Blood pressure and cardiovascular risk in relation to birth weight and urinary sodium: an individual-participant meta-analysis of European family-based population studies

Background: Although the relation of salt intake with blood pressure (BP) is linear, it is U- shaped for mortality and cardiovascular disease (CVD). This individualparticipant meta-analysis explored whether the relation of hypertension, death or CVD with 24-h urinary sodium excretion (UVNA) or sodium-to-potassium (UNAK) ratio was modified by birth weight. Methods: Families were randomly enrolled in the Flemish Study on Genes, Environment and Health Outcomes (19852004) and the European Project on Genes in Hypertension (1999- 2001). Categories of birth weight, UVNA and UNAK (<= 2500, >2500-4000, >4000 g; <2.3, 2.3-4.6 and >4.6 g; and <1, 1- 2, >2, respectively) were coded using deviation-from-mean coding and analyzed by Kaplan- Meier survival functions and linear and Cox regression. Results: The study population was subdivided into the Outcome (n = 1945), Hypertension (n = 1460) and Blood Pressure cohorts (n 1/4 1039) to analyze the incidence of mortality and cardiovascular endpoints, hypertension and BP changes as function of UVNA changes. The prevalence of low/medium/high birth weight in the Outcome cohort was 5.8/84.5/9.7%. Over 16.7 years (median), rates were 4.9, 8 and 27.1% for mortality, CVD and hypertension, respectively, but were not associated with birth weight. Multivariable-adjusted hazard ratios were not significant for any endpoint in any of the birth weight, UVNA and UNAK strata. Adult body weight tracked with birth weight (P< 0.0001). The partial r in the low-birth-weight group associating changes from baseline to follow-up in UVNA and SBP was 0.68 (P = 0.023) but not significant in other birth weight groups. Conclusion: This study did not substantiate its prior hypothesis but showed tracking of adult with birth weight and suggest that low birth weight increases salt sensitivity.