We all know about the dangers of high blood sugar and diabetes, but fasting insulin is another important factor in metabolic health. Insulin, essential for life, can become harmful when levels are too high.

Conventional ranges for fasting insulin are too permissive, masking early signs of metabolic dysfunction that could lead to diseases like diabetes, cardiovascular disease, and Alzheimer’s. Based on the latest research, this article explains the optimal range for insulin adopted by Superpower.

Key Points

• Metabolic Disease Detection: High fasting insulin is an early indicator of metabolic dysfunction, often signalling issues before blood sugar levels become abnormal.
• Broader Implication: Beyond blood sugar control, fasting insulin influences cardiovascular, brain, and metabolic health. Emerging evidence also suggests a strong link with cancer risk.
• Optimal Fasting Insulin Range: The lower optimal range is linked to better metabolic health, reduced heart disease risk, and increased longevity.
  • Conventional Range: <25 μIU/mL
  • Optimal Range: 2.6-5 μIU/mL

What is Fasting Insulin?

Insulin is a hormone produced by the pancreas that regulates blood sugar levels and plays key roles in fat and protein metabolism. Think of insulin as a molecular key that unlocks the doors of your cells, allowing sugar to enter. When you eat, especially carbohydrates, your blood sugar levels rise. This signals your pancreas to release insulin, which then facilitates the movement of sugar from your bloodstream into your cells for energy use or storage.

Fasting insulin refers to the level of this hormone in your blood after an 8-12 hour period without food, typically measured in the morning before breakfast. This measurement provides insight into how hard your pancreas must work to maintain steady blood sugar levels when your body isn't actively processing food.

Why should you care about Fasting Insulin?

Fasting insulin is a crucial early indicator of metabolic health, often revealing issues before they manifest as abnormal blood sugar levels or other visible symptoms.

When you are metabolically healthy, your pancreas releases just enough insulin to maintain blood sugar within a tight range. However, when cells become resistant to insulin's signals, the pancreas compensates by producing more insulin, leading to elevated fasting levels. Even levels considered "normal" by conventional standards can indicate the beginnings of insulin resistance, setting the stage for various chronic diseases.

The impact of chronically elevated insulin extends beyond blood sugar control. In the cardiovascular system, high insulin contributes to atherosclerosis by increasing cholesterol synthesis and arterial plaque formation ^{[1, 2]}. Research shows that higher fasting insulin levels are associated increased risk of heart disease and even in non-diabetic individuals ^{[3, 4]}

Insulin's role as a growth factor means elevated levels can potentially stimulate cancer growth ^[5]. Studies have found that higher fasting serum insulin is associated with increased cancer mortality even in individuals without diabetes ^[6-8].

The influence of insulin on brain health is equally significant. Research has linked insulin resistance in the brain to cognitive decline and neurodegenerative disorders ^{[9, 10]}. In fact, the connection with Alzheimer's disease is so strong that some researchers have termed it "Type 3 diabetes" for its association with insulin dysregulation ^[11].

Insulin also plays a crucial role in metabolism and weight management. It promotes fat storage and inhibits fat burning, which can complicate efforts to maintain a healthy weight ^[12]. This effect, combined with insulin's influence on other hormonal systems, can create a cascade of metabolic challenges. Excess insulin interferes with thyroid function, affects fertility, and disturbs the delicate balance of the entire endocrine system ^{[13, 14]}.

Perhaps most crucially, research has demonstrated that higher fasting insulin levels strongly predict the development of type 2 diabetes and metabolic syndrome, even years before diagnosis ^[15-17]. This predictive power makes fasting insulin an invaluable tool for early intervention and prevention.

By monitoring fasting insulin levels and detecting elevations early, you can take proactive steps to prevent or delay the onset of chronic diseases associated with insulin resistance and metabolic dysfunction.

What is the conventional reference range?

The conventional reference range for fasting insulin is typically:

• Normal: less than 25 μIU/mL
• High: Greater than 25 μIU/mL

These ranges are primarily designed to identify overt hyperinsulinemia and other clinical conditions related to extreme insulin elevations. They are not optimized for detecting early stages of insulin resistance or subtle metabolic dysfunctions that may precede clinical disease.

Why is the Conventional Range for Fasting Insulin Problematic?

The conventional fasting insulin range (typically <25 μIU/mL) is problematic as it's designed to diagnosis diabetes rather than preventative healthcare. This approach overlooks the cumulative impact of chronically elevated insulin and allows for higher levels than may be optimal for long-term health.

Research shows that even mild elevations of fasting insulin within the "normal" range can silently contribute to insulin resistance and metabolic syndrome over time ^[18]. The conventional range lacks sensitivity to these early-stage changes, as insulin resistance can develop at levels well below the current threshold. This insensitivity leads to delayed intervention and missed opportunities for prevention. Studies have found:

1. Individuals with fasting insulin in the upper quartile of the normal range were 5-times more likely to 2 diabetes compared to those in the lowest quartile ^[19].
2. Those with fasting insulin levels below 5 μIU/mL had significantly lower risks of cardiovascular disease and all-cause mortality ^{[20, 21]}.
3. Each unit increase in fasting insulin within the normal range is associated with a 5% increase in cardiovascular risk ^{[22, 23]}.

Moreover, in a population where metabolic dysfunction is common, "average" doesn't mean "healthy." This approach risks normalizing suboptimal levels and obscuring early signs of metabolic issues. A 15-year study found that maintaining lower fasting insulin levels throughout adulthood led to better metabolic health in later life ^[24].

By adhering to this broad range, we miss opportunities for early intervention and proactive health management, potentially allowing significant metabolic dysfunction to develop unnoticed.

What is the Superpower Optimal Range for Fasting Insulin?

Superpower recommends a more stringent optimal range for fasting insulin:

• Superpower Optimal Range: 2.6-5 μIU/mL

This range is based on extensive research linking lower fasting insulin levels to improved metabolic health, reduced disease risk, and increased longevity.

Supporting Evidence from Research Studies

Superpower's recommended optimal fasting insulin range of 2.6-5 μIU/mL is backed by extensive research linking lower insulin levels to improved health outcomes and longevity.

Individuals with fasting insulin levels below 5 μIU/mL show significantly better metabolic health, including enhanced insulin sensitivity and reduced risk of metabolic syndrome and diabetes^[15-18]. For every 1 μIU/mL increase above 5 μIU/mL, the risk of type 2 diabetes rises by 5-7%, even within the conventional "normal" range. ^{[26, 33]}

Cardiovascular health is strongly influenced by fasting insulin levels. A large-scale study found that individuals with levels above 15 μIU/mL face a 1.5-fold higher risk of heart failure compared to those below 5 μIU/mL, even after accounting for other risk factors ^[27]. Furthermore, research has shown that elevated fasting insulin is associated with increased arterial stiffness and carotid intima-media thickness, both early markers of atherosclerosis.^{[28, 29]}

The impact of insulin levels extends to cancer risk. Individuals with fasting insulin levels in the highest quartile have a 1.4-fold increased risk of cancer compared to those in the lowest quartile ^[30]. This association is particularly strong for colorectal, pancreatic, and breast cancers. Studies suggest that higher insulin levels can promote cancer growth and inhibit cell-death by activating insulin-dependent pathways ^[30].

Cognitive health also benefits from lower fasting insulin levels. Long-term studies demonstrate that people with lower levels maintain better cognitive performance and have lower risk of Alzheimer's disease ^[31]. Research suggests that the underlying mechanism involves insulin sensitivity ^{[32, 33]}.

Perhaps most compelling is the link between lower insulin levels and longevity. Studies of centenarians have found that these exceptionally long-lived individuals had fasting insulin below 5 μIU/mL throughout their lives ^[34]. These individuals exhibit unique genetic signatures related to insulin signalling, sensitivity, and metabolism.

Maintaining fasting insulin levels within the 2.6-5 μIU/mL range represents a proactive strategy for long-term health optimization. This approach may significantly reduce chronic disease risk while potentially extending both lifespan and healthspan.

The Key Takeaway

Elevated fasting insulin levels, even within conventionally "normal" ranges, are a significant risk factor for metabolic dysfunction, cardiovascular disease, cognitive decline, and other health issues. Traditional reference ranges are too permissive, allowing for silent progression of insulin resistance and its associated complications.

Superpower's recommended optimal fasting insulin range of 2.6-5 μIU/mL is grounded in scientific evidence. Maintaining insulin levels within this range is associated with enhanced metabolic health, reduced disease risk, and increased longevity. By aiming for this lower range, we can identify and address potential health risks before they develop into serious conditions.