DXA-derived body composition and blood pressure in underweight and overweight adolescent girls in rural and urban South Africa

Background: Elevated blood pressure (BP) during adolescence is an early marker of cardiovascular risk, particularly in settings experiencing under and overnutrition. However, the relationship between detailed body composition and BP across nutritional extremes remains poorly understood. We examined associations between dual-energy X-ray absorptiometry (DXA)-derived body composition and BP among underweight and overweight South African adolescent girls to assess multilevel correlates of BP. Methods: The Ntshembo trial included 1268 girls 13-19-years from rural Agincourt and urban Soweto. Participants were selected as underweight or overweight. BP was measured in triplicate at a single visit and classified into clinic BP category ranges. DXA provided measures of fat mass (FM), fat-free soft tissue mass (FFSTM), and related indices. Results: Mean SBP and DBP were 110.0±11.2mmHg and 68.7±8.2mmHg, respectively; 21.1% of participants had elevated or hypertensive-range BP. Overweight adolescents had higher SBP and BP categories compared with underweight adolescents. DXA-derived adiposity measures were positively associated with SBP and BP category. FFSTM showed strong association with SBP. Higher FM/FFSTM was associated with elevated (RRR=4.25, 95%CI:1.77-10.20) and hypertensive-range BP (RRR=19.04, 95%CI:6.43?56.40). Caregiver hypertensive-range BP was independently associated with adolescent hypertensive-range BP (RRR=1.72-1.82). Sedentary behaviour independently associated with elevated BP, highlighting a modifiable behavioural target alongside intergenerational risk. Associations were more consistent for SBP than DBP. Conclusions: both FM and FFSTM positively associated with BP, particularly SBP. Regional percentage analyses were consistent with higher BP when a greater proportion of total fat was distributed centrally rather than peripherally.