BACKGROUND: Claim counts for metabolic syndrome-related diseases have risen steadily, but crude rates conflate healthcare utilization with population age structure. We examined whether these increases persisted after age standardization. METHODS: Annual claim counts (2010-2025) for lipoprotein metabolism disorders (E78), diabetes (E10-E14), hypertension (I10-I15), cardiovascular (I20-I25, I42-I43, I50-I52) and cerebrovascular disease (I60-I69) were drawn from the HIRA Open Database. Crude and age-standardized rates per 100,000 population (2005 standard) were analyzed using Joinpoint regression. RESULTS: Crude rates increased significantly in all five groups. After age standardization, the increase persisted only for lipoprotein metabolism disorders (crude AAPC, 9.36%; standardized AAPC, 7.28%) and was attenuated for diabetes (3.38% vs. 0.61%). Three groups reversed to declining standardized trends: hypertension (1.01% vs. -1.83%), cardiovascular disease (APC, -1.47% from 2012 to 2025), and cerebrovascular disease (APC, -2.82% from 2012 to 2020). CONCLUSIONS: Crude trends did not persist uniformly after standardization, indicating heterogeneity across disease groups. Hypertension reversed from crude increase to standardized decline, whereas lipoprotein metabolism disorders alone retained their increase. These findings suggest that similar crude increases may reflect different underlying dynamics and support further analysis of claims per treated person at prescription level.