Readers may recall previous posts on the relationship between obesity and fibromyalgia, a chronic condition characterised by widespread pain, muscle tenderness, and decreased pain threshold to pressure and other stimuli.
Ursini and colleagues from Cantazaro, Italy, review the possible relationship between these two entities in a paper just published in Rheumatology International.
The authors review the epidemiological data showing that fibromyalgia patients have higher prevalence of obesity (40%) and overweight (30%) and discuss several mechanisms that may explain ‘the hidden link’ between these two conditions.
Proposed mechanisms include:
- impaired physical activity
- cognitive and sleep disturbances
- psychiatric comorbidity and depression
- thyroid dysfunction
- dysfunction of the GH/IGF-1 axis
- impairment of the endogenous opioid system
However, as they also note:
“…at this time is not possible to ascertain whether obesity is a cause or consequence of fibromyalgia.”
Nevertheless, the authors do suggest that the ‘causal’ relationship between the two conditions is supported by observations that fibromyalgia severity can be improved by weight loss.
This may be a good opportunity to remind readers that ‘causality’ is actually not always easy to demonstrate and it does take many levels of evidence to make any assumptions about causality convincing.
- Biological plausibility (this is usually where basic science comes in)
- Time course (this requires longitudinal studies)
- Dose-effect relationship (can be seen in cross-sectional studies)
- Strength of association (epidemiology)
- Coherence (consistency across different studies)
Add to this positive list the negative criterium that there must also be no ‘reasonable’ alternative explanations for the finding, and one may be able to eventually make a case for ‘causality’.
Unfortunately, medicine is fraught with uncertainity, as data from different studies may be conflicting or inconclusive.
This does not mean science is wrong – it just means that answers become more or less likely depending on the amount and quality of data and our understanding of the underlying biology.
This is the difference between science and pseudoscience – when new data emerges, scientists change their opinion – pseudoscientists ignore it.
Unfortunately, many prefer the ‘certainty’ of ignorance than the ‘uncertainty’ of true knowlegde.
This is why the progress of the ‘pilgrim of science’ is such an exciting and ever-fascinating journey.
I, for one, am glad that so many of my readers are willing to bear with me and join me on this expedition.
Ursini F, Naty S, & Grembiale RD (2011). Fibromyalgia and obesity: the hidden link. Rheumatology international PMID: 21476098