Chiropractic research on the topic of inflammation and signalling has been gradually accumulating over the years, with a sharp uptick of popularity since the beginning of the pandemic. Despite the attention, there remains a lot about this topic that eludes us.
We have reported on emerging research in this area previously, with each new study publication deepening our understanding and providing fresh insight. As a refresher, here are the key takeaways of the studies we have reviewed in the past few years:
- There exists moderate quality evidence supporting an increase in neurotensin and oxytocin following HVLA adjustments. Neurotensin plays an anti-inflammatory role by downregulating the activation of pro-inflammatory cytokines. Oxytocin is important for the development and function of the immune system, and integration of neural, endocrine, metabolic, and immune information. 
- There also exists moderate quality evidence for HVLA adjustments influencing neuropeptides and inflammatory biomarkers. 
- Cervical manipulation can increase Substance P, a neurotransmitter involved in the processing of sensory stimuli, specifically pain. Although tied closely to pain pathways, Substance P can also activate the immune system, stimulate cell growth, vasodilation, and has a range of other actions. We are still learning about this neurotransmitter and there will be something to keep your eye on in future research across all fields. 
- Inflammatory markers have been found to normalise following lower back manipulations 
- Chiropractic adjustments have been found to reduce TNF (tumour necrosis factor), a pro-inflammatory mediator. 
- Spinal manipulation has been found to generate significant differences between experimental and control group inflammatory cytokines and pro-inflammatory markers. 
A study was recently published in the Journal of Manipulative and Physiological Therapeutics that provides further insight into this topic. The authors aimed to identify how neuromechanical responses changed in response to different spinal manipulative therapy (SMT) thrust magnitudes. 
Numerous other articles forming the background for the current study were cited. These including findings indicating that SMT can impact circulatory blood cytokines and oxidative stress biomarkers, and that SMT with a peak thrust force of approximately 900N increases neutrophils and monocytes activity and enhances TNF secretion. They also cited research indicating that high load cyclic compressive massage increases macrophage infiltration and elevates muscle inflammation in healthy muscle. Another noteworthy finding was that compressive massage with a lower loading magnitude stimulates the macrophage subpopulation involved in tissue repair and regeneration, rather than those involved in inflammation.
So, we know that SMT has an effect on signalling molecules in the body and may be able to indirectly modulate inflammatory pathways. We also know that different force thrusts can elicit different results, but exactly what they are has never been investigated in depth.
The current study utilised posterior-to-anterior HVLA thoracic SMT applied at the T6-T9 spine region. The adjustments were administered by a licensed chiropractor able to apply predetermined force magnitudes with consistency. Participants were divided into 3 groups; 5 participants receiving thoracic SMT with a total peak force magnitude of 800N, 9 participants receiving SMT with a total peak force magnitude of 400N, and 5 participants receiving only the pre-load force of approximately 200N. Blood samples were analysed against a panel of pro-inflammatory, anti-inflammatory, dual role cytokines, chemokines, and growth factor biomarkers. The samples were taken at baseline, before any adjustment, then immediately following the intervention, and again 20 minutes after the adjustment.
What did they find?
The present study found IFN-y and IL-5, proinflammatory cytokines were elevated in the 800N group compared to the 400N group. Interestingly, IL-6, a dual action cytokine but pro-inflammatory in chronic inflammation, was higher in the 800N group immediately after the adjustment compared to the second time point, and higher than the 400N group.
This supports the thinking that distinct force magnitudes of SMT in healthy young adults modulate a select panel of blood biomarkers related to inflammation. It appears to indicate that 800N elevated systemic pro-inflammatory cytokine levels and levels of dual role cytokine, and that 400N and control triggered an opposite effect in the short-term (although there is no clear distinction between control and 400N at this point in time).
When compared with other studies, this one is novel as previous studies used robotic apparatus instead of a clinician. While FSTT (the robotic apparatus) is capable of measuring the force and speed of SMT in a hand-on setting, it is a promising tool to advance the knowledge regarding SMT force-time characteristics and neurophysiological and biochemical responses in humans in an experimental and clinical setting. Thus, this proof of principal study adds greatly to the research going forward.
We may speculate that the similarities between these 2 groups may be driven by the preload force. The magnitude of the decrease after the 400N SMT was likely larger, at least in some cytokines compared to the control, which may be due to the thirst phase. But statistical differences are needed to support this which requires more research.
All in all, there is more work to do. But what we can see from the research is this: SMT appears to impact inflammatory cytokines at different levels at 800N and 400N. Further research will help us understand how to harness this. In the meantime, we can see a glimpse of how the adjustment may modulate the inflammatory response and this is exciting indeed.
- Haavik,H.;Niazi,I.K.; Kumari, N.; Amjad, I.; Duehr, J.; Holt, K. The Potential Mechanisms of High-Velocity, Low-Amplitude, Controlled Vertebral Thrusts on Neuroimmune Function: A Narrative Review. Medicina 2021, 57,536. https://doi.org10.3390/ medicina57060536
- Molina-Ortega F, Lomas-Vega R, Hita-Contreras F, et al. Immediate effects of spinal manipulation on nitric oxide, substance P and pain perception. Manual Therapy. 2014;19(5):411-417. doi:10.1016/j.math.2014.02.007
- Roy, R. A., Boucher, J. P, and Comtois, A. S. 2010. Inflammatory response following a short-term course of chiropractic treatment in subjects with and without chronic low back pain. Journal of Chiropractic Medicine. 9(3): 107-114. https://doi.org/10.1016/j.jcm.2010.06.002
- Teodorczyk-Injeyan. J. A., Injeyan. S., Ruegg. R., (2006), “Spinal manipulative therapy reduces inflammatory cytokines but not substance P production in normal subjects”, Journal of Manipulative and Physiological Therapeutics, 29(1): 14-21, https://doi.org/10.1016/j.jmpt.2005.10.002
- Mohammadian. P., Gonsalves. A., Tsai. C., Hummel. T., Carpenter. T., (2004), “Areas of Capsaicin-Induced Secondary Hyperalgesia and Allodynia Are Reduced by a Single Chiropractic Adjustment: A Preliminary Study”, Journal of Manipulative and Physiological Therapeutics, 23(6): 381-387, https://doi.org/10.1016/j.jmpt.2004.05.002
- Duarte FCK, Funabashi M, Starmer D, Partata WA, West DWD, Kumbhare DA, et al. Effects of Distinct Force Magnitude of Spinal Manipulative Therapy on Blood Biomarkers of Inflammation: A Proof of Principle Study in Healthy Young Adults. Journal of Manipulative and Physiological Therapeutics. 2022. 45(1):20–32.