Longevity Supplements: A Guide to the Evidence

✓Moderate evidence

The longevity supplement market runs on one rhetorical trick: it shows a result from mice and talks about it as though it applied to you. This guide separates the two and puts an explicit evidence level on every compound.

I write this as someone who spent his first two years buying more or less everything he heard about on a podcast. The single biggest improvement came not from discovering a new compound but from getting blood work done and finding my ferritin scraping the bottom of the range.

How do we label evidence levels?

✓✓Strong evidence meta-analyses or replicated human trials.

✓Moderate evidence one good randomised human trial.

~Preliminary research small, mostly observational studies.

🐁Animal studies only animal models only.

⚗Mechanism only mechanism or in vitro work only.

✗Marketing claim a claim with no research behind it.

The scale is applied consistently across the site. The same compound gets different labels for different claims: creatine has strong evidence for muscle strength and preliminary evidence for cognition. The evidence level describes the claim, not the product.

Which longevity supplements have human trials?

Creatine monohydrate

The best-studied supplement on the market, with hundreds of human trials and a safety profile documented better than most over-the-counter drugs. Dose: 3 to 5 g daily, no loading phase, any time of day.

Beyond strength and muscle mass it has data on cognitive function under sleep deprivation. In a trial published in Nutrients, a single dose of creatine reduced the cognitive decline caused by sleep deprivation. That is still one study, so I label this specific effect moderate rather than strong.

Monohydrate is enough. The pricier forms, including HCl and chelates, show no advantage in head-to-head trials and cost several times more.

Omega-3 (EPA and DHA)

Worth it if you eat little fish, which for most Western diets is the rule rather than the exception. Trial doses: 1 to 2 g of combined EPA and DHA per day.

Watch the labels. “1000 mg fish oil” is not the same as 1000 mg of EPA and DHA, and in cheap products the actual fatty acid content can be three times lower. Always read the combined EPA and DHA figure from the ingredient table, not the capsule weight.

Vitamin D, but only for documented deficiency

Supplementing someone with normal 25(OH)D shows no demonstrated longevity benefit. Supplementing a deficiency does. The difference between those two sentences is one blood test.

Above roughly 40 degrees latitude, skin synthesis is effectively zero from October through March. That argues for testing in autumn, not for taking 4000 IU blind all year.

Magnesium

Form matters. Magnesium oxide sits around 4% absorption and mostly acts as a laxative. Glycinate, citrate and malate absorb considerably better.

A 2021 meta-analysis of magnesium for insomnia in older adults found an effect, but it rested on three small, low-quality trials. This is a good example of formally having a meta-analysis while actually having weak evidence. The label “meta-analysis” does not excuse you from reading what is inside it.

Which supplements have evidence only in animals?

NMN and NR raise NAD+ levels in humans, which is documented. Translating that into lifespan is documented in mice. Those are two different sentences, and an entire industry earns its margin on people confusing them.

Spermidine has promising observational data from the Bruneck cohort and solid mechanistic work on autophagy. What is missing is interventional trials with hard endpoints in humans.

Resveratrol is instructive because it completed the full cycle: enthusiasm, heavy investment, clinical trials, disappointment. Worth remembering when the next compound gets the same kind of headlines.

What does a sensible stack cost per month?

The evidence-backed set lands under £45 a month. One tub of NMN typically costs more than all four items in the upper half of the table combined.

How do you read a supplement label?

Three things I check before buying, in this order.

First, the active ingredient content rather than the capsule weight. “Magnesium 500 mg” usually means 500 mg of the compound, not 500 mg of elemental magnesium. Magnesium oxide is about 60% elemental, citrate about 16%, glycinate about 14%. The nutrition table gives the elemental figure, and that is the number you compare across products.

Second, the chemical form. “Magnesium” with no form named on the front of the pack almost always means oxide, because it is the cheapest.

Third, third-party lab testing. In niche categories such as NMN and spermidine, the gap between the label and the contents can be wide, and manufacturers are under no obligation to verify it.

How do you spot marketing without evidence?

A mouse result quoted without the word “mice”. This is the most common trick in the industry, and checking the source tells you who the study was run on.

A proprietary blend, meaning an ingredient list with no doses. If a manufacturer will not say how much of each is in there, usually there is not much.

Stacks with a dozen ingredients. With twelve compounds at once you will never learn which one did anything, and the individual doses are usually below the effective threshold.

An appeal to one name instead of to research. “Dr X’s protocol” is an argument from authority, not evidence.

A promise with no timeframe. An honest description says when to expect an effect and what to do if it does not arrive.

What is the legal status of these supplements by market?

This section gets skipped a lot, and it decides whether you can legally buy a given product at all. Melatonin is sold over the counter in Poland and the United States but requires a prescription at many doses in Germany. NMN has no approved novel food status in the European Union, which means products sold legally in the EU are usually personal imports.

When buying from overseas shops, check not only price but whether the product carries third-party purity testing. In the NMN and spermidine categories, the gap between the label and the contents can be wide.

What I do not know, and what nags me about it

I do not know whether supplementation does anything for longevity in someone without deficiencies. I suspect that in most cases it does not, and I take creatine and omega-3 anyway, because the risk profile is low and the cost is trivial. That is not a consistent position and I am not going to pretend it is.

What also nags me: the best data in this category concerns cheap, boring compounds, while the entire marketing budget goes to expensive, new ones. It is hard to find a cleaner demonstration that research direction in this industry follows margins rather than questions.

In what order would I do this?

Blood work. Then correcting documented deficiencies. Then sleep, because it has the largest effect on everything else and costs nothing. Only then low-risk, low-cost supplements, tested one at a time for two weeks each.

Supplements with uncertain evidence and a high price go last, if at all. Not because they definitely do nothing, but because without the fundamentals in place you would not see their effect anyway.

The specific sequence for sleep is in the sleep protocol, and which hygiene rules to implement first is covered in sleep hygiene.

Where to start

Get blood work before you buy anything. Then, if your goal is sleep, start with the fundamentals in the sleep guide, because no supplement compensates for a bedroom at 24 degrees. A concrete case of a supplement with a decent mechanism and a low cost of entry is covered in glycine for sleep, and the order in which to introduce changes is set out in the sleep protocol.