Free radicals and oxidative stress get talked about constantly, almost always to sell something. Here is what can genuinely be measured, what that number means, and — above all — what it does not mean.
Your body produces free radicals all the time, and rightly so: it uses them to fight infection, to signal between cells and to adapt to exercise. They are not a poison that has crept in. They are part of normal function.
At the same time it produces defences — enzymes, vitamins, molecules that neutralise the excess. Health is not about having zero free radicals. It is about the balance between what is produced and what is neutralised.
When that balance tips towards damage in a sustained way, that is what is called oxidative stress. And it can be estimated using indirect markers.
Two determinations are carried out in the consultation, and they always go together, because on their own neither says very much:
FORT — measures the oxidative load: the hydroperoxides circulating in your blood, which are the trace oxidation leaves on fats and proteins. This is the 'wear' side.
FORD — measures your antioxidant capacity: how much defence your plasma has available at that moment. This is the 'shield' side.
From the two, the device calculates a single number: the redox index. It is not a grade for your health. It is the position of a set of scales at one particular moment.
It is done with a drop of blood from the finger, in the consultation itself, and the result comes out in minutes. There is no need for a vein draw or for waiting days.
It is worth being clear about what it is and what it is not: this is a single reading taken in consultation. It is not the full laboratory blood panel — hormones, vitamin D, ferritin — which is requested separately if it is needed.
Because this figure moves. It moves with your last meal, with the exercise you did yesterday, with an infection, with smoking, with how you have slept this week and with any medication you are taking.
That is not a flaw in the test: it is what the test is measuring. But it has a practical consequence worth stating plainly: a single isolated reading says little. What is informative is the same measurement, repeated under the same conditions, compared with yourself over time.
That is why it is taken fasting and at rest. It is not a protocol whim: it is the only thing that makes the second reading comparable with the first.
And there is a threshold, which you will also be told: below a change of around 20 % it cannot be claimed that anything has genuinely moved. Below that, it is the normal variation of the test itself, not your biology.
It tells you how the balance between oxidative load and defence stands in your blood today. And, if you repeat it, it tells you which direction it has moved in.
It does not tell you that you have a disease. It is not a diagnostic test for anything specific: an altered index shows up in very different situations, and also in healthy people who have slept badly or trained hard.
It is not your 'biological age'. There is no equivalence between this number and how old your body is, however often it is sold that way.
It does not predict what will happen to you. It is a photograph, not a forecast.
What it does do is turn a vague conversation — 'I feel tired', 'I want to look after myself' — into something with a starting point and a way of looking at it again later. That is all, and it is already a good deal.
With the same clarity as in the rest of this blog:
Whether measuring this makes sense in your case — and sometimes the honest answer is that it does not — is decided at the assessment, not before.
First, what it is: NAD⁺ is a coenzyme present in every one of your cells, involved in two very basic processes — how the body produces energy and how it repairs its DNA. It is not a vitamin you take with food, and it is not an antioxidant: it is a part of the machinery.
It appears in this article for a simple reason: these days it is impossible to read about oxidative stress without running into it. So it is worth placing it properly.
First and most important: the redox index does not measure NAD⁺. They are two different things and they should not be mixed up.
What does exist is a hypothesis with a biological basis: accumulated oxidative damage to DNA activates repair mechanisms that consume NAD⁺, and that sustained consumption would contribute to its levels falling over the years. It is a coherent, well-argued explanation.
But it is a hypothesis about a general mechanism, not a chain demonstrated in any one person. And with a caveat that the study proposing it underlines itself: that chain only held up in the men in the sample. In women, the authors did not find the same pattern.
Nobody can look at your redox index and deduce your NAD⁺. Anyone who tells you otherwise is embellishing.
That same study is, as it happens, the one behind the sector's most repeated figure. It circulates widely in headline form: 'your NAD⁺ levels drop by 50 % by the age of 40'. It turns up in adverts, in supplement posts and in clinics.
It is worth looking at closely, because it explains rather well how this works.
The work usually cited is by Massudi and colleagues, published in PLoS ONE in 2012. It is a serious study and its finding is real: NAD⁺ declines significantly with age. Now, what that study actually did:
In fact, when other authors have put numbers to that same data, the largest fall does not appear where the advert says it does: it appears between the newborn and the young adult, and from middle age onwards the decline stops being visible. The headline is not a simplification of the study. It is something else.
And there is something more uncomfortable still. The most recent review of this whole field concludes that the supposed consensus that NAD⁺ falls universally with age is not well supported, and that in human blood the published results are openly inconsistent with one another.
None of this means NAD⁺ does not matter with age. It means something duller and more useful: when somebody puts a big number in front of you in an advert, they have almost always lost along the way which tissue it was measured in, in whom, and whether that figure was in the study at all or was added by the advertiser.
Here we would rather measure yours and tell you what it says, even if it is less spectacular than a headline.
It is measured once so you know where you are starting from. A decision is made — if appropriate — about what makes sense to do. And it is measured again after a period, under the same conditions, to see which way it has moved.
How often it is worth repeating depends on your result and your situation, and is decided in consultation. There is no single interval that suits everyone, and be wary of anyone who gives you one before measuring you.
The measurement is not the objective. The objective is that decisions about your health start from a figure of your own, and not from an assumption or a headline.
If you want to know where you are starting from, begin with the medical assessment. And if that assessment concludes that you need nothing, we will tell you that too.
This article is signed by Dr. Mariana Goldstücker, medical registration (colegiada) no. 032892127. This page is for information purposes and does not replace a medical consultation. The assessment is an individual professional evaluation; treatments are determined case by case and do not guarantee results. Your data is processed under GDPR (EU) 2016/679 and the Spanish LOPDGDD.