Objective:

To quantify the adjusted association of the Spring Festival on HbA1c in a large hospital population using a novel 'lag time-window' approach that accounts for the inherent lag of HbA1c.

Approach:

• Study Design: A single-center retrospective observational study analyzing 300,046 HbA1c tests from a tertiary hospital in China between 2013 and 2025.
• Lag Time-Window Methodology: Defined a 60-day lag window for exposure to the Spring Festival, with nonparametric tests and quantile regression used to adjust for confounding variables including age, gender, season, and department subgroup.

Key Findings:

• The median HbA1c during the lagged Spring Festival week was significantly higher than in the control period (6.1% vs. 6.0%; median difference +0.1%, P<0.001).
• The increase in HbA1c was most pronounced with the 60-day lag, attenuated at 30 days, and absent at 90 days.
• Subgroup analysis indicated the increase was concentrated in patients under diabetes core management (Festival week: 6.2% vs. control: 6.1%, P<0.05).
• Quantile regression confirmed an independent association (β=0.041, 95% CI: 0.021–0.061, P<0.001).

Interpretation:

The Spring Festival is associated with a small but statistically significant worsening of long-term glycemic control, particularly in high-risk patients with established dysglycemia.

Limitations:

• The study's retrospective design may limit the ability to establish causation.
• The control period included other national holidays, which may result in a conservative estimate of the Spring Festival effect.

Conclusion:

The findings indicate that the pre-festival period is a critical window for understanding the impact of the Spring Festival on glycemic control.