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Natural Medicine Journal

July 2, 2019

Gardening Promotes Production of Brain-Derived Neurotrophic Factor in the Elderly

Significant increase seen after just 20 minutes

Kurt Beil

ND, LAc, MPH
The mental health benefits of gardening have been recognized for centuries and confirmed by modern-day science, but a recent study is among the first to explore the mechanism of action using biomarker data.

Reference

Park S-A, Lee A-Y, Park H-G, Lee W-L. Benefits of gardening activities for cognitive function according to measurement of brain nerve growth factor levels. Int J Environ Res Public Health. 2019;16(5):760.

Study Objective

To determine the effects of gardening on measures of healthy neurological function.

Design

Pre-post intervention study

Participants

Forty-one senior citizens (mean age 76.6 ± 6.0 years) living in Seoul, South Korea

Intervention

Participants engaged in 20 minutes of low-to-moderate gardening activities, including cleaning the plot, digging, fertilizing, raking, planting, and watering.

Outcome Measures

Blood samples were taken before and after gardening, to provide the following biomarker data:

  • Brain-derived neurotrophic factor (BDNF), promoting growth of neurons and formation of new synaptic connections, often linked to healthy memory and cognitive function
  • Vascular endothelial growth factor (VEGF), promoting growth of new blood vessels, often linked to improved cognitive function
  • Platelet-derived growth factor (PDGF), promoting growth of multiple cell types, including glial cells and blood vessels, often linked to various health states

Key Findings

After 20 minutes of gardening, there was an 8.4% increase in BNDF and a 13.5% increase in PDGF (P≤0.05 and P≤0.001, respectively). Changes in VEGF were not statistically significant. No significant outcome differences between male and female participants were measured.

Practice Implications

It has been said that a garden is both a place and a process for healing.1 The activities and environment of the garden provide opportunities for physical exercise, but also mental reflection, social and ecological connection, and establishment of self-confidence and sense of accomplishment. Witnessing the transformation of vegetable and mineral matter over time, even after just 20 minutes of labor, is a therapeutic event as old as our species. We respond to gardens because they are a part of our history, our mythology, and our culture. Simply the presence of gardens on-site at a nursing home increased residents’ overall perceived health, suggesting that the natural aesthetic features of the garden activated inherent biophilic mechanisms that impact subjective experience.2,3

This is the first known study to directly investigate biomarkers of neurological function as a mechanism of action for improvement in mental health.

Gardening has been recommended for mental health for centuries. Dr Benjamin Rush, one of the signers of the United States Declaration of Independence, noted that “digging in the garden” brought significant benefits to patients during his tenure overseeing America’s first psychiatric facility.4 The professions of horticultural therapy (HT) and therapeutic horticulture (TH) have been advocating for the healing benefits of gardening for many decades,5 something any gardener knows inherently.

A recent meta-analysis of the benefits of gardening supported these positive effects in multiple areas, including mental (depression, positive affect, self-esteem), physical (weight loss), and psycho-social (sense of community, sense of purpose, life satisfaction).6 It is no surprise that this current study would show increase in biomarkers related to the creation of healthy brain structure and function.

Mental health/stress

This is the first known study to directly investigate biomarkers of neurological function as a mechanism of action for improvement in mental health. Other studies have demonstrated the positive impact that gardening has on clinical aspects of mental health, such as reduction of depression and psychological impacts of stress.7,8 And some studies have shown that gardening is a useful activity for stress recovery, helping to return both mood and salivary cortisol to baseline levels after exposure to a stressor.9 Recent studies have even shown that gardening has positive effects on mental illness, with horticulture therapy programs being successfully used at inpatient psychiatric facilities in the United States and United Kingdom.10,11

More directly related to the current study, there is evidence that gardening is beneficial for reducing dementia-associated memory deficits, as well as behavioral issues, in elderly patients.4 Regarding the specific findings of this study, it is no great surprise that gardening would increase BDNF. Physical activity has long been known to facilitate BDNF production and associated memory and cognitive function.12

Physical activity

This study adds to the vast amount of research demonstrating the importance of regular physical activity for all aspects of health, including mental health.13 It is known that physical activity increases blood and lymphatic flow, regulates inflammatory and anti-inflammatory cytokines, and stimulates production of neurotransmitters and the beneficial neurotrophic growth factors like BDNF and PDGF, measured here.

The activities in this study were selected because they were regular, simple activities often recommended for elderly people as part of a daily health maintenance routine. These activities are classified as low-to-moderate physical activity (LMPA) according to their designation as between 2.8 and 4.5 on the metabolic equivalents (METs) scale.14 Other studies have investigated the effect of LMPA gardening activities on physiological measures like heart rate, oxygen saturation, and caloric expenditure, all with positive results.15

Gardening facilities and programs

The evidence supporting HT/TH is growing (pun intended), and with it the willingness to utilize these methods for therapeutic benefit. A 2015 survey found over 110 therapeutic horticulture gardens on, near, or associated with US hospitals or other healthcare facilities.16 Military organizations around the world are even beginning to use therapeutic horticulture programs for combat veterans with posttraumatic stress disorder (PTSD), such as the Gardening Leave program in Scotland and the Veterans Greenhouse and Gardens Program (Boston).17,18

Limitations

The lack of a control group significantly limits the empirical usefulness of this study. Future studies may want to utilize a sedentary waitlist control group to experimentally demonstrate cause-effect relationships between gardening and neurotrophic growth factors. Similarly, comparison of gardening with other activities of similar METs could help determine any benefits unique to gardening vs other types of LMPA.

Measurement of neurotrophic growth factors in this study does not demonstrate the clinical health benefits of gardening. Future studies wanting to demonstrate the impact of gardening on cognitive function could include psychometric scales for assessing memory and mood (eg, Wechsler Memory Scale, Beck Depression Inventory).

This was a small pilot study with a limited number of participants. A large, better-powered study would have greater statistical validity and might be able to detect significance in other outcome measures (eg, VEGF).

Conclusion

Gardening is an ancient activity with multiple holistic benefits. This simple activity can be practiced by almost any patient and is likely to be helpful for almost any medical condition without risk of adverse side effects. Research is just beginning to validate the many ways that “digging in the garden” is beneficial for our total health and wellbeing, including how the physical activity of gardening can have such impressive and lasting mental effects.

As the saying goes, “Gardening is cheaper than going to therapy, plus you get tomatoes.” Researchers, clinicians, policy makers, and healthcare administrators may want to investigate horticultural therapy and therapeutic horticulture programs to reduce disease burdens and improve physical and mental health in their populations of interest.

Categorized Under

Kurt Beil

ND, LAc, MPH

Kurt Beil, ND, LAc, MPH, is a naturopathic physician and licensed acupuncturist and holds a master’s degree in public health focused on the benefits of green space as a sustainable public-health promotion tool. He did his postdoctoral work at the Helfgott Research Institute on biomarker and psychometric assessment of the restorative and therapeutic effects of natural vs built urban environments. Dr Beil has been an advisor to the Children & Nature Network’s “Nature Research Database” and was the founding cochair of the Nature & Health subcommittee of the Intertwine Alliance in Portland. He also moderates a Facebook group NDs for Nature for the naturopathic medicine community on the clinical health benefits of contact with nature. Dr Beil maintains a clinical naturopathic and Chinese medicine practice in Happy Valley, Oregon, focusing on chronic disease. He can be reached via email or www.drkurtbeil.com.

References

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  3. Grinde B, Patil GG. Biophilia: does visual contact with nature impact on health and well-being? Int J Environ Res Public Health. 2009;6:2332-2343.
  4. Detweiler MB, Sharma T, Detweiler JG, et al. What is the evidence to support the use of therapeutic gardens for the elderly? Psychiatry Investig. 2012;9(2):100-110.
  5. American Horticultural Therapy Association. AHTA Definitions and Positions. https://www.ahta.org/ahta-definitions-and-positions. Published 2019. Accessed June 9, 2019.
  6. Soga M, Gaston KJ, Yamaura Y. Gardening is beneficial for health: a meta-analysis. Prev Med Reports. 2017;5:92-99.
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  8. Gonzalez MT, Hartig T, Patil GG, Martinsen EW, Kirkevold M. Therapeutic horticulture in clinical depression: a prospective study of active components. J Adv Nurs. 2010:66(9):2002-2013.
  9. van den Berg AE, Custers MHG. Gardening promotes neuroendocrine and affective restoration from stress. J Health Psychol. 2010:1-10.
  10. Pieters HC, Ayala L, Schneider A, Wicks N, Levine-Dickman A, Clinton S. Gardening on a psychiatric inpatient unit: cultivating recovery. Arch Psychiatr Nurs. 2019;33(1):57-64.
  11. de Seixas M, Williamson D, Barker G, Vickerstaff R. Horticultural therapy in a psychiatric in-patient setting. BJPsych Int. 2017;14(4):87-89.
  12. Roig M, Nordbrandt S, Geertsen SS, Nielsen JB. The effects of cardiovascular exercise on human memory: a review with meta-analysis. Neurosci Biobehav Rev. 2013;37(8):1645-1666.
  13. Mandolesi L, Polverino A, Montuori S, et al. Effects of physical exercise on cognitive functioning and wellbeing: biological and psychological benefits. Front Psychol. 2018;9(APR):1-11.
  14. Park SA, Lee KS, Son K-C. Determining exercise intensities of gardening tasks as a physical activity using metabolic equivalents in older adults. HortScience. 2011;46(12):1706-1710.
  15. Park S, Shoemaker C, Haub M. A preliminary investigation of exercise intensities on gardening tasks in older adults. Percept Mot Skills. 2008;107(07):974-980.
  16. George DR, Rovniak LS, Kraschnewski JL, Hanson R, Sciamanna CN. A growing opportunity: community gardens affiliated with US hospitals and academic health centers. Prev Med Reports. 2015;2:35-39.
  17. Atkinson J. An Evaluation of the Gardening Leave Project for Ex-Military Personnel with PTSD and Other Combat-Related Mental Health Problems. Glasgow: The Pears Foundation; 2009.
  18. US Department of Veterans Affairs. VA Boston Healthcare Center. Veterans Greenhouse and Gardens Program: the healing properties of dirt. https://www.boston.va.gov/features/Veterans_Greenhouse_and_Gardens_Program_The_Healing_Properties_of_Dirt.asp. Updated May 11, 2015. Accessed June 11, 2019.

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