Can magnesium or NAC protect your ears from noise? What the military trials found
A guy who runs the saw at the lumber yard told me he takes magnesium "for his ears." I figured it was the kind of thing you hear at a lumber yard. Then I looked it up, and it turns out the military has been testing pills to protect hearing from gunfire for decades. Some of it is real research, with real results, and some of it is a lot more mixed than the supplement ads let on.
These are the two trials I found most useful, and what I took from them as someone who runs loud machines for a living.
Why anyone thought a pill could help
Loud noise doesn't only shake the tiny hair cells in the inner ear too hard. It also sets off a chemical chain reaction inside them, with oxidative stress and changes in blood flow, that keeps doing damage for hours afterward. The NIDCD's page on noise-induced hearing loss describes the basic damage. The idea behind these trials is that if you can blunt that chemical part, some hair cells survive that otherwise wouldn't.
The magnesium trial: 300 recruits
In the early 1990s, researchers in Israel ran a double-blind trial with 300 young military recruits going through two months of basic training. Training meant repeated exposure to loud impulse noise from weapons, with earplugs on. Every day, half the recruits got a drink with 167 mg of magnesium aspartate. The other half got an identical drink without the magnesium.
At the end, permanent hearing threshold shifts, the lasting kind of damage, were significantly more common and more severe in the placebo group, especially damage in both ears. The less magnesium a recruit had in his blood cells, the more damage he tended to have. And the daily magnesium didn't cause any notable side effects.
That's a strong result for a cheap mineral. It's also one trial, from 1994, in young recruits exposed to gunfire. A 55-year-old cabinetmaker who eats almonds isn't the same subject.
The NAC trial: 566 Marines
NAC, short for N-acetylcysteine, is an antioxidant that helps the body make glutathione. In animal studies it has repeatedly cut noise damage. So the US military tested it in people: a randomized, double-blind trial with 566 Marines during weapons training, 277 on NAC and 289 on placebo.
The main result was a letdown. The overall rate of hearing threshold shifts wasn't significantly different between the groups. But when the researchers looked at the ear closest to the trigger hand, which takes the most noise from a rifle, there was a difference.
Share of Marines whose trigger-hand ear showed a significant threshold shift. A secondary outcome: the trial's main result was not significant.
| Group | Had a threshold shift |
|---|---|
| Placebo (289 Marines) | 35.0% |
| NAC (277 Marines) | 27.1% |
Source: Kopke and colleagues, Hearing Research, 2015.
Side effects were the same in both groups, around 27%. The authors' own conclusion was that the study didn't prove NAC works, but the secondary results were promising enough to keep testing, maybe with better dosing.
Both trials side by side
| Magnesium trial | NAC trial | |
|---|---|---|
| Published | 1994 | 2015 |
| Who | 300 young recruits | 566 Marines |
| Noise | Two months of basic training with weapons | Weapons training |
| Daily dose | 167 mg magnesium aspartate in a drink | NAC (dose in the paper) |
| Hearing protection | Earplugs during training | Trained under a military hearing conservation program |
| Main result | Less permanent damage with magnesium | No significant difference overall |
| Other findings | More damage with lower magnesium in blood cells | Fewer shifts in the trigger-hand ear with NAC |
| Side effects | None notable | Same as placebo |
What I take from it
Three things.
First, both trials were about prevention. They gave the pill before and during the noise, to people with healthy hearing. Neither one shows a supplement can bring back hearing you've already lost. My high-frequency loss isn't coming back, and no capsule will change that.
Second, these people weren't unprotected. The recruits wore earplugs, and the Marines trained under a military hearing conservation program. The supplement was an extra on top, not a replacement. If anything, these studies are a reminder of how much damage gets through even with plugs in.
Third, magnesium is cheap, and most people would do well to get enough of it anyway. The NIH Office of Dietary Supplements' magnesium fact sheet puts the recommended amount at 400 to 420 mg a day for men and 310 to 320 mg for women, and lists legumes, nuts, seeds, whole grains and leafy greens as good sources. It also sets an upper limit of 350 mg a day from supplements for adults, because high doses can cause diarrhea, nausea and cramps. Magnesium from food doesn't count toward that limit. I eat a handful of almonds at lunch now and more beans than I used to. That's about as far as I've gone.
Where hearing supplements come in
The hearing supplements sold online mostly lean on the antioxidant idea, using plant extracts rather than magnesium or NAC. If you're curious how one of them stacks up, here's a breakdown of the antioxidant ingredients in Audifort, a liquid formula with grape seed, green tea and ginseng in its blend. It doesn't contain magnesium or NAC, so it's a different approach from the two trials above, and its antioxidant evidence is mostly from lab work so far.
For the bigger picture on where magnesium and antioxidants stand next to ginkgo, zinc and B12, that summary is fair about what has evidence and what doesn't.
Questions I get at the lumber yard
Should I take magnesium before a loud job? The recruits took it every day for two months, not before a single exposure. Nothing here tells you a dose before one loud afternoon does anything. Eating enough of it every day is the more sensible reading of the trial.
Can I buy NAC? It's sold as a supplement, but the Marine trial didn't prove it works, and the dose that might help isn't settled. I'd wait for better trials.
Will any of this help my ringing ears? These trials measured hearing thresholds, not tinnitus. They don't answer that question either way, so be wary of anyone who says they do.
My shop rule, revised
Plugs and muffs first, every time, no matter what's in the vitamin cabinet. Then eat like someone who wants to keep their hearing: enough magnesium from food, not smoking, keeping blood pressure in check. If a pill ever earns a place in that routine, it'll be on top of the earmuffs, never instead of them. The recruits had earplugs in and still lost hearing. That's the sentence I keep coming back to.