August 16, 2026
People the same age become less alike in health as they get older
A new study finds that people the same age become increasingly different in their burden of chronic illness as they get older
ByRodielon Putol
Editor
Medical guidelines set the age for a colonoscopy, a mammogram, or a blood pressure check largely the same way for everyone
But two people of the same age can carry completely different combinations of health problems. A new study finds that this gap keeps widening
The older people get, the less their chronic conditions resemble each other
The United States Preventive Services Task Force tells adults to start colon cancer screening at 45 and stop at 75
Mammograms are recommended for women between 40 and 74. Those cutoffs use age as a broad marker of when the benefits of screening are likely to outweigh the risks
Joel Cohen and Jonathan Tobin, researchers at Rockefeller University, led the study. Cohen studies mathematical patterns that show up in populations of bacteria, trees, and people alike. Tobin directs community-engaged research at Rockefeller’s Center for Clinical and Translational Science
A single score tracks chronic illness
Cohen and Tobin needed a way to measure how sick each person was, beyond simply counting diagnoses. So they turned to a scoring system called the Charlson Comorbidity Index
It adds points for chronic conditions, with higher weights given to illnesses associated with a greater risk of death. A heart attack or peripheral vascular disease adds one point
A spreading cancer, HIV, or an organ transplant adds six points, the highest weight in the system. Most conditions land somewhere in between
For this study, a Weill Cornell physician built an expanded, 39-condition version of the index and calculated a score for every patient
Sick patients are often left out of research
Tobin leads Clinical Directors Network, a research group built around clinicians at Federally Qualified Health Centers. These centers give low-cost primary, dental, and mental health care to more than 34 million people in low-income communities
For nearly ten years, Tobin has studied a group most research skips: patients with many chronic conditions at once
“Despite being among the sickest patients, people with multimorbidity are also among the least researched,” Tobin said
“They’re often excluded from the studies that eventually inform clinical guidelines and clinical practice because they introduce too many confounding variables.”
So instead of leaving these patients out, Tobin’s team built a trial around them. They screened de-identified records from 238,156 people treated at 16 clinics in Chicago and New York City
Health coaches then worked with almost 2,000 of those patients to see whether early support could keep them out of the emergency room
Health gets more different as people age
Cohen took the larger set of records and compared each person’s age with their comorbidity score. Older patients scored higher on average, and that part surprised no one. What stood out was the spread around that average
“The data show that in general, variability goes up with the average in a mathematically consistent way,” Cohen said
“Specifically, the variance increases when the mean increases. That means that people’s multimorbidity grows increasingly different from the multimorbidity of other people of the same age as they grow older.”
Cohen has documented this kind of pattern before, in things as different as wildlife counts and infectious disease outbreaks
Applied to people, it means two older adults are likely to differ much more in their burden of chronic illness than two younger adults
“In this case, for example, we found that two 70-year-old patients typically have far greater differences in their chronic conditions than two 40-year-old patients—and the variation between people will continue to grow the older the patients are,” Cohen said
“That may be the reason a treatment recommended for someone based on age works for one 70-year-old but is inappropriate for another. A better course of action would be to base treatment on their multimorbidity.”
One clinic system broke the pattern
Patients in three of the four clinic systems, two in New York and two in Chicago, followed this pattern. In the fourth, patients over about 65 had lower average scores and less spread than younger patients there, the opposite of the overall trend
The researchers can’t fully explain the dip from this data alone. One possibility: the sickest patients in that system may be dying or moving into long-term care before old age, leaving a healthier group of survivors behind in the records
Researchers already expected people to build up more conditions as they age. What Cohen tested for the first time was the shape of that variation
“We know intuitively that as you get older, you have more chronic conditions because you have more time to accumulate them, and it’s been well documented that age and multimorbidity are associated,” Tobin said
“However, what wasn’t examined was a mathematical model that describes well the variation in multimorbidity, and that’s what Joel’s analyses found.”
Every patient in the study was measured only once. That leaves three tangled things the records can’t separate: getting older, the era someone was born into, and who survives long enough to be counted
Longer-running records, tracking the same people over decades, would be needed to pull those threads apart
“This new model reinforces the idea that we must embrace the complexity of each individual patient, especially when they have multiple chronic conditions,” Cohen said
“It also may help us to anticipate when someone’s risk of hospitalization increases and make a specific intervention before that occurs. When it comes to medical care and public health, there’s no way that one size can fit all.”
The full study was published in the Journal of Population Ageing
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