Body mass index modifies cardiovascular risk across blood pressure categories, particularly among underweight adults with hypertension: a 6.3 million‑person nationwide Japanese cohort study

Co-occurring obesity and hypertension is associated with high cardiovascular risk, whereas the prognostic significance of underweight in the presence of hypertension remains uncertain. We examined whether the association between body mass index category and 10-year risk of major adverse cardiovascular events differed across blood pressure categories. Using the Japan Medical Claims Database from 2005 to 2023, we analyzed 6,262,298 adults without prior cardiovascular disease, chronic renal failure, dialysis, or antihypertensive medication use at baseline. Blood pressure was classified as normal (