A hard run sets off a short, normal rise in inflammation markers, and a marathon can keep CRP up for days. Over the long term, regular running is linked to lower inflammation. In 25,438 adults, each weekly hour of running went with 6.6% lower CRP. Trials of running alone are small and mixed.
Why running looks inflammatory up close
Draw blood from a runner during a long, hard effort and one number jumps out. A signaling protein called IL-6 (interleukin-6) can rise as much as 100-fold. That looks bad on paper. Outside of exercise, high IL-6 has been linked to obesity and to the body using insulin poorly.
Here's the twist. During exercise, the IL-6 comes from your working muscles, and it rises at a time when your body is using insulin better, not worse. Scientists call signals like this "myokines": messages your muscles send to the rest of your body.
So the spike is real. It just isn't the slow, steady kind of inflammation that worries doctors. That kind is a low level that stays up for months, and it is a hallmark of heart disease, metabolic disorders and some cancers.
How big is the spike after a marathon?
Big, and it lasts longer than most runners guess. In a study of 20 people who ran a marathon, the race set off what the researchers called "a considerable inflammatory response" right away.
For every hour a week of running, CRP was 6.6% lower.From a 2025 cohort in Prev Med
CRP (C-reactive protein) is a protein your liver makes when inflammation is up, and it is the marker most doctors test. In 86 marathon runners, CRP was still above its pre-race level at every check after the race, out to 144 hours (6 days). A marker of muscle damage took about as long to settle.
Distance matters. Fifteen well-trained athletes ran both a regular marathon and a 130 km ultra-marathon. Right after the ultra, their average CRP was 18.15 mg/L, compared with 5.58 mg/L after the marathon.
That same marathon study of 20 people found a surprise a few days later. Markers of damage to the body's genetic material went down by day 4, which the authors read as a sign of the body adapting.
Does running cause inflammation over the long run?
This is where the story turns. The biggest study of running and inflammation followed health professionals in three large US studies. Among 25,438 people with blood tests, running had the strongest link to a healthier profile of nine activities, ahead of jogging, aerobics and weightlifting.
For every hour a week of running, CRP was 6.6% lower. The link got slightly weaker once body weight was taken into account, but it held. This kind of study shows a link, not proof that running caused the lower CRP.
Trials, where people are assigned to exercise, help fill that gap. A pooled analysis of 14 exercise programs in 1,568 people found that regular endurance exercise lowered GlycA, a newer blood marker of inflammation. Across 32 studies of 1,510 women past menopause, aerobic training lowered IL-6, CRP and TNF-alpha, another inflammation signal.
Where the evidence gets thin
Not every group sees the drop. In 15 studies of 1,160 healthy adults, aerobic exercise lowered TNF-alpha, but CRP and IL-6 did not change in a meaningful way. If your levels start low, there may be less room to fall.
Trials of running alone are small. In a 2026 trial, 40 adults with chronic low back pain were assigned to a run-walk program, 30 minutes three times a week for 12 weeks, or to a waitlist. CRP and TNF-alpha did not change. Their pain still improved, just not through those markers.
In a study of people with depression or anxiety, 96 did 16 weeks of group running therapy and 45 took an antidepressant. Running improved a combined score of metabolic and immune features more than the medicine did. Its inflammation score trended better, though not by a clear margin.
There is a real cost to going very long, too. A pooled analysis of 7 studies found 18% more upper respiratory infections (the nose and throat kind) after a marathon.
What this means for you
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you have heart disease, high blood pressure or diabetes; you get chest pain, dizziness or unusual shortness of breath when you exercise; you have a joint or back problem you are being treated for; or you are new to exercise and plan to train for a long race.
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The bottom line
Up close, running looks inflammatory. IL-6 jumps mid-run, CRP climbs after a marathon, and an ultra pushes it higher still. Step back to months and years, and the trend runs the other way: lower CRP with every weekly hour of running and calmer markers in trial after trial of endurance training. The spike is the workout. The drop is the habit. Lace up for the habit, give your body time to recover from the big days, and let the slow change do its work.
Common questions
Is running anti-inflammatory?
Over time, it looks that way. In 25,438 adults, each weekly hour of running was linked to 6.6% lower CRP. A pooled analysis of 14 endurance programs found regular exercise lowered GlycA, an inflammation marker. In the short term, though, a hard run raises IL-6 and a marathon raises CRP for days.
Does running reduce inflammation?
In some groups, trials say yes. Aerobic training lowered IL-6, CRP and TNF-alpha in women past menopause across 32 studies. In healthy adults, 15 studies found aerobic exercise lowered TNF-alpha but not CRP or IL-6. A 12-week run-walk trial in people with back pain found no change in CRP. So the answer depends on where you start.
Does running help inflammation if I have a health condition?
It depends on the condition. In a 2026 review of 61 meta-analyses, exercise showed a clear trend toward less inflammation in most chronic diseases. But for people with COPD or fibromyalgia, exercise may briefly raise some markers, and the review says caution is warranted. Ask your doctor what fits you.
How long does inflammation last after a marathon?
In 86 marathon runners, CRP was still higher than before the race at every check out to 144 hours (6 days). Longer races push it further: right after a 130 km ultra-marathon, average CRP was about three times higher than after a regular marathon.
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How this article was made
Researched and written from 12 peer-reviewed papers. Our automated check matched every claim against the exact words of its source, confirmed every paper exists in PubMed, and found none retracted. Checked November 1, 2026. Not individually reviewed by a doctor. Photos are illustrative; the people in them are not patients or readers.
Grades run Strong, Moderate, Emerging, Early and Not supported, and the grade decides the words we may use. How we grade evidence · Medical disclaimer
Sources
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