Unexpected Positive Nonmusculoskeletal Side Effects
Swedish Study Looks at Chiropractic

This section is compiled by Frank M. Painter, D.C.
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FROM:   J Manipulative Physiol Ther 1999 (Nov);   22 (9):   559–564 ~ FULL TEXT

Charlotte Leboeuf-Yde, DC, PhD, Iben Axén, DC, Gregers Ahlefeldt, DC,
Per Lidefelt, DC, Annika Rosenbaum, BAppSc (Chiro)d, Thomas Thurnherr, DC

Medical Research Unit,
Amtsrådhuset, Torvet, Denmark.

This retrospective study conducted in Sweden [1] has determined that about one in four chiropractic patients experiences some form of “positive nonmusculoskeletal side effect” after spinal manipulative therapy (SMT).

In addition, the percentage of patients who experience positive side effects increases with the number of spinal regions adjusted. The Swedish researchers asked all members of the Swedish Chiropractors Association (SCA) to participate in the study. Eighty-one percent of the SCA membership complied. Each doctor of chiropractic gathered data from 20 patients over a three-week period for a total of 1,504 valid patient questionnaires. Patients were included if they had been previously adjusted within the last two weeks for musculoskeletal complaints. The patients were asked if after their previous visit they ìexperienced any positive changes that do not seem to have anything to do with your back problem?

At least one positive side effect or reaction was reported by 23 percent of the respondents. The more spinal areas that were adjusted, the better their chances of experiencing at least one positive reaction:

The positive, nonmusculoskeletal reactions appear to cluster into a number of system/organ-related classifications. Of those patients who experienced them, here is the breakdown by percentage:

  • Respiratory System: 26%

  • Digestive System: 25%

  • Circulatory System/Heart: 14%

  • Eyes/Vision: 14%

The benefits experienced can also be broken down into subcategories:

  • Easier to Breathe: 21%

  • Improved Digestive Function: 20%

  • Clearer/Better/Sharper Vision: 11%

  • Better Circulation: 7%

  • Changes in Heart Rhythm/Blood Pressure: 5%

  • Less Ringing in the Ears/Improved Hearing: 4%

The authors, as is typical in research papers, are careful to point out the limitations of extrapolating the findings. They note that the study does not demonstrate whether the statistical link between treatment and reaction is causal. They assert that ìthe absence of an untreated control group makes it impossible to say whether these reactions are treatment-specific, or if they simply represent normal fluctuations of common symptoms of physiologic function. While these results are very exciting, it is clear that additional research is needed.

The Abstract

OBJECTIVE:   To investigate the frequency and types of improved nonmusculoskeletal symptoms reported after chiropractic spinal manipulative therapy.

DESIGN:   Retrospective information obtained by chiropractors through standardized interview of patients on return visit within 2 weeks of previous treatment.

SETTING:   The private practice of 87 Swedish chiropractors (response rate 81%).

SUBJECTS:   Twenty consecutive (presumably naive) patients per chiropractor (1504 valid questionnaires returned, 86% of optimal number of replies).

INTERVENTION:   Spinal manipulation with or without additional therapy provided by chiropractors.

MAIN OUTCOME MEASURES:   Self-reported improved nonmusculoskeletal symptoms (reactions).

RESULTS:   At least I reaction was reported after the previous treatment in 21% to 25% of cases. Of these responses, 26% were related to the airway passages (usually reported as "easier to breathe"), 25% were related to the digestive system (mostly reported as "improved function"), 14% were classified under eyes/vision (usually reported as "improved vision"), and 14% under heart/ circulation (about half of these reported as "improved circulation"). The number of spinal areas treated was positively associated with the number of reactions.

CONCLUSION:   A minority of chiropractic patients report having positive nonmusculoskeletal reactions after spinal manipulative therapy but such reports cluster predominantly around specific symptoms. It would be interesting to find out if these can be verified objectively and, if so, to investigate if they are caused by the treatment or if they are signs of natural variations in human physiology.

From the Full-Text Article:


Chiropractors are occupied primarily with the treatment of painful backs; however, historically they have dealt with many kinds of ailments. More than 100 years ago, D.D. Palmer, the founder of chiropractic, reported his first chiropractic patient to have been a partially deaf man, in whom he diagnosed “a vertebra racked from its normal position.”1 The man’s hearing was restored soon after a chiropractic adjustment to the fourth thoracic vertebra. [1]

Since then, many chiropractors have had the dual role of treating painful conditions of the spine and attending to various symptoms and signs indicative of visceral conditions. This practice is based on the concept that abnormalities in the spinal column may cause nerve interference, which in turn can induce disorders or diseases involving segmentally related visceral organs. Spectacular “cures” have been reported, based solely on clinical observations.

In modern chiropractic practice, particularly in Scandinavia, clinicians appear to be moving away from the organic concept to the muskuloskeletal symptomatic relief model. Thus, in a recent Swedish study, a nonmuskuloskeletal problem was reported as the primary symptom only by 1 of 625 chiropractic patients. [2]

The 2 main reasons for this shift may be an improved academic standard, resulting in a reduced number of practitioners who are willing to base their practice solely on anatomicphysiologic-based hypotheses and a desire on the part of chiropractic practitioners to be included in mainstream health care, making it necessary to curtail the scope of practice to make it more evidence-based.

Much has been written on the subject of spinal manipulative therapy (SMT) and somatovisceral conditions. Nansel and Szlazak, [3] in a review of 350 articles appearing over the last 75 years on this subject, conclude that suitable evidence is lacking for the rationale of the somatovisceral theory. The authors argue instead that somatic dysfunction of the spine may create signs and symptoms that mimic internal organ disease. Hence, the removal of the spinal dysfunction may remove the symptoms and signs of an organic disease or disorder that never was there in the first place.

Nonetheless, although there seems to be a general belief that chiropractic treatment of organic diseases is “politically incorrect,” many chiropractors obviously remain open to this possibility. [4] Hence, although they likely believe that their main task is the treatment of painful conditions of the spine, they also accept the possibility that SMT may have, as an extra bonus, an unexpected positive effect on other bodily functions. A recent survey of a small sample of Danish chiropractors showed that almost all thought that SMT may at times have an effect on various organic disorders. [5]

This belief is understandable, if patients and chiropractors think that there may be a causal correlation between the treatment and various improvements, regardless of their type. After all, in the clinical world most temporal evidence (such as any improvement after treatment) is taken for granted. The daily clinical situation does not provide a control group. Our goal was to find out how frequently patients report nonmuskuloskeletal symptomatic improvements and to find out more about the types of such reactions that patients believe to be associated with chiropractic treatment. Because we could find no statistics on this issue in the literature, we decided to collect our own data.

This was carried out as a project in which a local Swedish team learned how to conduct a study of this type under supervision by the first author. The steps of project planning, data collection, and data analysis were preceded by a series of lectures and workshops. All local activities were coordinated and supervised by one individual. Data were analyzed by the entire project group.


This study showed that approximately 25% of patients, when asked, report improvements of various symptoms that appear to be nonmuskuloskeletal in origin. It is interesting that many of these positive side effects are sufficiently similar to allow several relatively large subgroup classifications. Improved breathing, digestion, circulation, and vision were the most common examples.

Eight cases of improved hearing were also identified. Curiously, all these patients had been treated in the thoracic spine (exact level unknown), although always in combination with some other spinal region. Hence, it is not known if they were associated with the fourth thoracic vertebra, as in the case of D.D. Palmer's famous patient. [1]

Having identified the frequency and types of reactions, two questions now arise. Was the reporting of reactions correct, and was the link between treatment and reactions causally associated?

      Was the reporting of reactions correct?

Many of these presumed reactions were familiar to the research team. Hence, the face validity in relation to the types of reactions appeared reasonable. Overreporting as a result of bias among the patients and the chiropractors was unlikely, considering that the patients were naïve (none had sought care primarily for a nonmuskuloskeletal condition). The belief of the research team was that there is no tradition among Swedish chiropractors in general to emphasize this aspect of patient care. This opinion is supported by the previous clinical epidemiologic study of Swedish chiropractors, in which only 1 of 625 patients consulted primarily for a nonmuskuloskeletal symptom. [2]

Underreporting could of course also have occurred, for example, if the chiropractor's demeanor indicated that these types of reactions do not occur or should not be reported or if the patients did not understand what was meant by the question or could not recall previous reactions. However, the research team, in personal contact with all the chiropractic participants, formed the opinion that Swedish chiropractors, in general, are genuinely interested in getting more objective information on this topic. Patients were uniformly informed, including being shown a schematic drawing based on experiences during extensive pilot testing of the survey instrument. The recall period was limited to a maximum of 2 weeks.

Another problem is that our estimate of reported reactions (23%) refers to the general patient population. Thus it is not known if the proportion of reactions would be the same in specific subpopulations, such as in patients who have specific organic problems. In other words, the appropriate denominators for the various reactions are unknown.

The clinical reality of these reports is also unclear. For example, some of the “scattered” reactions seem to lack credibility, such as “better prostatic function” (sexuality/sex organs), “not so sensitive to sun” (skin), “back of thigh drier” (skin), and “stronger hair” (other). Some patients may be more sensitive or imaginative than others, such as the person who reported 6 rather peculiar reactions.

However, most patients who noticed an improvement report only 1 reaction, and there are some consistently recurring statements, such as “easier to breathe” and “improved hearing,” which support chiropractic folklore. Nonetheless, it would be necessary to confirm their veracity through objective tests. This is an important issue, as shown in a previous uncontrolled study of SMT in asthmatic patients. Although these patients often reported improved lung status after the treatment, this response did not correlate well with the objective tests that measured the true extent of bronchospasm. [6]

      Was the link between treatment and reaction causally associated?

Whether the statistical link between treatment and reaction is causal or not cannot be shown with the present study design. Although a temporal link is a prerequisite for a causal association, the absence of an untreated control group makes it impossible to say whether these reactions are treatment-specific or if they simply represent normal fluctuations of common symptoms of physiologic function.

In the case of SMT and asthma, again, we are aware of 2 high-quality, published, randomized controlled trials that both failed to show that chiropractic SMT is an effective method to treat asthma. [7, 8] These results surely contrast with the subjective reporting of improvement in the study without a control group. [6] Obviously, unless more controlled randomized trials are conducted in this area, this issue will never be resolved.

Another factor we looked at was the dose-response gradient. Our hypothesis was that if these reactions were indeed the result of a physiologic rather than a psychologic process, the number of reactions per patient would be positively associated with the number of areas treated. This was confirmed. The occurrence of reported reactions increased gradually with the number of areas treated to be about twice as many in those having been treated in 4 areas than those treated in only 1 area.


Some patients did report an improvement of nonmuskuloskeletal symptoms after chiropractic SMT. Whether these reports reflect real physiologic improvements or are based on subjective impressions is not known; if they are real, it is unclear whether they are the result of the treatment or whether they are coincidental events. However, the finding of a positive dose response does warrant further investigation. We do not wish to purport any specific hypotheses about this issue. We simply wish to point out that this subject is suitable for further research. We hope that our estimates of the frequency with which the various reactions occur can help in the planning of additional studies into this domain. Ideally, such studies would measure validated physiologic responses of symptomatic and asymptomatic subjects in controlled randomized trials.


  1. Palmer DD.
    Textbook of the science, art and philosophy of chiropractic.
    Portland Printing House, Portland (Ore)1910: 406-407

  2. Leboeuf-Yde C Hennius B Rudberg E Leufvenmark P Thunman M.
    Chiropractic in Sweden: a short description of patients and treatment.
    J Manipulative Physiol Ther. 1997; 20: 507-510

  3. Nansel D, Szlazak M.
    Somatic Dysfunction and the Phenomenon of Visceral Disease Simulation:
    A Probable Explanation for the Apparent Effectiveness of Somatic Therapy
    in Patients Presumed to be Suffering from True Visceral Disease

    J Manipulative Physiol Ther 1995 (Jul); 18 (6): 379–397

  4. Chance MA Peters RE.
    While the jury is out…Chirop.
    J Aust. 1997; 27: 97

  5. Franz C Skov S.
    Kiropraktik og O-lidelser.
    Kiropraktoren. 1997; 10: 8-9

  6. Jamison JR Leskovec K Lepore S Hannan P.
    Asthma in a chiropractic clinic: a pilot study.
    J Aust Chiropractors' Assoc. 1986; 16: 137-143

  7. Nielsen NH Bronfort G Bendix T Madsen F Weeke B.
    Chronic asthma and chiropractic spinal manipulation: a randomized clinical trial.
    Clin Exp Allergy. 1994; 25: 80-88

  8. Balon J, Aker PD, Crowther ER, Danielson C, Cox PG, O'Shaugnessy D, et al.
    A Comparison of Active and Simulated Chiropractic Manipulation
    as Adjunctive Treatment for Childhood Asthma

    N Engl J Med 1998 (Oct 8); 339 (15): 1013–1020



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