Supplements — What the Evidence Actually Shows

Walk into any pharmacy or scroll through any wellness platform, and you will encounter hundreds of supplements claiming to support longevity, cognition and metabolic health. There are voices on social media platforms who make completely unsubstantiated claims about supplement benefits, and others who wilfully or deliberately misconstrue weak evidence to sell products. The gap between the marketing and the evidence is, in most cases, substantial.

This is not to say that supplementation is without value. Some supplements have a genuine evidence base. The problem — and the reason I write about this — is distinguishing them from the much larger pool of products with plausible mechanisms but no meaningful human trial data.

The hierarchy of evidence

Before evaluating any supplement claim, I think it is worth understanding what kind of evidence underlies it. In ascending order of reliability:

• In vitro studies (cells in a dish) — informative for mechanism, not clinical outcomes
• Animal studies — useful, but human translation is far from guaranteed
• Observational human studies — show associations, not causation
• Randomised controlled trials — the gold standard, though quality varies enormously
• Meta-analyses of high-quality RCTs — the most reliable basis for recommendations

Most supplement marketing draws on the first two categories. Robust human trial data is the exception, not the rule. When a supplement is sold on the basis of a mouse study or a cell culture experiment, the claim is plausibility — not evidence of human benefit.

Where there is reasonable evidence

A small number of supplements have genuine human evidence behind them, in the right context.

Vitamin D. Deficiency is widespread, particularly among people with limited sun exposure. Supplementation in those who are genuinely deficient has reasonable evidence for musculoskeletal and immune health. The evidence for broader longevity benefits is more contested, and supplementing without checking baseline levels is not well supported.

Omega-3 fatty acids. A complex area. The REDUCE-IT trial showed cardiovascular benefit with high-dose icosapentaenoic acid (EPA) in a specific high-risk population. The evidence for lower-dose fish oil in the general population is more modest.

Creatine monohydrate. Among the most extensively studied supplements in existence. The evidence is strong for supporting muscle protein synthesis, and emerging data suggests potential cognitive benefits in older adults. It is one of the more robustly evidence-backed options available.

Magnesium. Genuine deficiency is common in Western diets. Supplementation in those who are deficient supports sleep quality, muscle function and metabolic health. As with vitamin D, the benefit is concentrated in those who are actually deficient.

This is a short list — and it is short for a reason.

What concerns me

The pattern that concerns me most is the search for a magical pill or solution that avoids the less exciting interventions that actually have evidence — sleep, exercise, blood pressure control, lipid management, weight management, smoking cessation, alcohol reduction. These less glamorous interventions do far more for healthspan than any supplement on the market.

The serial novelty pattern is another red flag. This month it is NMN, next month methylene blue, the week after something else. When a category churns through “breakthroughs” every few weeks, that is a marketing cycle, not a scientific one. These cycles are often driven by influencers looking for clicks.

I am also wary of the dose-dependence problem. Many supplements that are harmless or even helpful at moderate intake are problematic at the doses used in marketing claims. More is not always better, and supplementation in people who are not deficient is rarely useful.

A working framework

Rather than asking “should I take this supplement?”, a more useful question is: “What is my current status, and what does the best available evidence suggest for someone in my situation?”

This is the domain of personalised, evidence-based medicine — assessing individual biomarkers, understanding the quality of the evidence, and making decisions that are proportionate to what that evidence actually supports. It is rarely a simple yes or no.

The bottom line

The good news is that the supplements with real evidence are also the ones with reasonable cost, well-characterised safety, and clear indications. Vitamin D in deficiency, omega-3 in selected high-risk patients, creatine for muscle and possibly cognition, magnesium in deficiency — these are useful tools.

The longevity benefits of most other supplements remain unproven. My priority is always the interventions with the strongest evidence first — the unglamorous ones that move the needle. Supplementation can have a role, but it sits well below the foundations: sleep, exercise, nutrition, blood pressure, lipids, glucose, alcohol, smoking, social engagement and meaningful preventive screening.

Get those right, and the question of whether to add a particular supplement becomes a much smaller one.