Chronic fatigue syndrome is not cancer; it’s rough, it can very debilitating but it’s usually  not deadly. Cancer often is deadly and it’s very scary but it turns out the reward many people get for surviving the big C  people  is coming down with something that very much looks like the big ‘CFS’.

Post cancer fatigue researchers cannot find one unique trigger for the fatigue they see.

Just as in ME/CFS cancer fatigue researchers have been unable to tie post-cancer fatigue to a single trigger.

The search for a cause of this fatigue has been frustrating and the parallels to ME/CFS are intriguing;  just as it’s been impossible to narrow down the list of triggers to one pathogen in ME/CFS, efforts to identify a specific trigger in cancer fatigue have been fruitless. It doesn’t matter what type of cancer they had, how much it spread,  the type of chemotherapy or radiation treatment used, how long it went on; all you need to do is get cancer and get treated for it (successfully) and you have a pretty good chance (maybe one in three) of coming down with something like ME/CFS.

Cancer patients bad luck could turn out to be our gain, however, and vice versa if  the two fields  can inform and learn from each other. The researchers are certainly eyeing each others work; cancer fatigue researchers have used HPA axis and autonomic nervous system findings  from ME/CFS studies  to inform their work so far but much else has been left unexplored.

The Study

We just saw that reduced heart rate variability levels could help explain the poor sleep in ME/CFS. Now, in this nice large study (this is cancer after all) of autonomic nervous system functioning,  norepinephrine levels and heart rate variability were examined in women cancer survivors  before and after they underwent a social stress test (Trier Social Stress Test). (The women had 10 minutes to prepare a speech and then gave it and performed  math  tasks in front of a ‘panel’).


Norepinephrine levels were increased and heart rate variability levels decreased in the more fatigued cancer survivors.


A Maladaptive Autonomic Profile

 Chronic Fight/flight activation places excessive demands on the body

Continual ‘fight/flight’ activation can place excessive demands on the body and even alter immune functioning

These findings suggested cancer fatigue is associated with what the authors called an  ‘maladptive autonomic profile’  They stated that this profile, which consists of  ‘hypoactive parasympathetic nervous systems’ and  ‘hyperactive sympathetic nervous systems’, puts ‘excessive demands’ on the body. (This is the same general profile found in chronic fatigue syndrome.)

Why ‘excessive demands’? Because the ‘fight/flight system’ prepares the body to take action. Digestion is shut down, heart rate is increased, fat and energy stores are liberated,  blood is shunted away from the organs to the muscles…..it’s a demanding energy intensive state to be in. The parasympathetic nervous system, on the other hand, promotes energy conservation.

More than just excessive energy  demands are in play. The fact that both norepinephrine and HRV activate the inflammatory response suggests the chronic HRV activation could be producing a  state of ‘sickness behavior’ in both cancer fatigue and ME/CFS patients. Sickness behavior refers to the flu-like state we encounter when we have a cold and which typifies the experiences of many people with ME/CFS and cancer fatigue.

Even if you took away the ‘fight and flight’ activation, simply having reduced ‘rest and digest’ time results in increased levels of inflammation even in healthy people; the body definitely needs it’s time to chill out and rejuvenate itself.

Vagus nerve

The vagus nerve helps to inhibit sympathetic nervous system functioning

A Key Player? The Vagus Nerve

The dysjunction between abnormal HRV readings and often normal catecholamine (eg norepinephrine) in ME/CFS has seemed puzzling given that catecholamines regulate ANS functioning but the authors noted that HRV is probably more controlled by the vagus nerve.

Since the vagus nerve regulates parasympathetic nervous system (PNS) activity,  the increased ‘fight/flight” activity in ME/CFS and post cancer fatigue  may be more a function of inadequate PNS activity than anything else. Yes,  the SNS is ‘turned on’ but it may only be  turned on because its not being regulated properly.  The problem may be more a poorly functioning vagus nerve than a revved up SNS system.  We’ll be looking more at the vagus nerve in upcoming blogs.

Cost of Decreased HRV Activity

It wasn’t so long ago that researchers didn’t know what to make of HRV findings but research has been booming. Reduced HRV findings are now associated with increased mortality in general, and cardiovascular disease.  (Cancer survivor’s, interestingly enough, have a increased  incidence of cardiovascular disease.)  One study suggested that fatigued cancer survivors have an even higher risk of heart disease.  That lead the authors of the study to state something that we, as people with ME/CFS, should all pay attention to…

Fatigue may provide an important behavioral symptom that signals the need for increased vigilance related to cardiovascular and other health risks.

Yes, they actually called for more vigilance (:)) in a disorder (cancer-related fatigue) that is associated with too much vigilance :), but never mind, ME/CFS is associated with several risk factors for cardiovascular disease including sedentariness, high levels of oxidative stress and oxidized lipids.  Being vigilant about cardiovascular risks  will include dietary measures (See the Best Diet for ME/CFS?), stress reduction, some form of ‘exercise’ and other factors we’ll be exploring later.

Accelerated Aging?

HRV tends to become reduced as we age.  Using known trends in heart rate variability the authors estimated that the cancer survivors appeared to be about 20 years older, in HRV times, than they actually were.  Surely everyone with chronic fatigue syndrome has experienced the dismay at being easily outpaced by someone who could be their grandmother.

Cancer Fatigue and Chronic Fatigue Syndrome (ME/CFS)

HRV findings are similar, a genetic risk study indicated similar cytokines (IL-1B, TNF-a, IL-6) may play a role in post-cancer fatigue and ME/CFS. Dantzer and others have proposed neuro-immune processes play a large role in producing the fatigue. Post cancer survivors have coined their own term for cognitive problems (chemo-fog).

Post cancer fatigue clinical trials have thus far mostly focused on therapies such as  exercise (positive effects), yoga (positive), mindfulness  (positive),  etc.. Post cancer fatigue patients, like fibromyalgia patients,  seem to be able to better tolerate and benefit from exercise than ME/CFS patients.

The post cancer field is growing and often contains quite large studies but is not particularly innovative or mature.  Viral studies and metabolic appear to be rare if present at all,  immune studies occur but are not particularly common, HRV studies are rare –  the field has lots of room to grow.  More insights will probably flow from chronic fatigue syndrome research to post-cancer fatigue research (if cancer researchers are open to them) at this stage.  It’ll be interesting to see what impact the CFI pathogen studies have, for instance, on fatigue research in cancer.

What we might expect from cancer fatigue study, at this point, are more fined tuned approaches to mind/body approaches. One study looking at ‘intrusive thoughts‘ (definition unclear), instance, concluded a) that intrusive thoughts were associated with worsening pain, depression and physical functioning. Another study finding that beta-blockers (autonomic nervous system regulators) reduced levels of ‘intrusive thoughts’ suggests autonomic nervous system dsyregulation could be associated with ‘intrusive thoughts’.

Final Thoughts

Similar HRV findings in ME/CFS and post-cancer fatigue patients suggests shut down of the vagus nerve (parasympathetic nervous system) may play an important role in producing the fatigue, sleep, gut and other issues in ME/CFS.


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