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Sebastian Rushworth MD: “Is intense exercise bad for your heart?” (a critique)

re: atherosclerosis
re: BMJ: “Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis”
re: Magnesium Intake Is Inversely Associated With Coronary Artery Calcification
re: Sebastian Rushworth MD

Real science is never settled, and anyone who has certainty on such things is not qualified to discuss it.

I have engaged in intense exercise for many years, setting aside from my 18-month ordeal, from which I have finally gotten out of the hole. Hopefully no relapse.

I first call-out my potential bias here, including possible triggering for cognitive dissonance. That is, I do not relish hearing that activities I enjoy might be bad for me—I love my cycling, and I love doing double centuries and hard-core bike rides. Assuming I can get back to my prior fitness levels, I hope to get back to double centuries in particular.

Judge for yourself from my critique just how objective I am being, below. But it feels to me that acknowleding my trigger for cognitive dissonance removes the trigger, or most of it (cannot remove all bias!).

But to perhaps skew it in my favor (with more knowledge), I suggest reading this paper for background, which aside from my critique might fuel your skepticism:

BMJ: “Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis” (or ignore my blog post and read only the BMJ paper).

What is “intense exercise”?

What is “intense exercise”? If well-trained, is 70% to 80% of max heart rate “intense”? Is it intense to be able to do that for 10-15 hours continuously, as I have routinely done for 55 double centuries over the year? Almost by definition, “intense” would on the face of it be unsustainable for more than an hour or two. But let’s see what the Mayo Clinic says:

Moderate exercise intensity — Moderate activity feels somewhat hard. Here are clues that your exercise intensity is at a moderate level: Your breathing quickens, but you're not out of breath. You develop a light sweat after about 10 minutes of activity. You can carry on a conversation, but you can't sing

Vigorous exercise intensity — rigorous activity feels challenging. Here are clues that your exercise intensity is at a vigorous level: Your breathing is deep and rapid. You develop a sweat after only a few minutes of activity. You can't say more than a few words without pausing for breath.

I would say that most of my cycling is moderate to moderate+, interspersed with limited periods of vigorous exercise, such as steep climbs. A lot depends on conditions (heat, humidity, dehydration, etc). Also, amount and type of caloric intake during double centuries set against highly accurate Kj output prove-out a steadily increasing aerobic ability over the past decade, that is, body fat as the primary energy source even to 80% of max heart rate and higher. And lab tests with blood draws at age 36 when out of shape put and overweight me into the 99th percentile for 18-year-olds for VO2 Max (a measure of physical potential). So I am far out on the curve, though well short of pro level.

Hence, if the assertions in the article below were/are accurate, I am one of those people well-designed genetically to damage myself by excessive exercise—it feels good and it comes easily.

So with that context: I consider it absurd that 6 METS is “vigorous” activity; when healthy and rested, I expend ~650 to 750 Kj per hour at relative ease, as measured at the crank by my nearly lab-grade SRM power meter. Typical baseline ride is 1050 Kj over 87 minutes (when well trained), a bit higher on vigorous days and as low as 920 Kj on very easy recovery rides. That seems to put me well within the “two hours of moderately intense exercise”, at least by my own subjective judgment.

Dr Rushworth’s post is broken up so that I can comment on each portion.

Sebastian Rushworth MD: “Is intense exercise bad for your heart?”

by Sebastian Rushworth M.D.., 27 October 2021. Emphasis added.

People are well aware of the heart protective effects of exercise, and recommendations that people increase exercise quantity and intensity are common. But as I’ve written about previously, evidence from observational studies suggests that the sweet spot is reached at just 35 minutes of intense exercise per day (or two hours of moderately intense exercise), after which exercise confers no additional health benefit. After an hour of intense exercise, you are actively harming your health.

I would argue that exercise offer far more than cardiac health! But I accept the hypothesis that there may be a “too much” cutoff. But might hard-core athletes who by definition are stressing their bodies far beyond the norm in fact be more at risk for nutritional reasons, e.g., magnesium deficiency (and more). Correlation is not causation, after all, and science lacks any credible evidence as to causation as yet. I cannot see any basis for asserting that exercise in and of itself is the causative factor.

There are plenty of examples of people who were thought to be supremely healthy up to the point they dropped dead of heart disease. One such example is that frequently comes to my mind is Micah True, the ultra-runner and central character in the book “Born to Run”, who died of a heart attack at the age of 58. Another is Bob Harper, the celebrity fitness trainer and host of Biggest Loser, who had a cardiac arrest at the age of 52 (but survived thanks to rapid intervention by bystanders).

Above, this is the logical fallacy of anecdotal reasoning with a measure of confirmation bias, the opposite of science. Where are the rigorous studies supporting this assertion?

It’s not hard to imagine why more is not always better when it comes to intense exercise. During a bout of intense exercise, the systolic blood pressure is often over 200 mmHg, a level that would in other situations immediately result in a person being placed on multiple blood pressure lowering drugs. The strain on the heart leads to increased blood levels of troponins, molecules that normally exist inside heart muscle cells, but which are released when they suffer damage, and which are used clinically as a means to detect heart attacks. And intense exercise increases oxygen needs massively, resulting in a dramatic increase in free radicals. The longer the exercise goes on for, the harder it is for the body to maintain sufficient mechanisms to neutralize the free radicals, and the greater the probability that they will succeed in causing damage.

Above, I’m not into imagination in terms of scientific credibility—good for hypothesizing but not much more.

I don’t know what my blood pressure is while riding a double century, but in recent years, I’ve been able to recover from the hardest double centuries in the country in as little as 48 to 72 hours. That doesn’t suggest much damage and it has always felt muscular, as would be expected. And if my heart rate at the same wattage drops 15 beats or so from winter to spring (always does), it is clear proof of a highly adaptive response. So there is some stress, but the body adjusts for it.

No evidence is cited as to troponin levels in highly-trained athletes or whether this means anything negative (overdiagnosis?). And highly-trained athletes like me have exceptionally high aerobic capacity. What of the rest of the time for positive effecgs when that capacity is far superior to untrained people, might the body benefit in myriad ways, a balancing effect not accounted for? What of the increased blood flow which can heal and flush toxins out of tissues?Dozens of potential benefits are not addressed. There is no balance to the above.

It’s been known for the last decade or so that professional athletes have an increased risk of developing atrial fibrillation, a condition in which the atria of the heart stop contracting synchronously and instead “wobble” in a disorganized manner. Blood clots frequently form in the fibrillating atria, and can travel from there to the brain, causing a stroke – which is why people with atrial fibrillation are usually put on blood thinners. None of this is controversial. What is it about prolonged intense exercise that causes atrial fibrillation? 

Heart muscle damage, which leads to scar tissue, which leads to disorganized pathways for the cell-to-cell signals that cause the heart to contract.

Good questions above. Is there any evidence for “heart muscle damage” as the causative factor for AFIB among pros?

Citing a study with only a 95% confidence interval is out of character for Dr Rushworth, and he has chosen the most cardiac- intense sport of all in cold conditions (cross country skiing). The relative risk is not at all impressive—less than a 2X effect for most things is not very credible, and it is only 1.15 vs 1.69 (1.46X) at a dubious confidence interval.

Athletes of very high performance are a self-selecting group, and maybe only some of them have this issue for specific reasons (diet, genetics, whatever), rather than a general issue. Things like magnesium deficiency could be at work (during or later, including possibly provoking AFIB). I myself am certain that I have experienced magnesium deficiency year after year until 2020, when I learned about it, and finally addressed it with multiple positive outcomes. I have also had irregular heartbeat about ten years ago when in super highly trained condition. So yeah, it can affect the heart. But that is not proof of long-term effects, or even of damage.

Unfortunately it’s not just the heart muscle that gets damaged by too much exercise. The arteries take a hit too. Multiple studies have found that people who engage in a lot of high intensity exercise have an increased risk of having significant coronary artery calcification, even when compared with people who don’t exercise at all. The lowest risk of having significant coronary artery calcification across the studies was found among those who engage in a moderate amount of exercise. The reason this matters is because a higher amount of calcification usually means an increased risk of experiencing a heart attack.

Above, this one hits home, as per the calcium in my heart. But (a big one) I am certain to have experienced magnesium deficiency year after year until 2020, when I first learned about it, and addressed it with multiple positive outcomes. I can say that I had a deficiency with some confidence even in an aborted season because my body soaked up 2000 to 3000mg of MgCl per day (99% absorption) for 3 months. And 1000mg or more for some months after that. Now, fully loaded 18 months later, I’ll get the shits if I try to do that.

Magnesium Intake Is Inversely Associated With Coronary Artery Calcification

Magnesium deficiency relative to calcium leads to calcium coming out of solution in many tissues of the body, not just arteries. Modern foods are woefully short of magnesium and heavy on calcium—the preferred ratio is thought to be around 2:1 and some claim 1:1. But modern diets are more like 15:1 (15X calcium). What happens to all that excess calcium? One hypothesis is that coronary artery calcification (and lots of high blood pressure too!) is really about malnutrition as in deficiency of magnesium (Vitamin K2 matters also), all being unbalanced with respect to calcium? Medical science has largely ignored such relationships when exploring atherosclerosis.

You don’t find what you are not looking for. To my knowledge, none of these studies cited buy Dr Rushworth have any data at all on body stores of magnesium (ionized magnesium). The idea that a body can properly maintain and repair itself in the face of nutritional deficits is ludicrous. And even pro athletes have long been unaware of the problems with magnesium deficiency.

And here’s the scientifically-unjustified conclusion (IMO):

What can we conclude? Some exercise is good, a lot of exercise is bad. As mentioned above, the optimal health benefits appear at around 35 minutes of intense exercise per day (or 2 hours of moderately intense exercise, such as walking, if you don’t like getting sweaty).

WIND: I don’t dismiss the hypothesis; I would be foolish not to. And of course I agree with the “some exercise is good” part. But I reject the “lot of exercise is bad” part as having dubious merit, having very weak correlational evidence while ignoring nutritional deficits highly probable to be inherent to the cohort used to justify the claim! That is, magnesium deficiency, which every endurance athlete surely suffers from (without supplementation).

The summary judgment (“After an hour of intense exercise, you are actively harming your health”) has extremely weak scientific justification. Dr Rushworth frequently criticizes observational studies, yet here he uses them here for that judgment (“observational”, “not randomized”, “lot of scope for confounding effects”)—and with only a 95% confidence interval. Observational studies are unpersuasive to begin with and they average-out things don’t tell you much of anything about individuals, any more than the pseudo-science of BMI.

Most troubling (seemingly a lack of insight/balance) is that Dr Rushworth does not mention the public health crisis of magnesium deficiency as a factor, and perhaps the main factor. And why would athletes who put their bodies under great stress not be at even more risk for this one nutritional reason alone? Correlation is not causation. But the BMJ article does speak to causation in myriad ways.

BMJ: “Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis”

Also, the analysis fails to include numerous benefits, including but not limited to feel-good ones (quality of life, functionality, etc). When I am in peak shape, I feel better than at any other time. I cannot believe that feeling is disassociated with health, and feeling good is surely a major metric of wellness.

Dr Rushworth replies:

Thanks for the interesting critique. I’m impressed at how quickly you put it together, and many of your points are valid.

As to atrial fibrillation in professional athletes – I chose a study more or less at random. There are in fact many studies that confirm this association.

It’s true that most of the evidence in this sphere is observational, and that’s unlikely to change – it’s hard to randomize people to lots of exercise, some exercise, or no exercise and then follow them for a decade to see what differences there are in cardiovascular outcomes. But in general the observational nature of the data should decrease differences, not increase them, since endurance athletes are on the whole more conscious about what they eat, less likely to smoke, less likely to consume excessive alcohol, and so on. 

Is there evidence that endurance athletes who supplement magnesium have less cardiovascular issues?

WIND: <responseBegin> once I fixed my electrolyte intake for double centuries, all my gastro and appetite and fatigue issues disappeared and never returned. I attribute that to Mg in particular. But that doesn't speak to cardio issues.

I wish there were even one study on Mg in elite athletes, but I've never seen that investigated (could've missed it). Basic chemistry suggests a possible benefit, as Ca likes to precipitate without Mg; the cellular balance being critical. I was hoping to get some evidence for myself via CT heart calcium score progression (or not) following MgCl supplementation, but an 18 month recovery after COVID wrecked those plans, and the experiment.

Magnesium is a prolific area of research in general, but most of it is using nearly useless MgO, along with serum magnesium tests (highly unreliable) instead of ionized magnesium in tissues. MgCl is the only reliable form of supplementation, with nearly 100% absorbed and no diarrhea, so you could do studies that have credible data on actual amount of intake. But no one does that, which is crazy. I've taken as much as 4000mg MgCl in a day without diarrhea; if body stores are low no problem, but if topped-up (months later), then that amount is best for toilet training. Try that any time with Mg citrate of only 1000mg (nominal) and you'll curse supply chain woes.

Research on elite athletes is scattershot in all areas, let alone the Mg thing. My cardiologist friends find it all pretty sketchy to conclude much about elite athletes.

What is clear to me personally is that training of up to 13000 KCal per week (8000 KCal average) draws down all sorts of electrolytes (K, I, Mg, etc), and it's not feasible to eat enough food to replace Mg in particular, and often iodine. After some months, body stores of Mg necessarily plummet, hence the "June problem" after 6 months of training and competing.

My hope is that restoring Mg levels to "topped off" levels in body tissue will halt further accrual of calcium deposits in my heart. But at this point, I have only a hypothesis, and not even anecdotal personal data as per my intro above.<responseEnd>


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