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Low back pain, disability, and biological aging: routinely measurable clinical clocks versus epigenetic clocks (NHANES)

In a nationally representative analysis of the NHANES population, neither routinely measurable clinical aging clocks nor epigenetic clocks were found to be associated with low back pain or disability, indicating that the aging-clock signals observed in smaller, selected cohorts do not generalize to the broader population and that biological age acceleration is not a useful bedside risk marker for these conditions.

Original authors: Adil Can Karaoğlu

Published 2026-10-05

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CC BY 4.0

Original authors: Adil Can Karaoğlu

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

For decades, doctors have known that getting older does not mean everyone ages at the same speed. A person who is sixty years old might feel and function like a healthy fifty-year-old, while another might struggle with the frailty of someone much older. This gap between the number of years on a birth certificate and the actual condition of the body is called biological aging. In recent years, scientists have developed tools to measure this invisible process. Some tools, known as clinical clocks, use routine blood tests that doctors already order to estimate how fast a person's body is wearing down. Others, called epigenetic clocks, look at chemical tags on DNA to measure aging with high precision, but these require specialized lab work that cannot be done in a standard doctor's office.

The question driving this research is whether these biological clocks can predict a very common and debilitating problem: low back pain. Low back pain is the leading cause of disability worldwide, and it often strikes people who are not yet elderly. Previous studies in small groups of patients suggested that people with faster biological aging were more likely to suffer from chronic pain. This raised a hopeful possibility: that a simple blood test could one day warn doctors which patients are at risk, allowing for earlier intervention. However, those earlier studies looked at specific groups of people who were already in pain or had spinal deformities. It remained unknown whether these biological signals would hold up when looking at the general population, where people have a wide mix of health and pain levels.

A researcher decided to test this idea on a massive scale using data from the National Health and Nutrition Examination Survey, a major study that represents the entire adult population of the United States. They focused on adults over fifty, a group where back pain and aging are most relevant. The researcher gathered data on thousands of individuals, calculating their biological age using both the routine blood tests and the specialized DNA analysis. They then asked these participants if they had experienced low back pain in the last three months and whether they had any physical limitations that made daily tasks difficult. The goal was to see if the people with the fastest biological aging were the ones reporting the most pain and disability, and to see if the simple blood tests matched the complex DNA results.

The results were clear and unexpected. After analyzing the data with careful statistical methods to ensure accuracy, the researcher found no link between biological aging and low back pain. Whether they looked at the routine blood-based clocks or the advanced DNA-based clocks, none of them could predict who had back pain or who was disabled. The people with the fastest biological aging were no more likely to have pain than those with slower aging. Furthermore, the two types of clocks gave the same result: neither the simple blood test nor the complex DNA test offered any advantage in identifying back pain risk. The study also found that these biological clocks did not predict physical disability in this general population, even though they are known to predict other health outcomes like mortality.

This finding suggests that the signals seen in small, selected groups of patients do not apply to the wider world. The researcher explains that while biological aging is real and measurable, it may not be the primary driver of back pain for most people. It is possible that back pain is caused by local issues in the spine or muscles that do not show up in a general blood test or a DNA sample from white blood cells. The study concludes that for the specific problem of low back pain, biological age acceleration is not a useful tool for doctors to use at the bedside. Neither the routine clinical clocks nor the advanced epigenetic clocks add value to the current understanding of who is at risk, and the hope of using these tools as a simple screening test for back pain is not supported by this large-scale evidence.

Technical Summary: Low Back Pain, Disability, and Biological Aging (NHANES)

Problem Statement
Low back pain (LBP) is the leading global cause of disability, yet chronological age is a poor predictor of which older adults develop disabling pain. While biological aging clocks (epigenetic and clinical) have shown promise in small, selected cohorts—distinguishing chronic pain patients from controls or predicting surgical outcomes—it remains untested whether these signals generalize to an unselected national population. A critical clinical question remains: can a "clinical clock" derived from routine blood chemistry (deployable at the bedside) capture the same risk signal as "epigenetic clocks" (requiring DNA methylation, unavailable at the bedside) for LBP and physical-function disability?

Methodology
This study presents a cross-sectional analysis of the National Health and Nutrition Examination Survey (NHANES) cycles 1999–2002, reported following STROBE guidelines.

Population: The analysis utilized a "context layer" of 10,291 adults (≥20 years) and a "core layer" DNA-methylation subsample of 2,532 adults (≥50 years) with complete clock and covariate data.
Exposures (Aging Clocks):
- Clinical Clocks: Phenotypic Age (PhenoAge) and Klemera–Doubal Biological Age (KDM), calculated from routine blood chemistry and hematology.
- Epigenetic Clocks: First-generation (Horvath, Hannum, Skin-and-Blood), second-generation (DNAm-PhenoAge, GrimAge2), and pace-of-aging (DunedinPoAm) measures derived from DNA methylation.
- All clocks were expressed as age acceleration (residuals from regressing clock on chronological age) and standardized per standard deviation (SD).
Outcomes: Primary outcomes were self-reported low back pain in the past three months and physical-function disability (self-reported limitation).
Statistical Approach: Survey-weighted regression (logistic for LBP, linear for disability) adjusted for chronological age, sex, race/ethnicity, education, BMI, smoking, alcohol, physical activity, and comorbidity (Charlson index).
Hypothesis Testing: The primary contrast was the "same-name pair": clinical PhenoAge versus its methylation counterpart (DNAm-PhenoAge). Multiplicity was controlled hierarchically using false discovery rate (FDR) methods. The study was prospectively preregistered.

Key Results

No Association with Low Back Pain: In the DNA-methylation subsample, no aging clock (clinical or epigenetic) was associated with low back pain in the past three months. Adjusted odds ratios (OR) per SD ranged from 0.64 (clinical PhenoAge) to 0.99 (KDM acceleration), with all 95% confidence intervals crossing the null (OR=1).
No Difference Between Clock Types: The primary contrast between clinical PhenoAge and DNAm-PhenoAge showed no significant difference (Ratio of ORs = 0.80, 95% CI: 0.15–4.25; p=0.79).
No Association with Disability: After FDR control, no clock was associated with physical-function disability. Standardized $\beta$ coefficients were negligible (range −0.016 to 0.075).
Specific Findings: The only association reaching nominal significance was between clinical PhenoAge and the deficit-accumulation frailty index ( $p=0.012$ ), an expected correlation given their shared physiological inputs, but this did not translate to independent predictive value for pain or disability.
Robustness: A comprehensive post hoc exploratory sweep (210 tests) yielded no associations surviving false-discovery correction.

Key Contributions

Generalizability Test: This is the first study to test whether biological-age acceleration signals for LBP, previously observed in small, selected cohorts (e.g., chronic pain vs. controls, surgical deformity), hold true in a nationally representative, unselected population. The study demonstrates that these signals do not generalize.
Clinical vs. Epigenetic Comparison: It provides the first head-to-head comparison of routinely measurable clinical clocks versus epigenetic clocks for back pain outcomes, finding that clinical clocks add no value over epigenetic clocks (as both were null) and that epigenetic clocks offer no advantage over clinical clocks for this specific outcome.
Outcome Specificity: The study clarifies that while these clocks are valid predictors for other outcomes (e.g., all-cause mortality, cognitive performance) in the same NHANES subsample, their utility is outcome-specific and does not extend to LBP or physical-function disability at the population level.

Significance and Claims
The paper concludes that biological-age acceleration is not a usable bedside risk marker for low back pain. The findings suggest that the "aging-clock" signals reported in small, selected cohorts are likely artifacts of extreme group separation rather than generalizable population risk factors. Consequently, ordering clinical or epigenetic aging clocks to stratify low back pain risk is not supported by this data. The study emphasizes that while frailty (a clinical deficit accumulation) remains a practical axis for risk stratification in spine practice, molecular and physiological aging clocks do not currently offer additional predictive value for the onset or disability associated with low back pain in the general population.

Technical Summary: Low Back Pain, Disability, and Biological Aging (NHANES)

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