The Proof Gap, No.1: Which Supplements Are Worth Your Money, and Which Are Selling You Hope

The real question is not “does it work.” It is “proven for what.” Here is how I sort the most popular supplements once you ask it properly.

Aug 17, 2026

Welcome to the Journal. This is a free article. New pieces go out free to subscribers first, and land in your inbox the day they publish. After that they move into the members’ archive, so your inbox is the place to read them free. Subscribe below and you will not miss one.

Members get the deep dives as well: the protocols, the doses, the exact how.

A while ago I promised a series called The Proof Gap, where I take the biggest claims in health and sort them into three piles: proven, promising, and oversold. This is the first entry, and I am starting with the one you spend the most money on: supplements.

The global supplement industry passed 180 billion dollars. Most of what it sells has little evidence behind the claims. But sorting supplements into neat piles turns out to be harder than it looks, and the reason why is the most useful idea in this whole piece.

The question that changes everything: proven for what?

Most supplement articles ask “does it work.” That is the wrong question, and it is why they mislead you. The right question is “proven for what, and in whom.”

Vitamin D genuinely works, for correcting a deficiency. That is not the same as saying it lengthens everyone’s life. Omega-3 has strong evidence, for people who eat little oily fish and for specific cardiovascular situations. That is not the same as a universal “heart and brain” booster. The supplement can be proven and the popular claim still oversold, at the same time.

Upgrade to paid

Here is the principle underneath the whole series, and it is worth sitting with:

The strongest evidence in supplementation is usually not for taking more. It is for correcting something that is missing.

Most of the supplements with genuinely strong evidence are strong because they fix a genuine gap: iron for iron deficiency, B12 where it is low, vitamin D where you are deficient, iodine where intake is inadequate. Fill a real hole and the effect is large and well proven. Take the same thing when you are already sufficient, and the evidence mostly evaporates.

red and brown medication pill — Photo by Raimond Klavins on Unsplash

The one elegant exception: creatine

There is a supplement that breaks the rule, and it is the most interesting one on the shelf.

Creatine improves strength and physical performance without you being deficient in anything. You do not need a gap for it to work. That is unusual, and it is why creatine has some of the strongest evidence of any supplement for training outcomes. Its cognitive and healthy-aging benefits are increasingly interesting but less settled: a 2024 meta-analysis found moderate-certainty evidence for memory, and low certainty for attention and other domains, with the clearest effects in older adults and people starting from a low baseline.

So creatine is proven, for strength. Promising, for the brain. Naming which is which is the whole point.

The three piles, once you ask “proven for what”

Science is not three perfectly clean boxes, and pretending it is would be the exact overclaiming this series exists to call out. So some of these sit on a line, and that line is the honest part.

Proven, when indicated: vitamin D (when deficient), omega-3 (low fish intake or specific cardiovascular use), magnesium (when intake or status is inadequate), and the correction classics like iron, B12, and folate when you are low. Creatine stands apart: proven for strength without any deficiency.

Promising: L-theanine (a real short-term attention effect, a more modest stress effect), ashwagandha (signals for stress, but variable products and study quality), collagen (some positive trials, but quality and industry funding weaken the certainty).

Oversold: the daily multivitamin as insurance for a well-fed adult, BCAAs if you already eat enough protein, biotin unless you are deficient, and the long tail of novel longevity compounds where the human outcome data runs far behind the marketing.

The closing principle

For most vitamins and minerals, the strongest case for supplementation is correcting a genuine gap. Fill real holes, based on your own diet and blood work. Add creatine if you train. And let the rest stay on the shelf, because the biggest wins in health, food, movement, muscle, sleep, still do not come in a capsule.

Where this goes deeper

In the members’ piece, Proof Gap No.1, I give you two tables you can save: one sorting each supplement by what the evidence supports, and one that turns it into a simple buy or do-not-buy decision for your own situation.

The full “proven for what” table, supplement by supplement
A “before you spend your money” decision guide
The evidence and effect sizes behind each verdict
How to work out which gaps you personally need to fill

This is the series I promised. Making “proven for what” the defining question is what makes it a scientist’s framework rather than another supplement ranking.

Upgrade to paid

Proof Gap No.1: The Full Supplement Breakdown, With Tables

Dr. Susanna Søberg, Ph.D

2:11 PM

Proof Gap No.1: The Full Supplement Breakdown, With Tables

For members. Thank you for being here. This is the deep dive, with the exact steps, and it exists because you support my work. You can read everything in the archive and the Journal, any time. Enjoy.

Read full story