24 Studies looking at Afib and Physical Activity - a layperson's guide.

A layperson’s look at 24 studies into exercise and Afib

I’m no scientist, but I have drawn together what I could find.  However, be sure to read the caveats at the end re the quality of some of the data plus an explanation of some terminology and abbreviations.  I tried hard not to be biased, but I'm only human so some may have crept in.  I also stopped at 24 studies because it was taking over my life!!

1.       1. Kunutsor et al 2021– Meta analysis of 23 cohort studies

Excludes case controls; also excludes athletes or competitive or endurance sportspeople; quality of evidence low to medium; selection bias; lacks temporality ((i.e., lacks a link))

Most Physically active vs Least                   -1% risk of AF

Men only                                                             +20%

Women only                                                      -9%

 

Conclusion was that lower mortality in active people far outweighs risk of Afib even in high intensity individuals

 

 

2.       Wen-Gen Zhu et al 2016 “Sex differences in association of AF and physical activity

Total PA exposure           -2% risk of AF     (statistically insignificant)

Intense PA                          +7%                       (statistically insignificant)

 

Total PA               Men Only                            +18%                     Women only      -8%

Age 50 plus         Men Only                            +58%

Intense PA          Men only                             +12%                     Women only      -8%

 

This report concludes that long term sports increases AFib risk in competitive athletes, but intermediate or high cardio fitness reduces AFib.  No definition of high PA given.

 

 

3.       Zhengbiao Xue et al 2020 “Dose responsive relationship of cv fitness with incidental Afib”

This study states that intermediate or high cardiovascular fitness decreases AF

 

4.       Bosomworth 2015 “Atrial Fibrillation and PA – should we exercise caution? “

Sedentary                           Men      high risk of AF                    Women                high risk of AF

Moderate PA                                     lower risk of AF                                                 lower risk of AF

Intense PA*                                       increases AF#                                                    reduces risk of AF by 28 %

 

*defined as lifetime exposure of 2000 hours or more

# but states that increase is moderate.  Evidence is not robust or consistent and the risk is no higher than non-exercisers.

 

Also, that being a competitive/high level/elite athletes PA still reduces mortality by 15 – 50% and, at worse, is no worse than being sedentary.

 

Various other studies suggest a slight increase in AF with intense physical activity for men, but a significant drop in Af risk in women. Or as one put it “non-significant trend towards lower AF with physical activity – risk of AF greater in males”

 

5.       Karjalainen et al 1998

Looked at 300 orienteers (all men).

Risk of mortality                           1.7%                      general population          8.5%

CHD                                              2.7%                                                                7.5%

Afib with no risk factors                 5.3%                                                                0.9%

Afib with risk factors                     12.0 %                                                            9%

 

6.       Elosua et al 2005 “Sport practice and risk of Lone AFib”

Looked at 160 men. 

 

PA                          31%        AF                           control                  14%

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Based on 1500 lifetime hours:                    2.87 x the risk. 

There was a later correction to this report which I was not able to access.

 

Various other studies were bandied about which showed the following increase in risk with high PA

10%        cyclists

3 x          competitive sport

1.8 x      endurance athletes

8.8 x      marathon runners

15 x        physicians

 

7.       Aizer et al 2009 “Relationship of vigorous exercise to risk of Afib”

This study concluded that people doing more PA were younger, drank more alcohol, took more multivitamin, Vitamin E and C supplements, had lower BMI, less hypertension, less likely to smoke and less diabetes.  Also, lower Coronary heart disease and mortality but more AFib, but that in older men the disadvantages were offset by the health gains.  They also only found this link with jogging not any other sport. Jogging more than 4 miles showed an increase of 53% in Afib risk.

 

They also quantified the amount of exercise they were talking about:

Up to one day per week                -9% Risk of Afib

1-2 days                                               +9%

3-4 days                                               +4% (yes, lower than the 1-2 days figure)

5-7 days                                               +20%

All these increases were described as modest.  The average amount of exercise per week was 108 mins and the level was “vigorous enough to work up a sweat”.

 

8.       The Harvard Study (started in 1986)

Those expending 3500 calories per week on exercise were 54% LESS likely to get Afib

Those expending more than 3500 calories per week were 38% LESS likely to get Afib

3500 calories is roughly running 35 miles per week or equivalent.

 

9.       O’Keefe et al “Reverse J Curve” article (not a study)

This looked at lots of other articles and studies and repeated the 2000 hours lifetime exposure figure and added a figure of 20 years for risk. 

They concluded:

5 METS per week             reduced risk of Afib

20 METS per week          maximum benefits

55 METS per week          (about 10 hours of vigorous exercise).  At this level risks outweigh benefits.

They stated that cyclists had a five-fold increase in risk! But their conclusion was “current data is not strong enough to recommend recreational athletes lower their exercise dose especially if it improves quality of life or is needed for performance as risk are moderate.  But less is safer.”

 

10.   Eijsvogels et al 2018 “Extreme Exercise hypothesis”

Concluded that increased fitness led to decreased Afib.

 

11.   N A Mark Estes et al 2017 “Afib in athletes – a lesson in virtue”

Concluded that some studies show Afib is decreased, others show an increase.

They repeated the claim that:

Moderate PA     decreases Afib by 19% in men (8.6 % in women)

Vigorous PA        increased the risk of Afib threefold (but decreased it 28% in women)

 

12.   Neilson et al 2013 “Relationship between PA and Afib”

Again, looking at several studies which showed that PA either increase risk 5.3-fold; 3.1-fold OR decreased it by 11%!  They concluded that “active lifestyle with high or moderate PA seems beneficial and is associated with a significantly reduced risk of Afib”.

 

13.   Everett et al

States that 7.5 MET hours per week in women reduces Afib.

 

14.   ChunShing Kwok et al “Physical Activity and Afib”

Concluded “No significant increase in Afib with higher levels of PA”.  They stated that “studies of athletes with a history of sport were of poor methodology quality and showed a borderline significant association”.  They quoted the risk as between -5% and +98%.

 

15.   Goodman et al 2018 “Excessive Exercise in endurance athletes”

Concluded “Based on risk-benefit evidence it is premature to suggest excessive exercise is unsafe or should be curtained”

 

16.   Sanghamitra Mohanty et al 2016 “Differential association of exercise intensity with risk of Afib in men and women!

Meta-analysis. 

Moderate PA                     women                reduces AFib by 8.6%      men       reduces Afib by 18%

Intense PA                          women                reduces Afib by 28%        men       increases Afib three-fold

 

17.   Brunetti et al 2016 “Incidence of Afib is associated with age and gender in subjects practicing PA”

This meta-analysis and meta-regression analysis states that male only studies show a 7-fold increase in Afib (5-fold increase in under 54 years old) but in mixed sex studies a decrease of 11% (decrease 16% under 54s).  ((This would be the sex specific difference that most studies show where women don’t seem to get as much Afib))

 

They concluded “There was a non-significant trend towards lower AFib in subjects who did PA. Risk higher in males” but claimed the risk of Afib over age 54 are outweighed by the benefits of vigorous exercise.

 

18.   D’Ascenzi et al 2015 “Controversial relationship between exercise and Afib”

States that Afib in common in general population AND in competitive athletes.  It is preventable by regular exercise.  There are no known causal factors but plenty of vague speculation.  Factors such as atrial ectopy, increased vagal tone, changes in electrolytes, Left atrium dilation and fibrosis have all been suggested but there is no convincing data for these.

 

19.   Mont, Sambola et al 2002 “long lasting sport and Lone Afib”

This study looked at 1160 Afib patients in A and E.  70 of these were sportsmen (no women).  ((Incidentally a rate of only 6%!)) Of the non-sporting population with Afib (1090 of them) 50 % were women.  However, they decided to exclude women from their study.

They then concluded that sportsmen tended to get earlier onset Vagal Afib but had lower blood pressure.  They stated that the risk in those who did PA was 63% vs 15% generally.

 

 

20.   Pietro Delise et al 2012 “Sport increases Afib in middle-aged men?”

They looked at studies, analyses, reviews articles and meta-analyses.

They concluded that PA in middle aged men was less than 0.5% per year and possibly linked to vigorous endurance sport.  They stated that there was no convincing data that sport lead to Afib.  The beneficial effects of exercise offset the risk, which, despite the increase, is LOW.  Most studies were weakly suggestive and with no objective evidence.

 

21.   Albrecht et al 2018 Physical Activity types and Afib risk in middle-aged and elderly”

This states “no association between total PA and Afib”.  It said high PA lowers risk of Afib 29%. “PA not associated with higher or lower risk of Afib in older adults”

 

22.   Morseth et al 2016 “PA, Afib and Resting Heart Rate”

They reported on the J curve of increasing Afib with increasing exercise and stated that moderate exercise reduced Afib, but that a lower resting heart rate increased Afib.

 

23.   Choi et al “independent effect of PA and RHR on incident of AF in general population”

Also said moderate exercise decreased Afib.  Lower RHR increased Afib.

 

And finally, here’s Morseth again.  This was one of the last studies I found and I wish I had found it first as it drew virtually all the other studies together in one huge study…

 

24. Morseth et al 2018 “The ambiguity of PA, exercise and Afib”

For elite sport they found increased Afib of between 10% - 30% (men only studies) and between 0% - 1% in mixed studies.  Some of the studies were tiny though and there were no all-female studies.

For non-elite sport they found increases for men of 12.8%-to-8.8-fold increase!  And, in the only female-only study I ever saw, a 40-year practise of ((non-elite)) sport led to a 2.18-fold increase for women.  The authors pointed out that studies showed that the risk of Afib in the high PA group vs sedentary varied from a 40% reduction to a 300% increase!

 

They concluded that PA is on the famous J curve.  The J curve is an illustration that more and more PA is good for you up to a point where it then becomes a risk factor.

Also, they stated that all the studies had limitations:

·         that evidence was weak

·         athletes are more aware of their bodies and so more likely to get diagnosed

·         no confounders were taken into account

·         not many studies included women

They summed up as follows:

·         For the general population, their summary was that ALL studies showed increase physical activity led to decreased Afib even at the highest levels of PA.

·         NO studies show increased Afib with low to moderate amount of PA

·         MOST ATHLETES (90%) DO NOT GET AFIB.

 

Some terminology

PA                                          Physical Activity

Afib                                       Atrial Fibrillation (no distinction made between that and Atrial flutter in these studies that I could see)

RHR                                       Resting Heart Rate

Significant                          Statistically, it means it is unlikely to be caused by chance

Non-significant                 Could be caused by chance

Three-fold                          a 300% increase

Confounders                     Something that influences the effect (PA)and the outcome (Afib) and can lead to them being falsely associated. 

Selection bias                    Where there is a difference between those being studied and those being compared other than what is being studied, that is, they are not randomly chosen 

Publication bias                Where certain studies are not published due to results being the same or ‘uninteresting’.

Control group                    A group who not exposed to what is being studied i.e., in this case, sedentary folk.

J curve                                  A graph illustrating the idea that there is point at which getting fitter, in this example, decreases health rather than increases it.

(( xxx ))                                 my comments.

 

Problems with all these studies:

Ø  many of these studies were meta-analysing and studying each other!  Most notably in the figure of a 28% reduction for women which came up three times.  So obviously circular reporting.

Ø  Each meta-analysis is only as good as the data in the original report so if that showed biases or other problems that will be replicated in the meta-analysis.  What researchers refer to as “garbage in, garbage out”!

Ø  Data was limited in many of these studies (15 people in one). 

Ø  Many showed selection bias. 

Ø  Levels of PA are self-reported and so unreliable

Ø  No confounders were studied.

Ø  Few definitions of what constitutes of high, intense or vigorous PA!

Ø  They contradict each other! Results vary wildly, which suggests no consensus.

Ø  Even the experts cannot agree on what these results mean.

Ø  Few studied women.  Those that did showed no risk for women but, obviously, women have been less represented in sport/intense PA until quite recently and are still present in much smaller numbers in many sports.  So, it is possible that this has not shown in the studies yet.

Ø  The risk to elite sportspeople also has to consider the use of illegal performance enhancing drugs many of which would affect the heart.

 

What do I think?

 

So, on average there was a 1.60-fold increase in risk of Afib (i.e., for every 10 people who get Afib and are not sporty, 16 sporty types get it), but this was only 16% increase for women (so 100 vs 116).  But these estimates varied wildly from -40% to +1500%!!!  For women the risk was from -28% to +200%.  But remember the circular reporting problem where the same stats are used more than once.

 

I think there is an element of selection bias in some of the reports i.e., cardiologists notice fit people with heart problems more!  Most athletes do NOT get Afib and, therefore, there is possibly a genetic disposition for those who do get it – but how do we know whether they would have got it anyway?

 

It seems possible that many decades of ‘eye-balls out’ training could affect the heart and so it probably would make sense from a cardiac point-of-view to have a ‘down’ season, as most elites do anyway, where exercise is reduced a lot or replaced with gentler activities like non-competitive water activities or walking or cycle touring during that time.  This should perhaps be as much as 1-2 months in those who train very hard.

 

One study I saw, not included because it was on a different issue, stated that they had found no mechanism for why exercise should affect the heart despite many speculative ideas as mentioned in study no.18 by D’Ascenzi et al 2015.

 

Overall, the data shows that, even if the risk of Afib is increased, the risk of mortality is still reduced and, obviously, the quality of life is enhanced by the other physical health benefits (generally there are less cancers, less diabetes, less coronary heart disease, less obesity, better diet and lifestyle etc etc) plus mental health benefits AND the pure enjoyment.

 

As a point of interest while the doctors blamed my fitness initially for Afib they changed their mind when they realised how little I really did and I now have ELEVEN different possible causes/triggers for my episodes of Afib: a genetic disorder of the blood vessels leading to strain on the heart and/or anaemia; under-active thyroid leading to sometimes high levels of thyroid activity due to over-medication; a (prescription) drug I once took; PA; menopause; genetics; dehydration; Astra-Zeneca Covid-19 vaccine and being tall (yes, that seriously is stated as a risk factor!)

 

If you are interested in seeing more detail, you could do a lot worse than read the report number 24: “The ambiguity of PA, exercise and Afib” by Morseth et al 2018 which, as stated, looks at many of these reports and has some nice graphs too.

 

Thanks for reading and I hoped it helped (though I know it provided no real clarity!)

Happy Research!