Obesity in adolescents with chronic fatigue syndrome: an observational study, 2016, Norris et al

Andy

Andy

Retired committee member
This has come up as a reference in a new study, so I thought I'd create a separate thread for it.
Abstract
Objective Identify the prevalence of obesity in patients with chronic fatigue syndrome (CFS) compared with healthy adolescents, and those identified with CFS in a population cohort.

Design Cross-sectional analysis of multiple imputed data.

Setting Data from UK paediatric CFS/myalgic encephalomyelitis (CFS/ME) services compared with data collected at two time points in the Avon Longitudinal Study of Parents and Children (ALSPAC).

Patients 1685 adolescents who attended a CFS/ME specialist service between 2004 and 2014 and 13 978 adolescents aged approximately 13 years and 16 years participating in the ALSPAC study.

Main outcome measures Body mass index (BMI) (kg/m2), sex-specific and age-specific BMI Z-scores (relative to the International Obesity Task Force cut-offs) and prevalence of obesity (%).

Results Adolescents who had attended specialist CFS/ME services had a higher prevalence of obesity (age 13 years: 9.28%; age 16 years: 16.43%) compared with both adolescents classified as CFS/ME in ALSPAC (age 13 years: 3.72%; age 16 years: 5.46%) and those non-CFS in ALSPAC (age 13 years: 4.18%; age 16 years: 4.46%). The increased odds of obesity in those who attended specialist services (relative to non-CFS in ALSPAC) was apparent at both 13 years (OR: 2.31 (1.54 to 3.48)) and 16 years, with a greater likelihood observed at 16 years (OR: 4.07 (2.04 to 8.11)).

Conclusions We observed an increased prevalence of obesity in adolescents who were affected severely enough to be referred to a specialist CFS/ME service. Further longitudinal research is required in order to identify the temporal relationship between the two conditions.
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Open access at https://adc.bmj.com/content/102/1/35
 
They used CDC and NICE (ie. “adolescents reported by their mothers to have experienced fatigue lasting >6 months that was associated with absence from full-time school or that had prevented them from taking part in activities ‘quite a lot’ or ‘a great deal’.“) and speculated that the obesity was related to lack of activity.

But it would seem more likely in a neuro-immune illness (if selection criteria were strict) that metabolic changes and/or disorders were a result of injury to the hypothalamus, rather than “laziness”.
 
specialist services - (age 13 years: 9.28%; age 16 years: 16.43%)
CFS/ME in ALSPAC - (age 13 years: 3.72%; age 16 years: 5.46%)
non-CFS in ALSPAC - (age 13 years: 4.18%; age 16 years: 4.46%)

So in the general population there is no significant difference between ME/CFS and non-ME/CFS, only those who attended the specialist services showed higher prevalence of obesity. One could equally well conclude that whatever the specialist services are doing is causing the obesity or that obese patients were being disproportionately referred to specialist services regardless of severity.
 
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From https://www.nhs.uk/conditions/obesity/, my bolding
"Day-to-day problems related to obesity include:

  • breathlessness
  • increased sweating
  • snoring
  • difficulty doing physical activity
  • often feeling very tired
  • joint and back pain
  • low confidence and self-esteem
  • feeling isolated"
which potentially means that obese patients may be being referred to specialist CFS services inappropriately. Or even that some of the changes caused by obesity have the same or similar effect to ME. Whatever the reason, I bet some CBT will sort them out....
 
Andy said:
From https://www.nhs.uk/conditions/obesity/, my bolding
"Day-to-day problems related to obesity include:

  • breathlessness
  • increased sweating
  • snoring
  • difficulty doing physical activity
  • often feeling very tired
  • joint and back pain
  • low confidence and self-esteem
  • feeling isolated"
which potentially means that obese patients may be being referred to specialist CFS services inappropriately. Or even that some of the changes caused by obesity have the same or similar effect to ME. Whatever the reason, I bet some CBT will sort them out....
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Anecdotally, organisations like the CFIDS Association say that metabolic syndrome is more common in some patients too.

It includes central obesity and insulin resistance.
 
This 2016 study was discussed quite extensively on PR.

As background - there were two data sources, the ALSPAC survey and specialist clinics. For both, data was obtained at ages 13 and 16.

Diagnosis of CFS in the ALSPAC survey was not done by a clinician. Young people whose mothers felt that the fatigue was caused by playing too much sport were excluded, which probably helped to skew the CFS sample towards young people with higher BMIs.

ALSPAC Age 13 years diagnosis method:
Our method for defining chronic disabling fatigue at 13 years has been described previously.14 In brief, we identified adolescents reported by their mothers to have experienced fatigue lasting >6 months that was associated with absence from full-time school or that had prevented them from taking part in activities ‘quite a lot’ or ‘a great deal’. We excluded those whose mothers thought that the fatigue was caused by playing too much sport, who snored often and who had other illnesses that could cause fatigue (based on self-reported medication use).
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From what was written in the paper, it seemed as though only 15% of the data points from the specialist clinic had BMI information. Here's a post I made on PR:

There's something a bit weird with the imputation of missing data. If you look at the supplementary material on imputation, it appears that,
for specialist services data at both 13 and 16, only around 15% of the 1680 data points had BMI information;
for ALSPAC data at both 13 and 16, only around 40% of the data points had CFS data and only about 40% had BMI information.

The supplementary material says missing data was imputed using auxiliary variables due to, among other things, 'their strong hypothesised association with CFS/ME'. Auxiliary variables used included
Family Adversity Index
Life Difficulties
School Absences in Year 11
Academic attainment
Anxiety and depression measures

Different variables were used for the imputation in each data source (Alspac and Specialist).

(There was a mention of 99 data points created by imputation for each of data sources, but I'm not sure how that works as they would have had to create a lot more data points than 99 to make up for the missing data.)

But anyway, the supplementary material gives the results from the 'complete case analysis' which presumably is the analysis of the data points that had no missing data. Here's the complete case results (with the results that were reported in the main body of the paper in brackets for comparison).

...............................Alspac No CFS ........... Alspac CFS...............Specialist CFS
13 years
Mean BMI..................20....................................20..............................21...............
% obese....................3.57 (4.18).......................3.92 (3.72).................9.23 (9.28)

16 years
Mean BMI.......... .......21.....................................21..............................22.............
% obese...................3.94 (4.46).........................6.00 (5.46).................6.8 (16.43)

So, the differences between the three groups look a lot less impressive in the un-imputed data. Instead of an upward trend from 9% to 16% obese over three years in the specialist group, there is a downward trend from 9% to 7%.

That makes a big difference - there isn't evidence in the complete data points that the CFS children are growing more massive as each year passes.

The imputation process is not well explained. The raw data however is reported as being available - so that is something.

My conclusion: there may possibly be a very small difference between the BMI's and obesity prevalence of non-CFS and CFS adolescents but there's enough murkiness about what was actually done with the data that I would not be getting excited until someone without an agenda analysed the data afresh.
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Hutan said:
My conclusion: there may possibly be a very small difference between the BMI's and obesity prevalence of non-CFS and CFS adolescents but there's enough murkiness about what was actually done with the data that I would not be getting excited until someone without an agenda analysed the data afresh.
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The bump due to imputation is suspicious, but there were no differences in the ALSPAC data and the overall proportion was small, so any claims that obesity somehow is a precipitating or perpetuating factor for CFS in children is obviously false.
 
Correction: Obesity in adolescents with chronic fatigue syndrome: an observational study
The Editor of the journal has agreed to the request from the authors that the ethics statement should be changed to improve its clarity. The new statement is as follows: ‘The CFS/ME patient data used in this study were collected as part of routine clinical practice and anonymised for the National Outcomes Database. Under the Governance Arrangements for Research Ethics Committees (September 2011), ethical review is not required for research limited to the use of previously collected, non-identifiable patient information.’
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https://adc.bmj.com/content/105/2/e1
 
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