Association Between Baseline C-reactive Protein–Triglyceride–Glucose Index and Incident Asthma: A Prospective Cohort Study from the CHARLS

Asthma is often thought of as a condition that lives entirely in the lungs, a matter of inflamed airways and sudden breathing difficulties. For decades, doctors have understood that the immune system plays a central role, often reacting to allergens or irritants. However, a growing body of research suggests that the story is more complex. The body's metabolic system, which manages how we process sugar and fat, and our systemic inflammation, a low-level fire that can burn throughout the body, are increasingly seen as key players in this respiratory drama. When these systems go out of balance, they can create a specific type of asthma that is harder to treat and often linked to obesity. Scientists have long known that high blood sugar and high inflammation are bad for health, but they have struggled to find a single, simple way to measure how these two forces work together to trigger breathing problems.

To solve this puzzle, researchers turned to a massive database of health records from middle-aged and older adults in China. They were looking for a connection between a new, combined health score and the future development of asthma. This score, known as the C-reactive protein–triglyceride–glucose index, acts like a single snapshot that captures both the body's struggle with insulin and its level of chronic inflammation. By tracking over 12,000 people for seven years, the team wanted to see if a high score at the start of the study predicted who would later be diagnosed with asthma. The study, which followed participants from the China Health and Retirement Longitudinal Study, offers a clear view of how metabolic health and breathing are linked over time.

The researchers began by gathering blood samples and health data from 12,359 participants who did not have asthma at the start of the study. They calculated the combined score for each person using three specific measurements taken from their blood: the level of C-reactive protein, a marker for inflammation; triglycerides, a type of fat in the blood; and fasting glucose, the amount of sugar in the blood after not eating for a while. These three numbers were blended into a single value that reflects the body's overall metabolic and inflammatory stress. The team then waited, following these individuals through regular health surveys over a median period of seven years to see who would develop asthma.

During this seven-year period, 456 participants, representing about 3.7 percent of the group, received a new diagnosis of asthma from a doctor. The analysis revealed a steady, linear relationship between the initial health score and the risk of developing the disease. For every single unit increase in the score, the risk of developing asthma rose by 17 percent. This was not a sudden jump that happened only at very high levels; rather, the risk climbed steadily as the score increased. When the researchers looked at the group with the highest scores compared to those with the lowest, the high-scoring group faced a 58 percent higher risk of developing asthma. This pattern held true even after the researchers carefully adjusted for other factors that could influence the results, such as age, gender, education, smoking habits, body weight, and existing conditions like high blood pressure or heart disease.

One of the most striking findings was that this connection depended heavily on whether the person already had diabetes. The strong link between the high score and future asthma was found clearly in people who did not have diabetes. In this group, a higher score meant a significantly higher chance of developing asthma. However, among the participants who already had diabetes, the connection disappeared. The researchers suggest that this might be because the metabolic and inflammatory systems in people with established diabetes are already so altered that the score no longer predicts new risks in the same way. It is possible that the medications these individuals take, or the long-term changes their bodies have undergone, mask the early warning signs that the score is designed to catch.

The study also looked at how well this score could predict asthma compared to other factors. The score performed reasonably well as a predictor, with a statistical measure of accuracy that placed it in a moderate range, similar to how a standard blood test might predict heart disease risk. The researchers confirmed that the results were robust by running the data through different statistical models, including those that accounted for the fact that some older participants passed away during the study before they could develop asthma. Even when they removed people who developed asthma very quickly after the study began—ruling out the possibility that undiagnosed asthma was causing the high scores—the link remained strong. This suggests that the metabolic and inflammatory imbalance measured by the score likely happens before the breathing problems start, rather than being a result of them.

While the findings are compelling, the researchers noted several limitations. The diagnosis of asthma relied on participants reporting that a doctor had told them they had the condition, rather than on direct lung function tests performed by the study team. Additionally, the score was only measured once at the beginning of the study, so the researchers could not track how changes in the score over time might affect risk. The study population consisted entirely of middle-aged and older Chinese adults, so it is unclear if these results apply to younger people or those from different ethnic backgrounds. Despite these caveats, the study provides a clear signal that the body's metabolic and inflammatory health is deeply intertwined with respiratory health.

This research highlights a potential new way to identify people at risk for asthma before they ever experience a breathing attack. Because the score is built from common blood tests that are already part of routine medical checkups, it offers a practical and inexpensive tool for doctors. It suggests that managing blood sugar and reducing systemic inflammation might be just as important for preventing asthma as avoiding allergens. By focusing on the whole body's metabolic state, rather than just the lungs, doctors may be able to spot the early signs of trouble and intervene sooner, potentially preventing the disease from taking hold in vulnerable individuals.