Biomarkers: The Gap Between Normal and Optimal — Why Standard Ranges Aren't Enough

"Your results are normal." Four words that sound reassuring — and can be deeply misleading.

When your doctor says your blood test is normal, they mean your results fall within the reference range printed on the lab report. That range is usually set to include 95% of the population. It's designed to identify disease. It is not designed to identify optimal health.

These are very different things.

How Standard Reference Ranges Are Set

Clinical reference ranges are calculated statistically. Labs take a large sample of people considered generally healthy, measure a biomarker across the whole group, and define "normal" as the middle 95% of results. The top and bottom 2.5% are flagged as abnormal.

This is a sensible system for disease detection. If your result sits outside 95% of the population, something may be clinically wrong.

But here's the problem: the population used to define "normal" is the modern Western population. A population where roughly 40% of adults are overweight, where metabolic dysfunction is widespread, and where most people will eventually develop at least one chronic disease. When your LDL cholesterol is "normal," it means it's similar to most people in this population — not that it's optimal for living to 90 with a clear mind and a healthy heart.

The average is not the goal. The goal is to live well for a century.

What Longevity Research Actually Shows

Over the past two decades, researchers have studied what biomarker levels are associated with the longest and healthiest lives. The findings consistently point in the same direction: the optimal levels for longevity are significantly better than what standard reference ranges call "normal."

A few examples:

HbA1c (average blood sugar over 3 months): The clinical "normal" threshold is below 48 mmol/mol. Research on centenarians — people who actually reach 100 — consistently shows HbA1c below 36 mmol/mol throughout their lives. A result of 42 mmol/mol is clinically fine. From a longevity perspective, it's a signal worth addressing.

LDL cholesterol: Standard clinical guidance flags LDL above 3.0 mmol/L. Research using Mendelian randomisation — a technique that isolates the causal effect of a biomarker by using natural genetic variation — shows that cardiovascular risk continues to fall at LDL levels well below 2.0 mmol/L. The relationship is roughly linear with no floor. Lower is better, within reason.

Fasting insulin: Most labs don't even test fasting insulin as part of a standard panel. When they do, anything below 25 mIU/L is considered "normal." But research in metabolically healthy populations and centenarian cohorts suggests optimal fasting insulin is below 7 mIU/L. A result of 18 mIU/L is clinically unremarkable — and may reflect years of developing insulin resistance.

Ferritin (iron stores): Standard ranges extend to 300 µg/L for men. Research published in Metallomics found that ferritin levels between 70–79 ng/mL were associated with the lowest mortality and lowest inflammatory markers — in both men and women. The relationship follows a J-shaped curve: risk is high when ferritin is very low, drops rapidly in the 50–100 range, and rises again above 150–200.

This pattern repeats across marker after marker: inflammation, kidney function, glucose metabolism, thyroid function. The research consistently shows a meaningful gap between the population average and what the longest-lived people actually look like.

Two Thresholds, Two Questions

This is why our Biomarkers widget shows two reference lines for every marker — not one.

The clinical range answers the question: Is anything clinically wrong? This is the standard reference range used by labs and doctors. A result outside this range warrants medical attention.

The longevity-optimal target answers a different question: Where do I want to be for the longest, healthiest life? This target is drawn from research on centenarians, Mendelian randomisation studies, and the clinical frameworks of longevity-focused physicians like Peter Attia.

The three zones this creates:

• Optimal (green): Within the longevity-optimal target. This is where you want to be.
• Borderline (amber): Within the normal clinical range — your doctor wouldn't be concerned — but outside the tighter longevity target. Worth monitoring and, where actionable, worth improving.
• Out of range (red): Outside the standard clinical range. This warrants a conversation with a doctor.

When you see "Borderline" on a result, it does not mean your lab made an error or that your GP was wrong. It means your result is clinically normal and there is a meaningful opportunity to optimise it for long-term health.

A Worked Example: Your LDL

Suppose your LDL comes back at 2.7 mmol/L. Your lab report says it's within the reference range. Your GP agrees. Our app says "Borderline."

All three are correct.

Your result of 2.7 is below the clinical threshold of 3.0 mmol/L — so there's no clinical concern. But it's above our longevity target of 1.8 mmol/L. Over decades, LDL above 1.8 contributes to the slow accumulation of arterial plaque — a process that takes 20–30 years to cause problems, and which is largely preventable if addressed early.

This is precisely what longevity medicine is about. Not treating disease. Preventing it, decades before it would otherwise show up.

At 2.7 mmol/L, the first step isn't medication — it's diet (reducing saturated fat, increasing soluble fibre) and exercise (aerobic training reliably lowers LDL). A retest in 6 months will show whether these changes are working. If they do, you've moved the trajectory. If they don't, it's a conversation worth having with your doctor.

What This Means in Practice

Most people who come to this app are not sick. They're trying to stay healthy. Standard reference ranges were not designed for them.

"Normal" was built to catch disease. Our longevity targets are built to support a life that gets to 90 in good shape — cognitively sharp, physically capable, and genuinely well.

The gap between the two is real. Knowing where you sit within that gap — not just on the disease side of the clinical threshold — is genuinely useful information. Not to alarm you. To give you something to work with while you still have decades of compounding in your favour.

A note on confidence: Not every longevity-optimal target has the same quality of evidence behind it. Markers like LDL, ApoB, HbA1c, hsCRP, and eGFR have very strong research support for their longevity targets. Others — like fasting insulin, TSH, and ferritin — are based on well-reasoned functional medicine consensus but should be interpreted with appropriate humility. We note the evidence basis for each marker in the widget and encourage you to discuss any non-optimal results with a doctor before making changes.

We are not doctors. Nothing in this widget or this article is medical advice. It is educational information to support informed conversations with healthcare professionals.

The 100 Great Years perspective

The central promise of 100 Great Years is not to help you avoid dying. It is to help you live fully — with energy, independence, and capability — for as long as possible. Standard medical reference ranges were designed to identify illness in populations where chronic disease is common. They were not designed for the person who wants to reach 90 in genuinely good shape. The longevity-optimal targets in this widget represent a different standard: not "normal for a modern Western adult," but "consistent with the biology of people who actually make it to 100 in good health." That distinction is what this platform is built around.

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This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making decisions about your health.