What 72 trials say about cardio and the health of your blood vessels
A new review pooled 72 randomised trials of aerobic exercise and blood vessel function. We explain what was measured, what changed and the caveats.
Most of us know cardio is good for the heart. A review published on 8 October in Sports Medicine – Open looks at one of the ways it helps, inside the blood vessels themselves, and it’s a useful reminder of why steady, regular aerobic exercise earns its place in a weekly plan.
What the researchers looked at
The team, from the University of Ljubljana’s Faculty of Sport, pooled the results of 72 randomised controlled trials involving 3,357 adults. In every trial, one group did a programme of aerobic exercise, such as walking, cycling, running or rowing, and a comparison group didn’t exercise. Programmes lasted between four and 26 weeks, and about two-thirds used continuous training rather than intervals.
The main measure was something called flow-mediated dilation, or FMD. It’s an ultrasound test of the main artery in the upper arm. A cuff briefly restricts blood flow; when it’s released, a healthy artery widens to let the extra blood through. How much it widens says a lot about the health of the endothelium, the thin layer of cells lining your blood vessels. Poor endothelial function is one of the early signs of cardiovascular disease, and FMD is widely used in research because it tends to predict future heart problems.
The participants were a real mix. Seventeen of the trials involved healthy adults; the rest involved people with conditions such as heart disease, diabetes, kidney disease or metabolic syndrome. Ages ranged from about 20 to 78.
What they found
Across the trials, aerobic exercise improved FMD by an average of 2.35 percentage points compared with no exercise. The authors describe that as small but clinically meaningful. Using earlier research that links FMD to future heart problems, they estimate it corresponds to roughly a 24% lower risk of cardiovascular disease.
The exercise groups also saw improvements in a range of other markers, including blood pressure, fitness (measured as VO2max), body fat, cholesterol and blood sugar control.
The most interesting part is the analysis of why. Trials where people lost more weight and body fat, lowered their blood pressure more, or improved their fitness more tended to show bigger improvements in blood vessel function. In other words, the benefits seem to come as a package: fitter heart and lungs, a bit less body fat and lower blood pressure, all pulling in the same direction.
The caveats
This is a careful review, but a few points are worth keeping in mind:
- The 24% figure is an estimate, not a measured result. None of these trials followed people for long enough to count heart attacks or strokes. The figure is projected from the change in FMD using older research.
- The results varied a lot between trials. The authors found high variation and some signs of publication bias, which can make pooled results look a little rosier. When they adjusted for it, the improvement shrank but remained clear.
- It’s a mixed population. Most participants already had a health condition, so the size of the benefit for a healthy 30-year-old may be different.
- Aerobic exercise alone didn’t build muscle. The review found no change in muscle mass, which is why strength training still matters.
What it means for your training
The practical message is reassuringly ordinary. The NHS recommends adults do at least 150 minutes of moderate activity a week, or 75 minutes of vigorous activity, plus strength exercises on at least two days. This review adds more evidence that the aerobic part of that advice changes things you can’t see in the mirror.
You don’t need to run marathons. Brisk walking, cycling, swimming, rowing or a dance class all count. A simple way to judge moderate intensity is the talk test: you can still talk, but you couldn’t sing.
If you already lift weights, adding two or three cardio sessions a week is a good complement. If you’re starting from scratch, begin with short walks and build up gradually. And if you have a heart condition or another health problem, check with your GP before increasing how hard you exercise.
This post is general information, not medical advice. If you have a health condition or concerns, speak to your GP or another qualified professional before changing how you eat or exercise. Read our health and fitness disclaimer.
