Twelve weeks in, the magnesium group looked exactly like the placebo group. Nothing had moved. Then researchers measured again at week 24, and the picture changed. That delay is the most interesting part of a 2016 trial on magnesium and arterial stiffness, a proxy for how fast your blood vessels are aging. A larger, newer trial from the same research group complicates the story.
The Study: Small, Controlled, and Carefully Blinded
The paper, published in the American Journal of Clinical Nutrition by Joris and colleagues at Maastricht University, was a 24-week randomized, double-blind, placebo-controlled trial. It enrolled 52 overweight or slightly obese adults: 30 men and 22 postmenopausal women, with an average age of 62 (±6 years).
Participants took either magnesium or placebo capsules three times a day. The magnesium arm received 3 × 117 mg, about 350 mg per day. The abstract does not specify which magnesium compound was used, so we won't guess.
The primary vascular measure was carotid-to-femoral pulse wave velocity (PWVc-f), assessed at baseline, week 12 and week 24. It is widely used as a measure of arterial stiffness. Faster pulse waves mean stiffer arteries, and stiffness tends to rise with age. The team also ran 24-hour urine collections and 24-hour ambulatory blood pressure monitoring at the start and end.
The Striking Result: A 1.0 m/s Drop, but Only at Week 24
The headline numbers:
- Week 12: PWVc-f difference vs. placebo was 0.0 m/s (95% CI −0.6 to 0.5; P = 0.90). No effect.
- Week 24: PWVc-f was improved by 1.0 m/s in the magnesium group vs. placebo (95% CI 0.4 to 1.6; P = 0.001).
So the benefit was not quick. Whatever magnesium did to the vessel wall, it did not show up until the second half of the trial. That fits the idea that vascular stiffness reflects slow structural and functional changes rather than something that flips in a few weeks. The study can't tell us why the effect appeared late, though, and the authors frame the finding as a potential mechanism rather than proof.
What Didn't Change (and Why That Matters)
Two details deserve attention.
Blood pressure didn't move. Neither office nor 24-hour ambulatory blood pressure changed. If magnesium softened arteries here, it apparently did so without the blood pressure drop many people expect. That's interesting, but it also means the result isn't a simple "lower BP" story.
Serum magnesium barely budged. Blood levels only trended upward at 24 weeks (+0.02 mmol/L; 95% CI 0.00 to 0.04; P = 0.09), which did not reach significance. Urinary magnesium excretion did rise by 2.01 mmol per 24 hours (P < 0.001), confirming participants were taking the capsules and absorbing some of the mineral. Serum magnesium is tightly regulated and is a poor window into total body stores, so this isn't surprising, but it does mean we can't tie the vascular effect to a clear blood-level change.
No adverse events were reported.
The Plot Twist: A Bigger Trial Found Nothing
If the story ended here, it would be a tidy longevity hook. It doesn't. A larger follow-up from the same group (Schutten, Joris et al., 2022, Journal of the American Heart Association, PMID 35253448) enrolled 164 overweight or slightly obese adults. It compared magnesium citrate, oxide and sulfate at 450 mg per day against placebo for 24 weeks. It found no significant effect on arterial stiffness or blood pressure.
The two trials differ in dose, formulations and sample size, so they aren't a perfect like-for-like comparison. But the follow-up is larger and tested several forms, and it did not reproduce the 2016 finding. The fair reading is that the original result is a hypothesis-generating signal, not a settled benefit.
Limitations You Should Know About
- Small sample: 52 people is modest, and small trials can overestimate effects.
- Specific population: Overweight or slightly obese adults around age 62. Results may not apply to lean, younger or already-healthy people.
- Surrogate endpoint: PWV is a marker related to cardiovascular risk, not a measure of heart attacks, strokes or lifespan. The trial wasn't designed to show hard outcomes.
- Unreplicated: The larger follow-up did not confirm the effect.
- Unspecified form: The abstract doesn't say which magnesium compound was used.
Practical Takeaways
What was tested: About 350 mg of magnesium per day, split into three doses of roughly 117 mg, for 24 weeks. Any benefit, if real, took the full six months to appear, so short experiments won't tell you much.
Who it might interest: Adults in their 50s and 60s who are overweight and want to support vascular health. Even so, the evidence is mixed, and magnesium is not a substitute for proven approaches such as exercise, weight management, blood pressure control and a diet rich in magnesium-containing foods like legumes, nuts, seeds and leafy greens.
Who should be cautious or skip it: This is general guidance, not a finding from the paper. The kidneys clear excess magnesium, so people with kidney disease should not supplement without medical supervision. Anyone on prescription medication, especially for heart conditions, should check with a clinician or pharmacist first. Higher doses of supplemental magnesium commonly cause digestive upset, and 350 mg per day is also the usual upper limit set for supplemental magnesium in adults in the U.S.
Bottom line: A small, well-run trial saw stiffer arteries get meaningfully less stiff after six months of magnesium, with no blood pressure change and no adverse events. A larger follow-up did not find the same effect. Treat magnesium as an interesting but unproven tool for vascular aging, not a proven fix.
