A study just published reveals a startling relationship that's the opposite of what most assume. It found that the most heavily trained athletes were almost six times more likely to have plaque in their arteries than those who trained the least [1].
This isn't the story we'd expect. But what does it actually mean? Is exercise now bad for heart health?
Table of Contents
The Puzzle
To answer that question, we need to go back to 2008, when German researchers examined 108 apparently healthy marathon runners. These were men over 50 who had completed at least five marathons in the previous 3 years. The researchers found something completely unexpected [2].
They compared this group with another group selected to have the same heart disease risk profile. In other words, the groups were the same in all relevant ways — except for running marathons. But the marathon runners actually had a higher amount of hard, calcified plaque buildup in their arteries [2].
The study authors concluded we've been making an unwarranted assumption — that being a marathon runner means healthier arteries. The numbers indicated the opposite might be true [2].
Subsequent studies confirmed the signal. In 2017, two landmark papers were published back-to-back in Circulation. One found elevated plaque in UK masters endurance athletes despite low traditional risk factors [3].
Another looked at lifelong exercise volumes in active men around 55 years old. 77% of those with the highest weekly exercise volume had plaque in their arteries, compared to 56% in those with the lowest volume [4].
But there was a silver lining. Researchers noticed the kind of plaque present varied between more and less active groups. The more active group's plaque tended to be calcified. This type of plaque is more stable. It's less likely to rupture and cause serious problems [4].
Then in 2023, the Master@Heart consortium — the same Belgian group behind the new paper — published the most comprehensive study to date. It included 191 lifelong endurance athletes, 191 late-onset athletes, and 176 active but non-athletic controls, all screened to exclude cardiovascular risk factors [5].
Partly, what they found was by now expected. Lifelong endurance athletes had significantly more plaque in their arteries [5].
But then there was a bombshell. Unlike the findings from the previous study, there was no silver lining. Troublingly, the lifelong endurance athletes didn't have a less risky form of plaque than healthy non-athletes. Lifelong endurance sport participation was not associated with a more favourable coronary plaque composition compared to a healthy lifestyle [5].
The Measurement Problem
What's going on here? Why should endurance athletes accumulate more plaque in their arteries? And are they at higher risk of heart attacks?
Lying at the center of this puzzle has been a heated debate. Is it a matter of pure training volume? Do we increase plaque when we log too many cumulative hours on the bike or road over a lifetime? Or is the intensity level the key factor? Do we increase our risk when we're doing lots of exercise at a high level of exertion?
The evidence has been ambiguous. Both sides have been able to make a case for their position.
But there's been a weak point in the evidence. Almost all prior studies relied on self-reported training data. Participants were asked to recall their exercise patterns, and then researchers turned this into metrics like MET-minutes a week. We get these by multiplying activity intensity by activity time. The end result looks satisfyingly precise. But in most of these studies, it's a metric based on surveys and memory, not actual measurements. And we've found recall data doesn't correlate with actual measurements of activity very well [1].
This new study did something different. It tracked participants using wearable monitors — in addition to gathering the usual self-reported data. In this observational, cross-sectional analysis of the Master@Heart study, 222 males (median age 54 years) were included: 77 lifelong athletes, 98 late-onset athletes, and 47 controls. Training load was assessed using objective wearable-derived training duration and intensity over 12 consecutive months [1].
Researchers calculated training load by multiplying training duration by the level of intensity, measured by heart rate [1].
And that's how they derived the shocking number. Those with the highest training loads had almost 6 times the risk of plaque [1].
Interestingly, when they looked at the same participants using conventional self-reported data — the old method — the association essentially vanished. MET-minutes per week based on self-reported training load was not associated with coronary artery disease [1]. This shows how significant the choice of measurement method can be.
So what does this study tell us about the debate? Is intensity or volume the main driver of increased plaque? The answer suggested by the study is that it's a combination. High-intensity exercise alone, without lots of volume, wasn't linked to higher levels of plaque. And high volume showed a stronger connection with plaque when it included a large amount of high-intensity training [1].
What the Data Actually Shows
But what does this actually tell us? Is a high exercise volume — especially combined with high intensity — dangerous for heart health? The answer is nuanced.
First, it's important to notice that this study found more plaque. But, it did not find more heart attacks. The plaque in the athletes' arteries was found because they were looking for it using a CT scanner. It wasn't causing any obvious symptoms or problems. There's no data here showing that the athletes doing the most training were having more heart attacks.
Second, it's important to keep in mind who we're comparing the most active athletes to. The comparison group isn't couch potatoes. They were moderately active. Sedentary individuals and those with traditional cardiovascular risk factors were not represented in this study [1].
So we're looking at a set of people within this study who are all in relatively good shape. The study doesn't tell us about how athletes at the high end of the intensity and volume spectrum compare to people who aren't active. That would surely give us a very different picture. We'd expect sedentary individuals to have far worse outcomes.
But let's return to the first point. This study found more plaque with high-volume athletes. But it didn't find worse health outcomes. And that's really the key thing we want to know. Does the greater plaque burden for the high-volume athletes lead to problems?
To get a better answer to this question, we need to turn to another study. A study with over 21,000 participants, followed for around 17 years, found that high-volume exercisers were more likely to have elevated measures of plaque. That matches the pattern. But — crucially — they were not more likely to die from heart disease or other causes [6].
So far, then, here's what the data seems to be showing. High levels of intense exercise increase plaque formation. But the additional plaque doesn't correlate with increased risk of death from heart attacks or other causes.
But there is a newer study drawing on data from this same group of people. And it complicates this picture slightly. The researchers added a few more years of follow-up. And when they did so, some additional patterns emerged [7].
The numbers for this longer study push back against the idea that plaque found in athletes might be somehow safer than plaque found in less active individuals. The researchers found that the risk of heart disease, given the presence of plaque, was about the same at every activity level. In other words, plaque boosts our risks, whether we're super fit or relatively inactive. And, surprisingly, being in the highest volume exercise group wasn't associated with a lower heart attack risk than being in the lowest-volume group [7].
Rather, there was a sweet spot for heart disease risk that fell in the middle. Those getting at least the recommended amount of 150 minutes a week of moderate exercise or 75 minutes of intense exercise had the lowest risk, compared to those who did less — and those who did a large volume [7].
So does that mean we should just avoid really high volumes of exercise?
Here's the interesting wrinkle. The data did reveal something special about the highest-volume group. Compared to the other groups, they had the lowest risk of death from all causes [7].
So the picture that emerges from all this data is interestingly mixed. High-volume, high-intensity exercise is linked to more plaque, compared to more moderate exercise. And that plaque is associated with heart disease risks when it comes to athletes, just like for everyone else. But when we look at overall health — and overall death rates — there still seems to be an advantage gained by those with very high training volumes. It appears that the downsides to high volume when it comes to heart health are offset by other systemic benefits of exercise.
Practical Takeaways
So let's talk about the practical takeaways. What does all this actually mean for us when it comes to exercise?
Exercise is still the most powerful tool we have for promoting a healthy and long life. There's nothing in the studies we've looked at that overturns that.
And the data reinforces this point: exercise still lowers all-cause mortality. This is a classic case where it's far better to focus on hard outcomes — like heart attacks and deaths — rather than markers like plaque scores.
Equally, however, fitness is not immunity. Even where we're amongst the most active, this doesn't give us blanket protection from heart disease.
If we're in the group of very high-volume athletes, these studies suggest we could still have plaque building up in our arteries. The right response isn't to stop exercising. Rather, it's not to assume that being fit means you don't have to pay attention, or that other interventions to address heart disease risk might not be necessary.
Personally, I exercise because the evidence for its benefits is overwhelming. I also started taking lipid-lowering medications a few years ago, even though I'm only 34 now without any other risk factors. I want to avoid plaque formation as much as possible. Especially with this exercise data. It's not a matter of either-or, but both-and.
I aim to get my LDL-c below 50-60mg/dL due to the PESA study. You can get your own personalized health plan to discuss with your doctor here.
For most, it's a bit of a shock to learn that exercise might have a downside when it comes to blood vessel health. But health is full of surprises like that — which is why it's so important to stay on top of the latest evidence and work with your doctor on a comprehensive approach to heart health.
References
1. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.125.077117
2. https://academic.oup.com/eurheartj/article-abstract/29/15/1903/509365
3. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.116.026964
4. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.117.027834
5. https://academic.oup.com/eurheartj/article/44/26/2388/7069916
6. https://jamanetwork.com/journals/jamacardiology/fullarticle/2722746
7. https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.124.070335
