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Social connectedness as a mediator for horticultural therapy's biological effect on community-dwelling older adults: Secondary analyses of a randomized controlled trial

Contact Information


Ted Kheng Siang Ng,

Biopsychosocial; Gardening; Horticulture; IL-6; Inflammatory biomarker; Nature; Older adults; Social connectedness; Well-being.


Background: Elevated levels of inflammatory marker and a lack of social connectedness are two prominent risk factors for developing dementia and depression. Horticultural therapy (HT) has been shown to improve social connectedness and inflammatory markers. However, the underpinning mechanisms of HT remained unknown. Within this study, we hypothesized that improved social connectedness mediates the effects of HT on IL-6 levels. Methods: The present study is a secondary analysis of a randomized controlled trial investigating the bio-psycho-social effects of HT. Social connectedness was operationalized as positive relationships with others (PRWO), a sub-scale of the Ryff's scale of psychological well-being. IL-6 was quantified using a commercial ELISA kit. Outcomes were assessed at baseline, 3-month and 6-month post-intervention. Mediation analyses with bootstrapping were run to investigate our primary hypothesis. All analyses were controlled for covariates. Results: We recruited 59 participants (78% women; 67.10 ± 4.31 years). 29 participants partook in HT and 30 participants were included in the waitlist control group. At baseline, social connectedness was significantly correlated with IL-6 levels (β = -0.12, 95% CI = -0.21 to -0.03, p = 0.008). Furthermore, social connectedness at 3-month significantly mediated the effects of HT on IL-6 levels at 6-month (β = 0.32, 95% CI = 0.09 to 0.54, p = 0.005; β = -0.25, 95% CI = -0.45 to -0.05, p = 0.016). Conclusions: These findings highlight the critical roles of social connectedness as a social determinant of health in eliciting HT's biological effects. When administering HT, interventionalists should consider social connectedness as a modifiable factor for ameliorating increased inflammation in older adults.


Ng, T. K. S., Gan, D. R. Y., Mahendran, R., Kua, E. H., & Ho, R. C. (2021). Social connectedness as a mediator for horticultural therapy's biological effect on community-dwelling older adults: Secondary analyses of a randomized controlled trial. Social science & medicine (1982), 284, 114191.





Conent Area

Ted Kheng Siang Ng

EWB-Related Construct

(1) goal pursuit; (2) life satisfaction; (3) positive affect; (5) sense of meaning

Study Design

Species or Study Population

(5) RCT

Sex (%Female)


Age (Mean, SD)

intervention: 67.21, 4.52
control: 67.00, 4.18

Younger Controls?


Longitudinal Data?


Sample Size



Horticultural therapy

Ethnicity (%white)


Inclusion Criteria

Aged between 60 to 85 years
English and/or Chinese speaking
Were able to provide informed consent
Function independently
MoCA score minimum 22

Exclusion Criteria

Have dementia
Have history of major psychiatric conditions e.g. schizophrenia, bipolar disorder
Have history of chronic medical conditions e.g. cancer, stroke, Parkinson disease
Are undergoing another intervention at the same time
Have significant visual or hearing impairment
Have marked upper and lower limb motor difficulties ​

EWB Measures

(1) Ryff's scales of psychological well-being

Non-EWB Behavioral


Physiological Measures

(3) vascular: Blood: Interleukin-6

Brain IMaging Modality

Brain IMaging Paradigm


Brain Region/Circuit


Biological Measures


Other Neural Measures

Data Availability?


Data Avalability Details


Diagnostic Measures

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