human microbes. Long-term exposure to glyphosate is being linked to many diseases including Celiac disease, Parkinson’s disease, and several types of cancer.13
Carbaryl, chlorpyrifos, and dimethoate are insecticides that kill both pests and beneficial insects (like bees).14, 15 All three work through similar mechanisms of action by blocking an enzyme (acetylcholinesterase) that is shared between insects and humans, exposure to these insecticides can produce short-term acute toxicity in people. Furthermore, studies have suggested a potential association with exposure to these insecticides and neurological toxicity, developmental disorders, and autoimmune diseases.16, 17, 18
With all of these chemicals used to grow Christmas trees, you may want to kick your Christmas tree to the curb earlier than usual. However, pesticides are usually applied in summer months, nearly 5 months before their harvest, meaning much of the residue is washed off with rain or degraded by sunlight. Therefore surface exposure does not pose much of a risk, but it’s worth keeping tree water away from your pets and curious children and to wash sap from commercial trees off your hands quickly. One solution to help limit exposure to pesticides is to order an organic tree online.
Real or Artificial, which is better?
Artificial trees, popular with people who have allergies to pine or don’t want to clean up pine needles, do not not contain pesticides. However, before you go rocking around your Christmas tree, you should know that fake trees are often made of plastic like polyvinyl chloride (PVC). PVC contains toxic additives like phthalates which are hormone disruptors.19 While some people like PVC trees for the safety aspect of flame resistance, toxic heavy metals such as lead, tin, and cadmium are used in the manufacturing.20 It is far preferable to safeguard against the risk of a house fire by keeping your tree from drying out with daily watering.
With all of the chemicals surrounding Christmas trees, real and artificial, you may not want to touch one with a thirty-nine and a half foot pole. But you can put your inner Grinch to bed as there are so many things that can help us nurture a healthy microbiome, and repair some of the damage done by our various exposures.
- Eat those chestnuts after they’ve roasted on an open fire.
- Dash through some snow and get some exercise.
- Smell those cinnamon, peppermint, and pine essential oils.
- And bring joy to the world and your microbiome!
- Park BJ, Tsunetsugu Y, Kasetani T, Kagawa T, Miyazaki Y. The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): evidence from field experiments in 24 forests across Japan. Environ Health Prev Med. 2010;15(1):18-26. doi:10.1007/s12199-009-0086-9
- Salehi B, Upadhyay S, Erdogan Orhan I, et al. Therapeutic Potential of α- and β-Pinene: A Miracle Gift of Nature. Biomolecules. 2019;9(11):738. Published 2019 Nov 14. doi:10.3390/biom9110738
- Li Q. Effect of forest bathing trips on human immune function. Environ Health Prev Med. 2010;15(1):9-17. doi:10.1007/s12199-008-0068-3
- Farrar AJ, Farrar FC. Clinical Aromatherapy. Nurs Clin North Am. 2020;55(4):489-504. doi:10.1016/j.cnur.2020.06.015
- Ruzauskas M, Bartkiene E, Stankevicius A, et al. The Influence of Essential Oils on Gut Microbial Profiles in Pigs. Animals. 2020;10(10):1734. doi:10.3390/ani10101734
- Clauss M, Gérard P, Mosca A, Leclerc M. Interplay Between Exercise and Gut Microbiome in the Context of Human Health and Performance. Front Nutr. 2021;8:305.
- Jennifer J. P, Maria C. F. A Comprehensive Review of Maple Sap Microbiota and Its Effect on Maple Syrup Quality. Food Rev Int. 2020;0(0):1-20. doi:10.1080/87559129.2020.1788579
- Information About Sap In Trees. Accessed December 17, 2021. https://www.gardeningknowhow.com/ornamental/trees/tgen/what-is-tree-sap.html
- Baćmaga M, Wyszkowska J, Kucharski J. The influence of chlorothalonil on the activity of soil microorganisms and enzymes. Ecotoxicol Lond Engl. 2018;27(9):1188-1202. doi:10.1007/s10646-018-1968-7
- Ma L, Selim HM. Atrazine retention and transport in soils. Rev Environ Contam Toxicol. 1996;145:129-173. doi:10.1007/978-1-4612-2354-2_2
- Hunter WJ, Shaner DL. Removing hexazinone from groundwater with microbial bioreactors. Curr Microbiol. 2012;64(5):405-411. doi:10.1007/s00284-012-0086-7
- Gunasekara AS, Troiano J, Goh KS, Tjeerdema RS. Chemistry and fate of simazine. Rev Environ Contam Toxicol. 2007;189:1-23. doi:10.1007/978-0-387-35368-5_1
- Leino L, Tall T, Helander M, et al. Classification of the glyphosate target enzyme (5-enolpyruvylshikimate-3-phosphate synthase) for assessing sensitivity of organisms to the herbicide. J Hazard Mater. 2021;408:124556. doi:10.1016/j.jhazmat.2020.124556
- Winterlin W, Walker G, Luce A. Carbaryl residues in bees, honey, and bee bread following exposure to carbaryl via the food supply. Arch Environ Contam Toxicol. 1973;1(4):362-374. doi:10.1007/BF01985436
- Dimethoate - an overview | ScienceDirect Topics. Accessed December 17, 2021. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/dimethoate
- US EPA O. Chlorpyrifos. Published December 29, 2014. Accessed December 17, 2021. https://www.epa.gov/ingredients-used-pesticide-products/chlorpyrifos
- Gels JA, Held DW, Potter DA. Hazards of insecticides to the bumble bees Bombus impatiens (Hymenoptera: Apidae) foraging on flowering white clover in turf. J Econ Entomol. 2002;95(4):722-728. doi:10.1603/0022-0493-95.4.722
- Romo V. EPA Will Ban A Farming Pesticide Linked To Health Problems In Children. NPR. https://www.npr.org/2021/08/18/1029144997/epa-will-ban-a-farming-pesticide-linked-to-health-problems-in-children. Published August 18, 2021. Accessed December 17, 2021.
- Hlisníková H, Petrovičová I, Kolena B, Šidlovská M, Sirotkin A. Effects and Mechanisms of Phthalates’ Action on Reproductive Processes and Reproductive Health: A Literature Review. Int J Environ Res Public Health. 2020;17(18):E6811. doi:10.3390/ijerph17186811
- Department of Human Services | PVC – a major source of phthalates. Accessed December 17, 2021. https://www.state.nj.us/humanservices/opmrdd/health/pvc.html