How We Are Measuring "Better"
Almost everything below is measured the same way, so it is worth one paragraph of explanation before the numbers arrive.
Flow-mediated dilation is the standard test. A cuff briefly halts blood flow in the arm; when it is released, ultrasound measures how much the artery widens in response to the rush. A healthy lining widens more. Results are given in percentage points — so "+2 points" means the artery opened 2 per cent wider than it did before.
From the previous article: each extra 1 per cent of widening is associated with roughly 8 per cent lower cardiovascular risk. That gives the numbers below a rough sense of scale.
Flow-mediated dilation is a surrogate marker. We know that people who naturally have better readings go on to have fewer heart attacks. We cannot assume that pushing someone's reading up by 2 points delivers exactly the same benefit as having been 2 points better all along.
The interventions at the top of this table happen to have outcome evidence of their own, which is why they are at the top. Read the numbers as a guide to the size of the biological effect, not as a promise about your own risk.
The Ranking
| Intervention | Measured effect | Evidence |
|---|---|---|
| Aerobic + resistance exercise | FMD +2.49 points (1.17–3.81) in type 2 diabetes | Strong |
| Cocoa flavanols | FMD +1.17 points (0.76–1.57); up to 2.5–3 at the optimal dose | Strong |
| Aerobic exercise alone | FMD +1.21 points (0.23–2.19) | Strong |
| Dietary weight loss | Endothelial markers SMD 0.65 (0.49–0.81) | Moderate |
| Stopping smoking | Smokers sit 3.15 points lower than non-smokers; reversible | Moderate |
| Nitrate-rich vegetables | FMD +0.30 points per mmol; blood pressure falls too | Moderate |
| Resistance training alone | FMD +1.60 points, but the range crosses zero | Mixed |
| L-arginine supplements | Mechanistically logical, disappointing in trials | Weak |
| Oral BH4 or folic acid | Works intravenously; mixed to no effect as a pill | Weak |
| Capsaicin for blood pressure | +0.43 mmHg (−1.15 to 2.01) — no effect | Weak |
Now the detail, because several of these rows have a twist in them.
Exercise: The Unsellable Winner
Pooling trials in people with type 2 diabetes, exercise improved flow-mediated dilation by 1.77 points overall. Split by type, a clear pattern appears.
- Combined aerobic exercise and resistance training: +2.49 points (1.17–3.81) — the best result in the analysis
- Aerobic alone: +1.21 points (0.23–2.19) — solid
- Resistance alone: +1.60 points (−0.52 to 3.72) — the range crosses zero, so this one did not reach significance
Note what that last line does not say. It does not say weights are useless. It says the trials were not consistent enough to be sure on their own — and that combining them with aerobic work produced the largest effect of anything measured.
It works faster than you would expect
A separate analysis looked at nitric oxide markers in the blood rather than artery widening. Across ten trials in 265 people, exercise produced a large increase — standardised mean difference 1.82 (1.14–2.49). HIIT did best at 2.55.
The interesting part is the timing. Trials running eight weeks or less showed a larger effect (2.29) than those running longer (1.19).
That is not a sign the benefit fades. Shorter trials tend to be more tightly controlled and to recruit people with more room to improve. But it does mean this is a quick adaptation. You are not being asked to wait a year to change anything.
Something that raises your heart rate and keeps it there, most days — brisk walking counts — plus resistance work twice a week. That combination has the best evidence of anything in this article, and the mechanism is exactly the one from How Your Blood Vessels Decide to Open: faster flow means more drag on the vessel lining, and drag is the signal to make nitric oxide.
One caveat worth knowing: a broader umbrella review found the best exercise type differs by group, with people who have type 2 diabetes responding well to lower-intensity work. If you are starting from a low base, gentler is not a compromise.
Cocoa: The Surprise in Second Place
I did not expect cocoa to rank this high, and the evidence is better than its reputation as a wellness indulgence suggests.
Pooling 15 studies across 18 intervention arms in 730 people, cocoa flavanols improved flow-mediated dilation by 1.17 points (0.76–1.57). At the optimal dose the effect reached 2.5 to 3 points — comparable to exercise.
Most of the effect appears to travel with one compound in particular, epicatechin.
The dose-response is not a straight line. It is an inverted U. Benefit rises to a peak at around 710 mg of total flavanols — or roughly 95 mg of epicatechin — and then declines at higher doses.
That is unusual and it matters. Most supplement marketing assumes more of the active ingredient is better. Here, taking more than the optimal amount moves you back down the curve.
Two things to be clear about before anyone reaches for the chocolate. Ordinary commercial chocolate is not a reliable source — flavanol content varies enormously and processing destroys much of it, with Dutch-processed cocoa particularly depleted. And the trials used measured flavanol doses, not confectionery. The compound has good evidence. A bar of milk chocolate does not inherit it.
Stopping Smoking
Pooling 14 studies, smokers had flow-mediated dilation 3.15 percentage points lower than non-smokers (95% CI −3.84 to −2.46). That is a bigger gap than any intervention here produces in the other direction.
Two honest notes. That figure comes from observational comparisons rather than trials, so some of the gap may reflect other differences between smokers and non-smokers. And it is a comparison between groups, not a measure of what happens when someone quits.
But the reviewers were clear that the damage is dose-dependent and reversible, with studies showing significant improvement in vascular function among people who successfully stop. Of everything in this article, this is the intervention with the largest gap to close.
Weight Loss — With a Genuinely Odd Finding
Across 37 studies in 1,449 people, dietary weight loss improved endothelial function markers with an SMD of 0.65 (0.49–0.81) — a moderate-to-large effect. Adhesion molecules fell, nitric oxide markers rose.
Now the odd part, and it is the most thought-provoking result in this article.
The analysis found no relationship between the amount of weight lost and the degree of endothelial improvement. Nor did it depend on starting BMI or age.
Which raises an obvious possibility: perhaps it is not the weight loss doing the work. Perhaps it is the change in what people are eating — less processed food, more vegetables, less sugar — and the weight loss is simply what happens alongside.
That is a hypothesis, not a finding, and the authors do not claim it. But it fits with everything else here, and it is a comfort to anyone whose weight has stubbornly refused to shift while their diet improved. The vessels may be responding to the food rather than to the scales.
One caution on this row: the heterogeneity was very high, meaning the individual trials disagreed with each other a great deal. The average is real, but it hides a lot of variation.
What Does Not Work
The bottom of the table is worth as much as the top, and there is a pattern to it.
L-arginine. The raw material for nitric oxide, so supplementing it ought to help. It largely does not, because the bottleneck is the enzyme and its condition, not the ingredient.
Oral BH4 and folic acid. Both work when delivered intravenously. Both are inconsistent as pills, because the oxidative stress you are trying to treat destroys the compound before it arrives.
Capsaicin for blood pressure. The clinical trials pool to +0.43 mmHg, with a range straddling zero. Elegant mechanism, no measurable effect in people.
Notice what the failures have in common. Every one of them is an isolated compound in a capsule, chosen because a mechanism said it should work. Every one of the successes changes how the system is running rather than adding an ingredient to it.
What To Actually Do
Stripped of the numbers, the list is short and slightly boring.
Move most days, and lift something twice a week. Biggest effect in the table, works within weeks, costs nothing.
If you smoke, that is the single largest gap you can close. Larger than anything else here can add.
Eat the vegetables with the nitrate in them — beetroot, rocket, spinach, celery — and do not follow them with antiseptic mouthwash.
Improve what you eat, whether or not the weight shifts. The endothelial benefit did not track the scales.
Cocoa is real, at the right dose, from the right source — and more is not better.
Ignore the capsule aisle. Not because supplements are a scam, but because every intervention that reliably worked in this article changed a process, and every one that failed added a substance.
Combined aerobic and resistance exercise has the strongest evidence for improving blood vessel function — about 2.5 percentage points of extra artery widening, with effects appearing inside eight weeks. Cocoa flavanols come a surprising second, though the dose-response is an inverted U, so more is not better. Stopping smoking closes the largest gap of all. Dietary weight loss helps, and curiously the benefit does not depend on how much weight is lost, which hints that the food matters more than the scales. Nitrate-rich vegetables give a real but modest push. Everything that failed was an isolated compound in a capsule, and everything that worked changed how the system runs.