Longevity After 40: A Better Biomarker Is Not Proof of Slower Aging

A blood test can improve without answering the question that prompted you to take it: will this help me stay healthy for longer?

That gap matters when you are weighing up fibre, vitamin C or NAD+ supplements after 40. Each has been studied in humans. But the studies measured different things, and their findings support different decisions.

What a biomarker can tell you

A biomarker is a measured biological characteristic. It may help identify disease, track a response to treatment or indicate risk. Its usefulness depends on what the measurement has been shown to predict.

Some biomarkers can serve as substitutes for clinical outcomes in specific settings. Researchers call these surrogate endpoints. Yet even a validated surrogate may miss effects that alter an intervention’s overall benefits and harms. The FDA makes this limitation explicit in its guidance on biomarkers and surrogate endpoints, 2018.

The distinction is between evidence that something changed in the body and evidence that people benefited. A trial might demonstrate both. The word “biomarker” alone tells you neither how useful the finding is nor how far you can extend it.

Psyllium: a cholesterol result with a defined scope

There is randomised evidence that psyllium can lower LDL cholesterol.

In a multicentre trial published in 2000, researchers including a University of Kentucky team compared psyllium with a cellulose placebo in adults with elevated cholesterol. Both groups continued the prescribed dietary approach. After roughly six months, LDL cholesterol was 6.7% lower in the psyllium group than in the placebo group. The tested amount was 5.1 grams twice daily, which describes the experiment rather than a personal dosing recommendation. Anderson and colleagues, *American Journal of Clinical Nutrition*, 2000.

The comparison matters. That percentage describes a difference between groups under the trial’s conditions. It is not a promised reduction for everyone who adds fibre to their diet. Nor does the trial establish that every type of fibre has the same effect.

LDL also has an established role in assessing cardiovascular risk. The FDA lists it among accepted surrogate endpoints in its scientific evaluation of health claims, 2009. That gives the cholesterol finding relevance beyond a laboratory change.

The trial did not, however, measure whether participants lived longer. You can take its LDL result seriously while keeping claims about slower ageing outside its conclusions.

Vitamin C: inflammation and cardiovascular events are different outcomes

A small randomised trial involving Universiti Putra Malaysia and Al-Quds University researchers studied 64 adults with obesity and hypertension, diabetes, or both. After eight weeks, vitamin C supplementation reduced the inflammatory markers hs-CRP and IL-6 relative to the control group.

The trial was open-label, and the control group received no supplement. Its results provide preliminary evidence about those markers in that clinical population. They do not establish that vitamin C prevents cardiovascular events. Ellulu and colleagues, 2015.

A much larger trial examined cardiovascular outcomes directly. The Physicians’ Health Study II enrolled 14,641 male physicians aged 50 or older. Over an average eight years, 500 milligrams of vitamin C daily did not significantly reduce major cardiovascular events. Brigham and Women’s Hospital researchers, Sesso and colleagues, *JAMA*, 2008.

These studies used different doses and populations. The larger trial does not erase the smaller trial’s marker changes. Equally, those changes cannot stand in for a demonstrated reduction in disease.

For you as a reader, the relevant question is the outcome you care about. Evidence about inflammation cannot automatically support a claim about heart attacks, skin pigmentation or longevity. Each claim needs evidence that addresses it.

NAD+: a biological response, then a question about function

In a small randomised crossover trial, University of Colorado Boulder researchers found that nicotinamide riboside, a precursor of NAD+, increased NAD+ in blood cells. This demonstrated a biological response to supplementation. It did not establish longer life or preservation of vision. Martens and colleagues, *Nature Communications*, 2018.

Later research offers a functional finding worth following. In the 2024 NICE trial at Northwestern University, 90 people with peripheral artery disease were randomised to nicotinamide riboside, nicotinamide riboside plus resveratrol, or placebo. At six months, the nicotinamide riboside group had a 17.6-metre advantage over placebo in the change in six-minute walking distance.

This was a phase II trial with a deliberately more permissive statistical threshold for detecting a possible benefit. The investigators called for confirmation in a larger study. McDermott and colleagues, *Nature Communications*, 2024.

Walking performance is relevant to patients’ lives. This emerging evidence deserves attention on those terms. It cannot establish a general anti-ageing effect in healthy adults, and the average difference between groups is not a forecast of what an individual would gain.

Bringing the evidence back to your decision

“Clinically studied” leaves several questions unanswered. You still need to know who took part, what they received, what the comparison group received and what changed over the study period.

A useful way to read a paper is to describe its finding in one sentence:

“In these participants, this intervention changed this outcome, compared with this control, over this period.”

Then compare that statement with the product’s promise. If a study measured blood-cell NAD+, a claim about youthful organs needs additional evidence. If it measured walking performance in people with peripheral artery disease, its result needs that population attached to it.

Percentages need context too. Look for the starting values, the comparison group and the size of the change in the original units. A large relative change does not explain its practical importance by itself.

Personal experimentation answers a narrower set of questions. Suppose you change your breakfast to oats and fruit. You can observe whether it fits your routine, how comfortable your digestion feels and whether you are hungry before lunch. These observations may help you decide whether to keep the habit. They cannot establish slower ageing, and the breakfast change does not replicate the psyllium trial.

Changing a diet, supplement and exercise routine together makes any result harder to interpret. Recording what changed, when it changed and any unwanted effects can help, although a personal record still lacks a trial’s control group. If cholesterol is the concern, a clinician can help decide whether repeat testing is useful and interpret it alongside your overall risk.

You do not need to turn every promising finding into a purchase. A study can justify further research without yet justifying a change in your routine.

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