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Study analysis · Nutrients · 2025

One herbal supplement crushed placebo for knee arthritis pain in a 39-trial analysis—but the evidence has a publication-bias problem.

In adults with knee osteoarthritis, Boswellia and some other supplements modestly improved pain and function on absolute symptom scales compared with placebo, but the review found high publication bias and mostly indirect comparisons.

Reading level
Moderate certainty
Level 1a · Systematic review of RCTs

Overview

What the study found

The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.

In simple terms

This study looked at lots of smaller experiments where people took different supplements and saw if their knee pain got better. It found that some supplements, like Boswellia, seemed to help more than others—but it didn’t prove they caused the improvement because the original studies weren’t all perfect. Think of it like guessing which ice cream flavor is best based on a bunch of surveys, some of which were a little messy.

What’s the bottom line?

Researchers combined 39 randomized trials of 4,599 people with knee osteoarthritis to compare seven supplements against placebo. They looked at pain, stiffness, and function scores.

How strong is this study?

The study did a good job collecting all the best experiments it could find, but some of those experiments didn’t follow the rules perfectly—like not telling the people measuring pain if someone got the real supplement or a fake one. That makes us a little unsure how much we can trust the results, even though the overall picture looks promising.

Reporting

40 / 100

  • COI disclosure+40/40
  • Data availabilitydata not shared
  • Code availabilitycode not shared
Methodology

56 / 100

  • Randomizationnot randomized
  • Blindingblinding unclear
  • Control group+15/15
  • Sample size (n=4599)+20/20
  • Follow-up+10/10
Publication

100 / 100

Statistical

100 / 100

  • P-values+15/15
  • Effect size+20/20
  • Confidence intervals+15/15
  • Pre-registration+15/15

Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.

Where it sits

RCT reviews

Max 100

Randomized Trials

Max 90

Reviews of Cohort Studies

Max 85

Cohort Studies

Max 72

Reviews of Case-Control Studies

Max 63

Case-Control Studies

Max 58

Cross-Sectional & Case Series

Max 50

Expert Opinion

Max 5
StrongerWeaker
Reviews of RCTs (Meta-analyses)
Level 1a
73

73 / 100

Probability of being correct

The highest quality evidence. Systematic reviews and meta-analyses that pool randomized controlled trials, giving the most reliable summary of experimental evidence.

This design can establish causation. This study is a systematic review and network meta-analysis of RCTs, which can establish causation because the included primary studies are randomized controlled trials. However, the overall confidence in causation is reduced due to methodological limitations in the included RCTs (e.g., unclear allocation concealment, blinding of outcome assessors, and high risk of bias in some domains), as well as substantial heterogeneity and publication bias.

No Conflicts

No conflicts of interest identified

No conflicts of interest or funding disclosures were reported in the study text.

Independent Analysis Safeguards

  • Study registered in CRD420251044645
  • PRISMA guidelines followed
  • Two independent reviewers for study selection, data extraction, and bias assessment
  • Cochrane Risk of Bias Tool used
  • Bayesian NMA with MCMC convergence checks (PSRF)

Although no conflicts of interest or funding sources are disclosed, the study appears methodologically rigorous with transparent protocols, independent dual-reviewer processes, and standardized statistical methods. The absence of funding disclosure is a limitation but does not, by itself, indicate bias.

Key takeaways

  1. 01

    Boswellia improved WOMAC pain by an absolute 10.58 points on a 0–96 scale, stiffness by 9.47, function by 14.00, and VAS pain by 17.26 points versus placebo.

  2. 02

    Krill oil improved function by 14.01 points.

  3. 03

    Curcumin improved VAS pain by 12.34 and function by 9.96.

  4. 04

    Collagen improved VAS pain by 16.65 and function by 9.42.

  5. 05

    Ginger improved VAS pain by 11.89.

  6. 06

    No supplement increased adverse events versus placebo; absolute risk difference was not reported.

  7. 07

    These are absolute symptom-score improvements, not relative risk reductions.

  8. 08

    For example, Boswellia’s 10.58-point WOMAC pain improvement is about an 11% absolute improvement on a 0–96 scale; on VAS, a 1–2 point change on a 0–10 scale is often considered clinically meaningful, but the reported 17.26-point VAS difference is on an unclear scale.

  9. 09

    The absolute risk of side effects did not increase, but the study did not report absolute risk differences.

  10. 10

    Rankings and benefits are uncertain because of publication bias and indirect comparisons.

Surprising findings

  • Boswellia had a SUCRA of 0.997 for stiffness—almost a 100% probability of being ranked best—despite the evidence being mostly indirect and limited by publication bias.A near-certain ranking from a network with no head-to-head trials and high publication bias is a statistical red flag, not proof of superiority.
  • The study reports a VAS pain improvement of 17.26 points, yet the methods say VAS was measured on a 0–10 scale, where a 1–2 point change is considered clinically meaningful.A 17.26-point change is impossible on a 0–10 scale, suggesting the VAS was actually 0–100 mm or that the scale reporting is inconsistent.
  • No supplement increased adverse events versus placebo, but only 5 of 41 studies specifically reported adverse events potentially associated with the intervention.Safety conclusions are only as good as the reporting, and here most studies either didn’t specify events or declared them unrelated.
  • Krill oil improved WOMAC function by 14.01 points—almost exactly the same as Boswellia’s 14.00—yet krill oil ranked poorly for VAS pain.It’s counterintuitive that a supplement can match the top-ranked one on function but not on pain, highlighting outcome-specific effects.

Practical takeaways

If you have knee osteoarthritis and want to try Boswellia, discuss it with your clinician as a possible adjunct—not a replacement for proven treatments.

Evidence certainty is moderate to low; publication bias and indirect comparisons may inflate benefits. Doses and formulations varied widely.

low-to-medium confidence

Don’t stop standard care like exercise, weight management, or prescribed medications based on this review.

The supplements were tested against placebo, not against NSAIDs or other active treatments.

medium confidence

Choose standardized supplement extracts when possible and report any side effects to a doctor.

Curcumin at high doses caused liver damage in mice; interactions with medications are possible.

low-to-medium confidence

Be skeptical of supplement rankings—SUCRA probabilities are not proof that one supplement beats another.

No head-to-head trials; rankings rely on indirect comparisons and are limited by heterogeneity.

medium confidence

Short-term use appears not to increase adverse events versus placebo, but long-term safety is unknown.

Adverse event reporting was inconsistent; only 5 of 41 studies specifically reported potentially related events.

low confidence

Why this study matters

Boswellia ranked #1—with an asterisk

In a network meta-analysis of 39 RCTs and 4,599 patients, Boswellia had the highest probability of being best for WOMAC pain (SUCRA 0.981) and stiffness (SUCRA 0.997), and also ranked first for function (0.842) and VAS pain (0.803). But the study warns that studies supporting Boswellia’s superiority rely heavily on weaker evidence.

A natural supplement outranking everything else sounds like a headline—but the ranking is probabilistic and based mostly on indirect comparisons, not head-to-head trials.

The absolute numbers: modest, not miraculous

Boswellia showed statistically significant ABSOLUTE mean improvements versus placebo: WOMAC pain 10.58 points on a 0–96 scale (95% CI 6.45–14.78), stiffness 9.47 (6.39–12.74), function 14.00 (7.74–20.21), and VAS pain 17.26 points (8.06–26.52). The WOMAC pain improvement is about 11% of the scale range.

People want to know if a supplement actually changes how they feel. A 10-point improvement on a 96-point scale is real but modest, not a cure.

Other supplements had their moments

Krill oil improved WOMAC function by an absolute 14.01 points, nearly matching Boswellia’s 14.00. Curcumin improved VAS pain by 12.34 points and function by 9.96. Collagen improved VAS pain by 16.65 and function by 9.42. Ginger improved VAS pain by 11.89.

It’s not just one miracle pill—several supplements showed some benefit, which could confuse consumers trying to choose.

Safety looked good—but reporting was messy

No supplement was associated with increased adverse events versus placebo, but the absolute risk difference was not reported. Among 41 studies reporting adverse events, only 5 specifically reported events potentially associated with the intervention; 8 said none occurred, 6 did not specify, and 22 said events were unrelated.

'No increased risk' sounds reassuring, but if reporting is inconsistent, we can’t be fully confident about long-term safety.

Publication bias is the elephant in the room

Comparison-adjusted funnel plots showed poor symmetry around the zero line for WOMAC pain, stiffness, function, and VAS pain, indicating a high likelihood of publication bias or small-study effects. That means the pooled effect sizes may overestimate true supplement benefits.

This is why supplement studies often look better in meta-analyses than they do in real life: positive results are more likely to get published.

No head-to-head trials

The evidence network was star-shaped: almost every trial compared a single supplement with placebo, with few direct comparisons between supplements. No closed loops were formed, so inconsistency testing was not performed. Rankings rely largely on indirect comparisons.

If you want to know whether Boswellia beats curcumin, this study can’t really tell you—it’s comparing each to placebo, not to each other.

Clinical context: NSAIDs have risks, supplements may be adjunct

Knee osteoarthritis is the fourth leading cause of disability. NSAIDs can cause gastrointestinal, cardiovascular, and renal problems, so patients often seek alternatives. This review suggests certain supplements may be useful adjuncts, but not replacements for proven care.

Many people turn to supplements because they can’t tolerate NSAIDs—so even modest benefits matter if safety holds up.

Want the whole report?

Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.

Standing

The people behind it

The researchers who wrote the study this analysis is built on.

Authored by

8 researchers

If this is your work, this is how we attribute it on Fit Body Science. Yuntong Zhang is listed as the lead author.