The aim of this systematic review was to update the current level of evidence for spinal manipulation in influencing various biochemical markers in healthy and/or symptomatic population.
Various databases were searched (inception till May 2023) and fifteen trials (737 participants) that met the inclusion criteria were included in the review. Two authors independently screened, extracted and assessed the risk of bias in included studies. Outcome measure data were synthesized using standard mean differences and meta-analysis for the primary outcome (biochemical markers). The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used for assessing the quality of the body of evidence for each outcome of interest.
There was low-quality evidence that spinal manipulation influenced various biochemical markers (not pooled). There was low-quality evidence of significant difference that spinal manipulation is better (SMD -0.42, 95% CI – 0.74 to -0.1) than control in eliciting changes in cortisol levels immediately after intervention. Low-quality evidence further indicated (not pooled) that spinal manipulation can influence inflammatory markers such as interleukins levels post-intervention. There was also very low-quality evidence that spinal manipulation does not influence substance-P, neurotensin, oxytocin, orexin-A, testosterone and epinephrine/nor-epinephrine.
The authors concluded that spinal manipulation may influence inflammatory and cortisol post-intervention. However, the wider prediction intervals in most outcome measures point to the need for future research to clarify and establish the clinical relevance of these changes.
The majority of the studies were of low or very low quality. This means that the collective evidence is less than reliable. In turn, this means, I think, that the conclusions are misleading. A more honest conclusion would be this:
There is no reliable evidence that spinal manipulation influences inflammatory and cortisol levels.
As for the clinical relevance, I would like to point out that it would not be surprising if chiropractors could one day convincingly show that spinal manipulation do influence various biochemical markers. Many things do! If you fall down a staircase, for instance, plenty of biochemical markers will be affected. This, however, does not mean that throwing our patients down the stairs is of therapeutic value.