This website claims that getting regular adjustments by a Chiropractor helps your immune system and thus can help prevent getting or lessen the severity of disease. It supports this claim with links to some studies. Is this claim accurate or are there any flaws in the analysis on that website?
As discussed in the comments this particular claim will be tricky to either prove or falsify. It is easy for researchers to measure white blood cell counts or levels of immune activity, but more difficult to translate this into overall immune function, which is itself a vaguely defined term. Lets look at the research cited by the claimant.
The nervous system, the endocrine system, and the immune system are inextricably linked, like a three-legged stool. (For some great articles on this concept, click here, here, here, and here)
The first 5 linked papers support the plausibilty of the claim by looking at links between systems in the body, that could connect chiropractic therapy to the immune system. This in itself is not really evidence.
One recent pioneering study,"Enhancement of in vitro interleukin-2 production in normal subjects following a single spinal manipulative treatment"(click here for the article) clearly demonstrated an increase in IL-2 levels and also in the function of T-cells, which are key players in the immune system's army of cells, following chiropractic adjustment. The authors concluded that chiropractic adjustment can influence the biological immune response.
This is the first actual evidence for the claim. However, the study only shows that chiropractic treatment increases the production of a messenger molecule (IL-2) that is involved with a lot of things in the body, including immune response. The cited research has not yet discussed how IL-2 affects immune response, but that it does.
In another elegant study by Selano et al, "The Effects of Specific Upper Cervical Adjustments On The CD4 Counts of HIV Positive Patients'" (Chiropractic Research Journal 1994; 3(1): 32-39), the effects of six months of regular chiropractic care on the immune system function of HIV patients was measured. At the end of six months of care, the patients who had received regular adjustments had a 48% increase in the number of CD4+ T cells (p=0.06), whereas the patients who were not adjusted had an 8% decrease in CD4+ cells.
In this study, the treatment group was a group of people with atypical immune systems, so the results might not be completely applicable to HIV negative people. CD4+ T cells are a type of immune cell that is attacked by the HIV virus. HIV causes AIDS by destroying the CD4+ T cells, and therefore severely weakening the immune system. In a healthy person, I do not know if more CD4+ cells are necessarily better and the claimant does not show any evidence that more are better.
Tangentially related research Cohrane is an organization who's entire purpose is to evaluate the evidence for medical claims like this one. They are my go to source for evidence based medicine. One of their reviews looked at evidence about "Massage therapy for people with HIV/AIDS" and found some evidence for positive outcomes due to massage therapy. However they say that, "it may be that massage therapy can improve[s HIV patients'] body's ability to fight the disease; however, this is not yet convincingly proven."
A series of studies published in the Journal of Manipulative and Physiological Theraputics (JMPT) by Brennan and Triano showed that several types of immune system cells, including phagocytes, neutrophils, and PMNs, showed increased biological activity after chiropractic adjustment.
This seems like an accurate summary of the articles, but it doesn't necessarily mean that there is a substantial longterm effect that will help ward of disease.
The next linked study discusses 100 year old statistics about chiropractic care during the 1918 Spanish flu epidemic. These seem more like fun historical facts than real data, and the link is broken, so I can't even review them properly.
The last two links don't seem to only tangentially relevant to the main claim. The text in the claim doesn't seem to match the content of the second paper.
Throughout the paper the claimant uses hedging language to back away slightly from the headline claim. He says "chiropractic adjustment can influence the biological immune response" but says influence rather than improve. At another point, "these studies all suggest" but they don't actually show that the claim is true.
My independent research A google scholar search led me to a scientific review of research into chiropractic treatments, Basic Science Research Related to Chiropractic Spinal Adjusting: The State of the Art and Recommendations Revisited, which has a section entitled, Immune Function Studies.
Chiropractic field practitioners assert that SM produces improvement in several visceral conditions, including some that are thought to involve perturbed immune function. Although chiropractic theory suggests that immunologic effects might be expected through neurologically mediated mechanisms, few studies have addressed this topic. Most of the evidence has been drawn from basic science studies that gave broad mechanistic support but did not specifically examine SM and its effect on immune function.
In plain English, most research looks at the mechanisms that chiropractic adjustment may influence the immune system, rather than actual outcomes. The research can show that CD4+ cells are boosted, but not show that this translates into fewer sick days or reduced severity of infectious diseases.
Conclusion The claim is plausible but far from proven. The immune system has a lot of working parts which act in concert to fight infectious disease. Chiropractic adjustment has been shown to affect some of these parts, but there is no evidence it protects against infectious disease.