Physical activity at age 11 years and chronic disabling fatigue at ages 13 and 16 years in a UK birth cohort, 2018, Crawley et al

[Andy]

Abstract
Objective To investigate associations of physical activity at age 11 years with chronic disabling fatigue (CDF) at ages 13 and 16 years.

Design Longitudinal birth cohort.

Setting South-West England.

Participants Adolescents enrolled in the Avon Longitudinal Study of Parents and Children.

Outcomes and exposures We identified adolescents who had disabling fatigue of >6 months' duration without a known cause at ages 13 and 16 years. Total and moderate-to-vigorous physical activity and sedentary time at age 11 years were measured by accelerometry over a 7-day period.

Results A total physical activity level 100 counts/min higher at age 11 years was associated with 25% lower odds of CDF at age 13 years (OR=0.75 (95% CI 0.59 to 0.95)), a 1% increase in the proportion of monitored time spent in moderate-to-vigorous activity was associated with 16% lower odds of CDF (OR=0.84 (95% CI 0.69 to 1.01)) and a 1-hour increase in sedentary time was associated with 35% higher odds of CDF (OR=1.35 (95% CI 1.02 to 1.79)). Disabling fatigue of only 3–5 months’ duration at age 13 years had weaker associations with physical activity, and CDF at age 16 years was not associated with physical activity at age 11 years.

Conclusions Children who had chronic disabling fatigue at age 13 years had lower levels of total and moderate-to-vigorous physical activity and more sedentary time 2 years previously, but this association could be explained by reverse causation.

Open access at http://adc.bmj.com/content/early/2018/01/30/archdischild-2017-314138 if you can stomach it.

Crawley continues her "chronic disabling fatigue" = ME fiction
"Here we use data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to investigate whether levels and patterns of physical activity at age 11 years20 are associated with ‘chronic disabling fatigue’ (CDF, a proxy for clinically diagnosed CFS/ME) at ages 13 and 16 years."

 

[James]

Total and moderate-to-vigorous physical activity and sedentary time at age 11 years were measured by accelerometry over a 7-day period.

Surely not the same accelerometry that children found stigmatizing, so subjective reporting was the only possible recourse that researchers respecting children and adolescents wishes had at their disposal

 

[Londinium]

As I've remarked before, a journal allowing the sentence 'CDF, a proxy for CFS/ME' through peer review is presumably one that would also publish a study on the effects of cough syrup on lung cancer in which the primary outcome is 'cough, a proxy for carcinoma'.

The bit that jumps out is was the conclusion's mention of reverse causation. On the face of it, that's obvious in any longitudunal study but also raises the question: did they exclude 11 year olds who already met, or were close to meeting, the criteria for CDF? Otherwise all one's shown is that kids who are ill at 13 may also have been ill at 11...

 

[Sean]

'cough, a proxy for carcinoma'.

Respiration, a predictor of long-term mortality.

 

[Arnie Pye]

Total and moderate-to-vigorous physical activity and sedentary time at age 11 years were measured by accelerometry over a 7-day period.

Surely not the same accelerometry that children found stigmatizing, so subjective reporting was the only possible recourse that researchers respecting children and adolescents wishes had at their disposal

I've googled, but I can't find a definition of accelerometry that works in this context. What is it?

According to dictionary.com an accelerometer is "an instrument for measuring the acceleration of a moving or vibrating body".

 

[Skycloud]

or vibrating body".

What have they been doing to those poor children?

 

[Andy]

I've googled, but I can't find a definition of accelerometry that works in this context. What is it?

According to dictionary.com an accelerometer is "an instrument for measuring the acceleration of a moving or vibrating body".

Activity tracker, such as a Fitbit or similar.

 

[Valentijn]

I've googled, but I can't find a definition of accelerometry that works in this context. What is it?

It's an actometer. The accelerometer in an actometer is used to help measure movement - steps, changes in position, etc.

 

[Arnie Pye]

Thanks, @Andy and @Valentijn

 

[James]

Actometers that were specified for use in 2007 PACE trial protocol for patients at baseline but considered an unnecessary encumbrance on recovered participants at the end of the trial.
Dutch FITNET did use ankle bracelet actometers but did not include data from them in the final published report.
A reasonable person may think actometers should have some warning attached when used in research, perhaps along the lines of this device could seriously damage your hypothesis.

 

[Amw66]

Open access at http://adc.bmj.com/content/early/2018/01/30/archdischild-2017-314138 if you can stomach it.

Crawley continues her "chronic disabling fatigue" = ME fiction
"Here we use data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to investigate whether levels and patterns of physical activity at age 11 years20 are associated with ‘chronic disabling fatigue’ (CDF, a proxy for clinically diagnosed CFS/ME) at ages 13 and 16 years."

The subtle definition change from previous paper now has a life of it' s own. Perhaps we should invent labels for other conditions to trivialise them too? Chronic disabling headache- brain tumour.....

 

[Snow Leopard]

Guys, epidemiological research like this often isn't perfect but is better to be done than not done, in terms of hypothesis generation, even with the dodgy criteria. The key is not to assume the conclusions are generalisable.

 

[NelliePledge]

Guys, epidemiological research like this often isn't perfect but is better to be done than not done, in terms of hypothesis generation, even with the dodgy criteria. The key is not to assume the conclusions are generalisable.

But Crawley and cronies will no doubt be generalising just see any of her talks

 

[Amw66]

The subtle definition change from previous paper now has a life of it' s own. Perhaps we should invent labels for other conditions to trivialise them too? Chronic disabling headache- brain tumour.....

Out of interest, are there any other illnesses that are arbitrarily renamed ?

 

[Dolphin]

So as the authors say the definition at 16 years is more rigourous as it also requires the patients to report significant fatigue along with the parents' report.

Outcomes—CDF at ages 13 and 16 years

Our methods for defining CDF at age 13 (median 13.1, IQR 13.1–13.2) and 16 (median 16.6, IQR 16.5–16.8) years have been described previously.6 7

In brief, mothers were asked whether their child had been feeling tired or lacking in energy over the last month (yes, no); how long the tiredness had lasted (<3 months, 3–5 months, 6 months to 5 years, >5 years); how many days their child had missed school because of tiredness; and whether the tiredness/lack of energy had prevented the child from taking part in hobbies, sport or leisure activities (not at all, only a little, quite a lot, a great deal).

The questionnaires asked whether the teenager snored (never, sometimes, often), whether the mother thought the fatigue was due to the teenager playing too much sport and whether the teenager took regular medication (free text question: ‘Please indicate below any medicines your child has used in the last 12 months’).

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).

At age 16 years, children could only be classified as having CDF if they scored ≥19 (out of 33) on the Chalder Fatigue Scale.22 23

According to our definitions, the prevalence of CDF of >6 months’ duration at ages 13 and 16 years was 1.1% (76/6720) and 1.5% (84/5756), respectively.

To reduce overlap between primary exposures and outcomes, we excluded children with >5 years’ duration of fatigue at ages 13 (10 out of 76 children) and 16 (11 out of 84 children) years.

After these exclusions, 66/6720 children at age 13 years and 73/5756 children at age 16 years were classified as having CDF (of 6 months’ to 5 years’ duration).

We also performed a sensitivity analysis in which we redefined our outcome at age 13 years to include only children whose disabling fatigue had been of 3–5 months’ duration (78/6720 (1.2%)).

 

[Dolphin]

Not important, but I don't understand the underlined bit.

Total physical activity was calculated as the average accelerometer counts per minute (cpm) over the full period of valid recording.

To facilitate interpretation, associations with total physical activity were calculated per 100 cpm.

This measure was chosen because it approximates the difference in physical activity between boys and girls and therefore provides a useful reference point.20

All minutes of recording with a total of ≥3500 accelerometer counts were classified as moderate-to-vigorous physical activity.

The threshold of 3500 cpm was derived from a calibration study in a subsample of 246 ALSPAC children.25

We analysed moderate-to-vigorous physical activity as a mean daily proportion of total monitored time.

This allowed us to investigate whether the volume of physical activity or (occasional) intensity of physical activity was more important in predicting risk of CDF.

Sedentary time was the mean daily amount of time (hours per day) when the accelerometer recorded ≤100 cpm.

 

[Dolphin]

They only excluded people whose fatigue had lasted 5 years or more. There was a 2nd category they included:

6 months to 5 years

So people's fatigue at age 13 could have started before the age of 11 in which case it would not be surprising they might have been doing low activity levels.

When they just restricted the analyses to those whose disabling fatigue had lasted 3-5 months, this is what they found:

Disabling fatigue of 3–5 months' duration at age 13 years was less strongly associated with total physical activity (raw data unadjusted OR=0.88 (95% CI 0.76 to 1.03); imputed data fully adjusted OR=0.86 (95% CI 0.75 to 0.99)), moderate- to-vigorous physical activity (raw data unadjusted OR=0.94 (95% CI 0.82 to 1.07); imputed data fully adjusted OR=0.90 (95% CI 0.80 to 1.01)) and sedentary time (raw data unadjusted OR=1.22 (95% CI 0.99, to 1.51); imputed data fully adjusted OR=1.20 (95% CI 1.00 to 1.44)).

Significant results are found only when the 95% confidence intervals are both on the same side of one. When one is below 1 and the other is above 1, the result is not statistically significant.

 

[Dolphin]

Physical activity at age 11 years and CDF at age 16 years

[..]

Median levels of total and moderate-to-vigorous physical activity were lower at age 11 years in children who had CDF at age 16 years, but with weak evidence for these differences (table 1). Total physical activity (OR=0.94 (95% CI 0.77 to 1.15)), moderate-to-vigorous physical activity (OR=0.96 (95% CI 0.82 to 1.13)) and sedentary time (OR=1.16 (95% CI 0.89 to 1.51)) were not associated with CDF at age 16 years (table 3).

 

[Dolphin]

The main limitation of our study is that children were not assessed by a doctor, which is why we describe our outcome as ‘chronic disabling fatigue’, a proxy for CFS/ME.

At age 13 years, our classification was based only on parental report of fatigue, with limited data on degree of disability.6

We may have excluded teenagers whose parents under-reported the impact of fatigue and/or included teenagers whose parents overestimated fatigue or its impact.

However, our CDF outcome at age 16 years combined parental data with a child-completed Chalder Fatigue Questionnaire (CFQ) score.7

At this age, we classified children as not having CDF if they had a CFQ score <19, a threshold which has high sensitivity and specificity for CFS/ME in adults.23

The threshold used to define minutes of moderate-to-vigorous physical activity from the accelerometer data affects estimates of physical activity.

To facilitate comparisons with the other ALSPAC papers, we have used the threshold of 3500 cpm.25

We recognise that others have suggested that the Evenson et al37 cut-point of ≥2296 cpm may have wider validity and reliability in the target group, particularly for population-based samples.38

 

[Dolphin]

We cannot be sure to what extent the association of physical activity at age 11 years with CDF at age 13 years reflects reverse causation.

In a UK paediatric CFS/ME clinical cohort, the median (IQR) self-reported duration of illness for children aged under 12 years was 12 (7–23) months and in children aged 12–18 years it was 18 (11–28) months.3

Furthermore, our previous analysis of CDF among children in the ALSPAC cohort at age 13, 16 and 18 years showed that 75% of children recovered after 2–3 years.10

These two studies suggest that the proportion of children in this study whose chronic fatigue would be longer than 2 years’ duration would be low, and that any association of physical activity at age 11 years with CDF at age 13 years would not reflect reverse causation.

However, analysis of electronic primary care data in the UK showed that children with CFS/ME had substantially higher healthcare needs than matched population controls for at least 10 years before their diagnosis.39

This suggests that parents have underestimated the duration of their child’s fatigue, or that paediatric CFS/ME begins in a mild form which develops into more severe CFS/ME.

This is plausible if the milder form of CFS/ME does not lead to notable absences from school or college.