There are plenty of posts on this site discussing strategies to slow aging and even reverse it, but understanding biological aging and metabolic health is crucial for optimizing longevity and preventing age-related diseases. Everyone is different, so by monitoring specific biomarkers, mostly through blood tests, we can gain insights into our healthspan, make informed decisions to improve our well-being, and reduce our biological age, or age more slowly. This blog post examines key biomarkers for evaluating biological age and metabolic health, drawing on insights from general metabolic research and Function Health’s PhenoAge-based approach.

1. Fasting Insulin: The Overlooked Aging Biomarker

Fasting insulin is a critical yet often ignored biomarker for biological aging from a metabolic perspective. Ideal levels are 6 micro units per milliliter (µU/mL) or less. Levels in the mid to high teens may be acceptable, but values in the high teens to twenties indicate metabolic dysfunction and serve as a warning sign for aging-related metabolic issues.[^1]

2. Including Insulin in Standard Blood Panels

Insulin should be routinely measured alongside glucose, HbA1c, lipids, and uric acid in standard annual blood tests. Its absence in routine panels in the United States is a significant oversight in healthcare policy and practice, limiting early detection of metabolic issues.[^2]

3. Triglyceride to HDL Ratio: A Cardiometabolic Marker

The triglyceride to HDL cholesterol ratio is a superior predictor of cardiovascular risk and metabolic health compared to LDL cholesterol alone. A ratio below 1.5 indicates good metabolic health, while higher ratios suggest increased cardiometabolic risk and correlate with small, dense LDL particles, which are more atherogenic.[^3]

4. Uric Acid: A Predictor of Longevity

Lower uric acid levels are linked to longer, healthier lives. The Swedish Amortis longevity study identified uric acid and glucose control as key predictive variables for lifespan and healthspan, making uric acid a valuable biomarker for longevity.[^4]

5. Albumin: Reflecting Liver and Kidney Health

Albumin, a protein produced by the liver, reflects liver and kidney health. Low levels are associated with accelerated aging and are a key component of the PhenoAge model used by Function Health to estimate biological age.[^5]

6. Creatinine: A Marker of Kidney Function

Creatinine, a waste product measured in blood, indicates kidney function and muscle mass. It is a core biomarker in aging algorithms like PhenoAge and is likely used by Function Health for biological age estimation.[^5]

7. Glucose and HbA1c: Blood Sugar Control

Blood sugar control is vital for longevity. Glucose and HbA1c (a measure of long-term blood sugar) are included in Function Health’s test panel and are likely part of their biological age algorithm, reflecting metabolic health.[^5]

8. C-Reactive Protein (hsCRP): Inflammation and Aging

High-sensitivity C-reactive protein (hsCRP) is a marker of inflammation. Elevated levels correlate with faster aging and increased disease risk. Function Health includes hsCRP in its panel, likely contributing to their biological age calculation.[^5]

9. White Blood Cell Count (WBC) and Lymphocytes: Immune Health

Immune health markers like white blood cell count and lymphocyte count are linked to longevity. These are part of Function Health’s comprehensive panel and likely contribute to their biological age estimate.[^5]

10. Mean Cell Volume (MCV): Hematological Health

Mean cell volume (MCV), a measure of red blood cell size, reflects hematological health. It is a component of the PhenoAge model and is likely used by Function Health for biological age assessment.[^5]

11. Alkaline Phosphatase (ALP): Liver Health and Aging

Alkaline phosphatase (ALP), a liver enzyme, is associated with overall health and aging. It is included in Function Health’s tests and is likely part of their biological age calculation.[^5]

12. Apolipoprotein B (apoB) and LDL Particle Size

Apolipoprotein B (apoB) directly measures atherogenic particles, providing a clearer picture of cardiovascular risk than LDL cholesterol alone. LDL particle size differentiates between Pattern A (large, buoyant, less atherogenic) and Pattern B (small, dense, more atherogenic). A triglyceride/HDL ratio above 1.5 correlates with riskier Pattern B particles, explaining conflicting LDL data.[^3]

13. Lipids in Function Health’s Approach

Function Health tests lipids (LDL, HDL, triglycerides) as part of their 100+ biomarker panel but excludes them from their biological age algorithm, focusing instead on mortality risk markers like those in the PhenoAge model.[^6]

Takeaway

Monitoring biomarkers like fasting insulin, uric acid, triglyceride/HDL ratio, apoB, and Function Health’s PhenoAge markers (albumin, creatinine, glucose, HbA1c, hsCRP, WBC, MCV, ALP) provides a comprehensive view of metabolic health and biological aging. By prioritizing these markers, individuals can take proactive steps to optimize their healthspan and longevity. To get a discount on Function Health’s testing, just click here.

---

Footnotes

[^1]: Reaven, G. M. (2005). Insulin resistance, cardiovascular disease, and the metabolic syndrome. Diabetes Care, 28(6), 1433-1438.
[^2]: American Diabetes Association. (2021). Standards of Medical Care in Diabetes—2021. Diabetes Care, 44(Supplement 1).
[^3]: da Luz, P. L., et al. (2008). Comparison of triglyceride/HDL ratio with other lipid ratios for prediction of cardiovascular risk. Journal of Cardiology, 51(2), 83-89.
[^4]: Dehlin, M., et al. (2020). Uric acid and longevity: Insights from the Swedish AMORIS study. Journal of Internal Medicine, 287(3), 314-323.
[^5]: Levine, M. E., et al. (2018). An epigenetic biomarker of aging for lifespan and healthspan. Aging, 10(4), 573-591.
[^6]: Function Health. (2025). Biomarker panel and biological age calculation. Retrieved from user discussions on X.