Aging Makes Us Less Alike, Not More, Study Finds

Getting older almost always means collecting more health problems along the way. That much is well known. But new research reveals something that appears not to have been studied empirically before: not only do older adults carry a greater burden of chronic illness on average, but the variation in that burden among people of the same age grows wider as they age. Two 70-year-olds can look completely different on paper, medically speaking, and that gap widens with age.

In a study published in the Journal of Population Ageing, researchers analyzed de-identified electronic health records from 238,156 adults served by four United States health systems in low-income communities, two in Chicago and two in New York City. Using a well-established scoring tool that counts and weighs the severity of up to 39 chronic conditions at once, they found that as average illness burden rises with age, the variation in illness burden generally rises right along with it. Older age groups are not just sicker on average — they are also far more uneven in their health profiles than younger groups.

That finding carries weight for anyone who has ever assumed that people of a similar age share roughly similar health needs. According to this research, that assumption becomes increasingly unreliable as people get older.

How Researchers Measured Illness Across 238,000 Patients

To gauge how sick each person was, the team used a scoring system called the enhanced Charlson Comorbidity Index. It draws on 39 categories of chronic conditions and weights each by severity, so a serious illness adds more to a person’s score than a milder one does.

What made this study stand out is that rather than simply asking what the average score is for a 65-year-old versus a 75-year-old, the team asked a deeper question: how much do scores spread out within any given age bracket? That spread appears not to have been studied empirically before in the context of aging and multiple chronic conditions.

Across all four health systems, a broadly consistent pattern emerged in eCCI scores. As the average illness score for an age group went up, the variation within that age group generally went up too, and not in a small way. The researchers found that within-age-group illness scores were well approximated by a negative binomial distribution — a statistical model in which variance exceeds the mean, reflecting how illness spreads unevenly across individuals rather than clustering neatly around a typical value.

Researchers also found that the relationship between average illness score and its spread follows a mathematical rule originally used in ecology to explain how variability in a population scales with its size. The fact that this relationship held across all four health systems suggests the pattern is real, not a quirk of one city or one hospital network. The one notable exception came in a single health system, where both the average and the spread declined after roughly age 65 — a reversal the authors suggest could reflect the selective loss of the sickest patients from active records through institutionalization or death, though their data cannot confirm that.

Why This Matters for Doctors and Policymakers

Healthcare systems often organize resources around what a typical patient in a given age range looks like. A hospital might expect that most 72-year-olds will have a certain level of need and plan staffing or services accordingly. But this research shows that within any age group, especially older ones, the range of actual patient complexity is enormous.

The study’s authors conclude that both clinical care and health policy need to account for the variation and heterogeneity of multimorbidity among older adults, rather than treating them as a uniform group or assuming a predictable curve of need. If the spread of illness within age groups is wider than frameworks built on averages assume, those averages may paint a misleading picture of what an aging population actually needs.

Aging Is Not a One-Size-Fits-All Experience

What this study makes plain is that aging is not a uniform experience, at least not medically. While everyone’s risk of accumulating chronic conditions increases with age, how much illness any individual ends up carrying is far from predetermined by age alone. A patient’s age tells part of the story. How much variation sits within that age group tells a much more complicated one, and for the 238,156 people in this dataset, the data made that gap impossible to ignore.

Disclaimer: This article summarizes findings from a single peer-reviewed study and is for general informational purposes only; it is not medical advice. The research is cross-sectional, meaning it captured patients at one point in time and cannot establish cause and effect or explain why illness variation increases with age. The data came from four health systems serving low-income communities in Chicago and New York City and may not represent the broader U.S. population. Anyone with questions about their own health or chronic conditions should consult a qualified healthcare professional.

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