Exploring the Linear and Non-linear Association Between BMI and Night-Time Blood Pressure Variability

The relation between obesity and blood pressure (BP) is well known; however, its relationship with night-time BP and BP variability (BPV) has not been adequately examined.

To examine the relationship between obesity and night-time BP/BPV.

Data from 6,767 adults (46.4% males), aged 56.0 ± 14.0, were collected during their visit to the Outpatient Hypertension Unit of a single institution and had valid ambulatory BP monitoring and anthropometric data. Body mass index (BMI) was estimated by weight and height measurements that took place at the office and categorized as normal weight [< 25 kg/m²; 1,719 (25.4%)], overweight [25-29.9 kg/m²; 2,976 (43.0%)] or obesity [≥ 30 kg/m²; 2,072 (30.6%)]. Standard deviation (SD) and coefficient of variation (CV) of BP were used as indices of BPV.

After adjusting for confounders, BMI was significantly related to night-time systolic (b = 0.38, 95%CI: 0.31-0.46) and diastolic BP (b = 0.10 95%CI: 0.05-0.015). Similarly, after adjusting for confounders, obesity was related to SD (b = 0.25, 95%CI: 0.02-0.49) and CV (b = 0.23, 95%CI: 0.03-0.42) of night-time systolic BPV, while a similar pattern was found for diastolic BPV (p < 0.001). Restricted cubic spline models showed a significant joint effect of splines after adjusting for confounders, for all BPV indices (p < 0.05), but a trend for non-linearity found only for systolic BPV indices (χ² = 3.74, p = 0.053 for SD and χ² = 3.54, p = 0.060 for CV).

In conclusion, the relationship between obesity and both nighttime BP and BPV provides new insights into the possible effects of obesity on the cardiovascular system.