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Circulating protein levels may serve as biomarkers of cardiorespiratory fitness, a key component of overall health that has previously been difficult to measure, the researchers said. Nature Medicine.
Cardiopulmonary fitness is an indicator of overall health, but there is currently no standardized way to measure it, said study co-author Ravi Kalhan, M.D., professor of preventive medicine in the divisions of Pulmonary and Critical Care Medicine and Epidemiology.
“As a physician who sees patients, I can’t gauge the health of the patient sitting in front of me,” said Calhan, who is also the Lewis A. Simpson Professor of Pulmonary Medicine. “We can do a variety of sophisticated tests, but it’s a huge undertaking, and not all patients, such as older adults or those with chronic lung disease, can walk on a treadmill.”
Culhan said that because cardiopulmonary function affects nearly every system in the body, from metabolism to the brain, developing ways to measure it could help doctors accurately assess overall health.
“This is a much more comprehensive confirmation that we were trying to measure through biomarkers rather than a single biomarker that reflects an organ system, like LDL cholesterol,” Culhan said.
In the study, Calhan and his colleagues used statistical models to identify circulating proteins that have the greatest impact on overall health in more than 14,000 subjects. The researchers then created a cardiorespiratory fitness score that takes into account individual levels of key circulating proteins involved in inflammation, neuronal survival and growth, oxidative stress, and more.
The researchers then tested the scoring system using data from 20,000 people from UK Biobank and found that better scores were associated with a lower risk of all-cause mortality, according to the study.
To further test the scoring system, the researchers analyzed circulating proteins in more than 600 people before and after a 20-week exercise program. Findings showed that study participants’ cardiorespiratory fitness scores correlated with the positive effects that exercise had on the cardiorespiratory system.
Culhan said the findings could provide the basis for a scoring system that could accurately assess overall health with a simple blood test, helping scientists better understand the relationship between fitness and health.
“We don’t yet fully understand why improving fitness improves health,” Culhan says, “but in the long term, this study may help us understand the biology of what happens when people improve their fitness so we can understand the mechanisms and target specific biological pathways to improve health.”
Culhan said he and his colleagues plan to build on this development and try to apply the protein-scoring approach to other areas of overall health.
“We know a lot about health trajectories. Someone may be on a decline, but it’s very hard to infer what that person’s health trajectory is when you see them at a point in time,” Culhan says. “If we can apply these single-point-in-time measurements using blood tests that reflect larger, harder-to-see health factors, that’s really interesting.”
Northwestern Medicine co-authors on the study include Sadiya Khan, MD ’09, MS ’14, MD ’10, MD ’12, Magerstadt professor of cardiovascular epidemiology, Li-Fan Hou, MD, PhD, chief of Cancer Epidemiology and Prevention in the Division of Preventive Medicine, and Donald Lloyd-Jones, MD, MS, Eileen M. Foell Professor of Cardiac Research.
The study was supported by the American Heart Association with additional funding from the National Institutes of Health.