Effects of within-person variability in spot urinary sodium measurements on the associations with blood pressure and risk of cardiovascular disease in 0.5 Million adults in UK Biobank

Background

Randomised control trials have demonstrated direct positive and causal associations of 24-hr measurements of urinary sodium excretion on blood pressure. However, prospective studies, which often used spot (not 24-hr) measurements of urinary sodium, have reported J-shaped associations with higher risks of cardiovascular disease (CVD) at sodium intake <4 g/day. The reasons for the discrepant results are not fully understood, but have prompted some to question the World Health Organisation's recommendations to restrict sodium intake to <2.3g/day.

Purpose

We examined the effects of within-person variability in spot urinary sodium (UNa) measurements on immediate and delayed associations of UNa with blood pressure at baseline and at resurvey, and with incident cardiovascular disease in the UK Biobank (UKB).

Methods

Baseline spot urine samples were measured in 502,619 adults at baseline and in 20,346 participants who were resurveyed at 4 years after baseline. Linear regression was used to assess associations of baseline UNa measurements with systolic blood pressure (SBP; mmHg) at baseline and at resurvey. Cox regression was used estimate the associations between baseline measures of UNa with incident CVD events (recorded from linkage with hospital records). All analyses were adjusted for confounders and corrected for regression dilution bias.

Results

After excluding participants with prevalent diseases, the primary analyses involved 386,060 adults who were followed-up for a median of 7.8 years, during which ∼13,000 CVD events occurred. Estimated mean (SD) urinary sodium excretion was 77.4 mmol/L (SD 44.4, IQR = 42.8–103.7 mmol/L), and mean SBP/DBP were 137.5/82.3 (SD 18.5/10.1) mmHg, respectively. Within-person variability in UNa was high, with a self-correlation of 0.35 at 4 years between measurements. After adjustment for confounders and correction for regression dilution bias, a 100 mmol/L higher UNa was associated with an immediate 3.2 mmHg higher SBP (95% confidence interval [CI]: 2.8–3.6) in cross-sectional analyses (Figure 1). However, the corresponding associations of baseline UNa with SBP at resurvey was completely attenuated (p=0.20). The predicted risk of CVD was 1.06 (95% CI 1.06–1.07, p<0.001) for a 3.2 mmHg higher SBP, but the observed risk for a 100 mmol/L higher UNa was 0.95 (95% CI 0.82–1.10, p=0.47) (Figure 1).

Conclusions

While spot measurements of UNa were strongly associated with immediate effects on SBP, the magnitude of within-person variability in UNa precluded detection of associations with SBP several years after baseline or with risk of CVD. The extreme within-person variability in spot UNa may explain the discrepant results of the trials and observational studies of sodium and blood pressure.

Figure 1. Spot UNa with SBP and CVD in UK Biobank

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): Core funding from the Medical Research Council-Population Health Research Unit, British Heart Foundation

P656Risk of major gastrointestinal bleed in relation to vascular disease risk in 0.5M UK Biobank participants

Background

Low-dose aspirin is of established benefit for secondary prevention of cardiovascular events but in primary prevention the benefit is finely balanced with the hazard of major bleeds, and in particular gastrointestinal (GI) bleeds.

Purpose

To investigate non-vascular, non-genetic risk factors for major GI bleeds and derive a score for GI bleed risk which may help identify who will receive most net benefit from aspirin.

Methods

In the UK Biobank prospective study of 0.5M participants aged 40–69 at recruitment, prior history of cardiovascular disease, bleeds and other medical conditions was ascertained from self-reported diagnoses and electronic heath records (EHR) prior to recruitment. Major GI bleed during 6 years of follow-up was defined based on coded diagnoses and duration of hospital stay. Non-vascular risk factors for bleed were identified from amongst 100 baseline and prior disease factors using a stepwise regression with adjustment for established vascular risk factors, aspirin and warfarin use. 10-way cross-validation was used when making risk scores.

Results

Among the primary prevention population without prior intracranial bleed, serious extracranial bleed or gastrointestinal ulcer in the 6 months prior to recruitment, 1682 (0.06%/y) participants had a major GI bleed (1006 upper GI, 676 lower GI) with a mean stay in hospital of 3.2 days. Antiplatelet use (in 11%) and anticoagulant use (in 1%), were associated with 1.5 and 4 fold risks of GI bleed, respectively. Stepwise regression identified a non-vascular risk score for major bleed with a 4-fold risk ratio across fifths (Figure). But the score was also associated with a 2-fold risk ratio for major vascular events.

Conclusions

Major GI bleeds cause substantial morbidity. A 4-fold difference in bleed risk across quintiles was distinguishable by a score based largely on EHR prior disease information and frailty measures. This score is applicable in other contexts and will be applied in the ASCEND randomised trial of daily aspirin to provide randomized evidence of the net benefit of aspirin in different risk categories. However, vascular risk factors predicted risk of GI bleeds, and non-vascular risk factors for GI bleed predicted risk of major vascular events; so the net benefit from aspirin may vary only modestly across categories by vascular and bleed risks.

Optimization and biochemical characterization of a bacteriocin from a newly isolated Bacillus subtilis strain 14B for biocontrol of Agrobacterium spp. strains

AIMS

The identification of a new compound active against Agrobacterium tumefaciens.

METHODS AND RESULTS

The culture conditions of a newly isolated Bacillus subtilis strain, designed 14B, were optimized, as a first step, to produce its bacteriocin (termed Bac 14B) for the biocontrol of Agrobacterium spp., the causal agents of the crown gall disease. Bac 14B was then partially purified and biochemically characterized. Bacillus subtilis 14B was observed to produce an antibacterial compound having a protinaceous nature. As estimated by sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE), the semi-purified bacteriocin substance was found to be a monomeric protein with a molecular weight of 21 kDa. While the latter's antimicrobial activity was completely stable during exposure to a temperature range of up to 100 degrees C for 2 h, its initial activity was totally lost at 121 degrees C for 20 min. The maximum bacteriocin production (4096 AU ml(-1)) was recorded after 96 h-incubation in an optimized Luria Bertani medium supplemented with 10 g l(-1) glucose, 15 g l(-1) K(2)HPO(4) and 5 g l(-1) MgSO(4) 7H(2)O at 30 degrees C in a shaking flask culture. Interestingly, the B. subtilis 14B culture supernatant that contained the bacteriocin under study was proved efficient in reducing both the percentage of galled plants and the number of galls in tomato.

CONCLUSION

The findings revealed that B. subtilis 14B and its bacteriocin are efficient in reducing the percentage of infections in plants caused by Ag. tumefaciens.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results could be useful for the nurserymen who are particularly interested in the biocontrol of the crown gall disease.