Cook N R, Kumanyika S K, Cutler J A
Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02215-1204, USA.
Am J Epidemiol. 1998 Sep 1;148(5):431-44. doi: 10.1093/oxfordjournals.aje.a009668.
Intraperson variability in both blood pressure (BP) and sodium excretion dilutes associations and leads to underestimates of the dose-response relation. The authors applied statistical correction techniques to data from the Trials of Hypertension Prevention (TOHP), Phase I, carried out 1987-1990. Men and women with high normal diastolic BP (80-89 mmHg) were randomized to sodium reduction (n = 327) or a usual care comparison group (n = 417). Regression estimates of the effects of change in sodium and sodium/potassium ratio (Na/K ratio) on blood pressure change in the pooled sample were corrected for both the within-person variance of the excretion measures and the within-person covariance with blood pressure using a multivariate error correction. The estimated cross-sectional reliability was 0.36 for square root(Na) and 0.42 for square root(Na/K ratio) and that for change was 0.31 and 0.28, respectively. Corrected coefficients suggested a decrease of 4.4 mmHg in systolic BP (95% confidence interval (CI) 0.1-8.8) and 2.8 mmHg in diastolic BP (95% CI -0.2 to 5.8) per 100 mmol/24 hour reduction in sodium, and of 3.4 mmHg in systolic BP (95% CI 0.8-6.1) and 1.7 mmHg in diastolic BP (95% CI 0.0-3.5) per unit decrease in Na/K. These results are comparable with those from the Intersalt Study, and suggest that the true effect of sodium change on blood pressure change in normotensives over 18 months is underestimated by more than half in uncorrected data.
血压（BP）和钠排泄的个体内变异性会削弱两者之间的关联，并导致对剂量反应关系的低估。作者将统计校正技术应用于1987 - 1990年进行的高血压预防试验（TOHP）一期的数据。舒张血压处于高正常范围（80 - 89 mmHg）的男性和女性被随机分为减钠组（n = 327）或常规护理对照组（n = 417）。使用多变量误差校正，对合并样本中钠和钠/钾比（Na/K比）变化对血压变化的影响进行回归估计，以校正排泄测量的个体内方差以及与血压的个体内协方差。平方根（Na）的估计横断面可靠性为0.36，平方根（Na/K比）为0.42，变化的可靠性分别为0.31和0.28。校正后的系数表明，每24小时钠减少100 mmol，收缩压降低4.4 mmHg（95%置信区间（CI）0.1 - 8.8），舒张压降低2.8 mmHg（95% CI -0.2至5.8）；每单位Na/K比降低，收缩压降低3.4 mmHg（95% CI 0.8 - 6.1），舒张压降低1.7 mmHg（95% CI 0.0 - 3.5）。这些结果与国际盐摄入与血压关系研究（Intersalt Study）的结果相当，表明在未校正的数据中，钠变化对血压正常者18个月内血压变化的真实影响被低估了一半以上。
