Accumulating evidence that CFS patients were actually more active on average than controls before becoming ill
Tom Kindlon, Irish ME/CFS Association - for Information, Support & Research
14 April 2008
The main finding in this study is that "patients with chronic, unexplained fatigue rated themselves as more active before their illness (p < 0.001)" and that "these differences remained significant for the subset of patients who met strict criteria for chronic fatigue syndrome or fibromyalgia"[1].
The authors then spend a lot of time speculating about whether this could have been an "overestimation of previous activity" and giving the "altered perception" hypothesis.
Given that they only had self-report data to go on, it is interesting to read a recent prospective population study on the illness[2]. It followed 4779 people from birth for the first 53 years of their lives. At age 53, 34 reported a diagnosis of CFS. Amongst other things, it found that "increased levels of exercise throughout childhood and early adult life and a lower body mass index were associated with an increased risk of later CFS." As it was a prospective study, there was no issue of recall bias. It also wasn't simply self-rated, as it also involved reporting by a teacher at age 13. Also they used the subject's BMI index - patients who went on to have CFS at age 53 had a (statisically significant) lower BMI than those who did not go on to develop CFS at ages 36 and 43 (before they had CFS). The authors say this "this may provide some indirect but objective evidence of increased levels of activity at these ages, especially as this difference had resolved by the age of 53 years" (when the people with CFS were no longer more active).
In the current study[1], the authors say "the only prospective cohort study of risk factors for CFS found that sedentary behavior at 10 years of age doubled the risk of self-reported CFS in adulthood"[3]. I thought I would give more information on that finding as it only related to a small percentage of the "CFS/ME" patients and doesn't show that on average patients were more inactive: in response to the question, about the amount of sport played in spare time at 10 years, 16% of the people who ever had CFS/ME by age 30 were in the "never or hardly ever" category compared to 8% in the people who didn't go on to have CFS/ME (so 8% more than expected - but it still meant that 84% in the "sometimes" and "often" categories). However the authors of the study[3] didn't combine this data in some way with a question on sports played within school: for the category "Played >2 hours/week of sport at school at 10 years", 52% of those who ever had CFS/ME by age 30 were in this category compared to 44% of those who never had CFS/ME by age 30. The unadjusted OR for this at 1.4 nearly reached
statistically significance (95% confidence intervals: 0.9 to 2.2). Some sort of combination of the two pieces of data would have been preferable - a person's body doesn't distinguish between activity done within schools hours and in their spare time.
In the current study[1], the authors point out that their "findings are congruent with those of 3 retrospective studies reporting that CFS patients perceived themselves as more active before their illness began than healthy controls"[4-6]. They also that "the high levels of physical activity reported by patients have been corroborated by their spouses, partners, or parents."[7]
With all this evidence from various sources about pre-morbid levels, researchers perhaps need to start showing more evidence before they will convince many of us of any speculative theories about CFS patients misperceiving how much activity and exercise they used to do.
[1] Smith WR, White PD, Buchwald D: A case control study of premorbid and
currently reported physical activity levels in chronic fatigue syndrome. BMC
Accumulating evidence that CFS patients were actually more active on average than controls before becoming ill
14 April 2008
The main finding in this study is that "patients with chronic, unexplained fatigue rated themselves as more active before their illness (p < 0.001)" and that "these differences remained significant for the subset of patients who met strict criteria for chronic fatigue syndrome or fibromyalgia"[1].
The authors then spend a lot of time speculating about whether this could have been an "overestimation of previous activity" and giving the "altered perception" hypothesis.
Given that they only had self-report data to go on, it is interesting to read a recent prospective population study on the illness[2]. It followed 4779 people from birth for the first 53 years of their lives. At age 53, 34 reported a diagnosis of CFS. Amongst other things, it found that "increased levels of exercise throughout childhood and early adult life and a lower body mass index were associated with an increased risk of later CFS." As it was a prospective study, there was no issue of recall bias. It also wasn't simply self-rated, as it also involved reporting by a teacher at age 13. Also they used the subject's BMI index - patients who went on to have CFS at age 53 had a (statisically significant) lower BMI than those who did not go on to develop CFS at ages 36 and 43 (before they had CFS). The authors say this "this may provide some indirect but objective evidence of increased levels of activity at these ages, especially as this difference had resolved by the age of 53 years" (when the people with CFS were no longer more active).
In the current study[1], the authors say "the only prospective cohort study of risk factors for CFS found that sedentary behavior at 10 years of age doubled the risk of self-reported CFS in adulthood"[3]. I thought I would give more information on that finding as it only related to a small percentage of the "CFS/ME" patients and doesn't show that on average patients were more inactive: in response to the question, about the amount of sport played in spare time at 10 years, 16% of the people who ever had CFS/ME by age 30 were in the "never or hardly ever" category compared to 8% in the people who didn't go on to have CFS/ME (so 8% more than expected - but it still meant that 84% in the "sometimes" and "often" categories). However the authors of the study[3] didn't combine this data in some way with a question on sports played within school: for the category "Played >2 hours/week of sport at school at 10 years", 52% of those who ever had CFS/ME by age 30 were in this category compared to 44% of those who never had CFS/ME by age 30. The unadjusted OR for this at 1.4 nearly reached
statistically significance (95% confidence intervals: 0.9 to 2.2). Some sort of combination of the two pieces of data would have been preferable - a person's body doesn't distinguish between activity done within schools hours and in their spare time.
In the current study[1], the authors point out that their "findings are congruent with those of 3 retrospective studies reporting that CFS patients perceived themselves as more active before their illness began than healthy controls"[4-6]. They also that "the high levels of physical activity reported by patients have been corroborated by their spouses, partners, or parents."[7]
With all this evidence from various sources about pre-morbid levels, researchers perhaps need to start showing more evidence before they will convince many of us of any speculative theories about CFS patients misperceiving how much activity and exercise they used to do.
[1] Smith WR, White PD, Buchwald D: A case control study of premorbid and
currently reported physical activity levels in chronic fatigue syndrome. BMC
Psychiatry 2006, 6:53. http://0-www-biomedcentral-com.brum.beds.ac.uk/1471-244X/6/53
[2] Harvey SB, Wadsworth M, Wessely S, Hotopf M: Etiology of Chronic Fatigue
Syndrome: Testing Popular Hypotheses
Using a National Birth Cohort Study. Psychosom Med. 2008 Mar 31
[3] Viner R, Hotopf M: Childhood predictors of self reported chronic fatigue
syndrome/myalgic encephalomyelitis in adults: national birth cohort study.
BMJ 2004, 329:941. http://0-www-biomedcentral-com.brum.beds.ac.uk/pubmed/15469945
[4] Riley MS, O'Brien CJ, McCluskey DR, Bell NP, Nicholls DP: Aerobic work
capacity in patients with chronic fatigue syndrome. BMJ 1990, 301:953-6.
[5] Van Houdenhove B, Onghena P, Neerinckx E, Hellin J: Does high
"action-proneness" make people more vulnerable to chronic fatigue syndrome?
A controlled psychometric study. J Psychosom Res 1995, 39:633-40.
[6] MacDonald KL, Osterholm MT, LeDell KH, White KE, Schenck CH, Chao CC,
Persing DH, Johnson RC, Barker JM, Peterson PK: A case-control study to
assess possible triggers and cofactors in chronic fatigue syndrome. Am J Med
1996, 100:548-54.
[7] Van Houdenhove B, Neerinckx E, Onghena P, Lysens R, Vertommnen H:
Premorbid "overactive" lifestyle in chronic fatigue syndrome and
fibromyalgia: an etiological relationship or proof of good citizenship? J
Psychosom Res 2001, 51:571-6.
Competing interests
No competing interest.