Dose-response efficacy of horticultural therapy for geriatric depression: a systematic review and meta-analysis of...

Horticultural therapy (HT) is a promising non-pharmacological intervention for geriatric depression. However, the optimal "dose" required for maximum clinical efficacy remains poorly defined.

To evaluate the efficacy of HT in alleviating geriatric depression and to quantify the dose-response relationship between intervention intensity and clinical outcomes.

A systematic search was conducted across eight databases (including PubMed, Embase, and Cochrane Library, etc) for randomized controlled trials (RCTs) published up to 24 February 2026. Standardized mean differences (SMD) were pooled using a random-effects model. The dose-response relationship was modeled using restricted cubic splines (RCS).

A total of eight RCTs involving 585 participants were initially identified. Systematic sensitivity analysis identified one study as a significant statistical outlier. After its exclusion, the final meta-analysis included seven studies with 435 participants. HT was associated with a significant reduction in geriatric depression scores (SMD = -0.52; 95% CI: -0.86 to -0.18; p = 0.0078). Heterogeneity remained moderate (I² = 65.6%). The RCS model revealed an exploratory, hypothesis-generating non-linear dose-response relationship (p = 0.076), suggesting that the antidepressant benefit might peak at a cumulative dose of approximately 700-800 min. However, this finding should be interpreted with caution due to the limited number of studies. Subgroup analysis indicated that the GDS-30 scale showed a marginally significant trend toward higher sensitivity to treatment effects than the GDS-15 (p = 0.055). No significant publication bias was detected via Egger's test (p = 0.936) and Begg's test (p = 0.652).

HT is an effective intervention for geriatric depression. A cumulative dose of 700-800 min represents a potential exploratory therapeutic window for maximizing efficacy while minimizing potential fatigue in frail older adults.

PROSPERO, CRD420261323722.