| Objective:It has been widely recognized that excessive sodium consumption could increase blood volume and the resistance of peripheral vessels,resulting in increased blood pressure and cardiovascular disease.Salt as the main sources of dietary sodium,salt reduction become the most cost-effective public health strategy for prevention of hypertension and cardiovascular disease in developed and developing countries.In China,affected by traditional Chinese dietary habits,salt consumption was confirmed to be the highest in the world,with adults consistently consuming on average above10 grams of salt a day（12.9g/d in 1992,12g/d in 2002 and 10.5g/d in 2015）,more than twice the WHO（World Health Organization）recommended limit（5g/d）.Therefore,it is imperative to explore a suitable salt reduction pattern without changing dietary culture and habits of Chinese.Low-sodium salt,one of the several existing salt reduction strategies available on the market,composed of 65%sodium chloride,25%potassium chloride and 10%magnesium sulfate.Compared to normal salt,low-sodium salt could significantly decrease sodium intake under circumstance without changing total salt intake.However,to date,no evidences about the long-term effect of low-sodium salt on cardiovascular events or mortality among general population have been published.Salt sensitivity of blood pressure was found in studies about the relationship between salt and blood pressure.Researchers found that blood pressure levels of individuals showed different responses to salt load or salt restriction.The previous results of our study demonstrated the changing of blood pressure was different according to different individuals,which means the effect of low-sodium salt intervention might be influenced by genetic factors.Therefore,selecting the low-sodium salt susceptible genes to lower blood pressures and prevent cardiovascular disease has been a new study topic.Therefore,based on the previous randomized,double-blind,controlled trial,we conducted this retrospective cohort study with participants who finished the previous trial to explore the long-term effect of low-sodium salt on cardiovascular events or death among population with high-risk of hypertension.In addition,we also evaluate the effect of ENaC gene on cardiovascular outcomes by calculating genetic risk scores（GRS）and then built predictive models of cardiovascular outcomes by integrating traditional risk factors and genetic factors,which might provide evidences of popularization and application of low-sodium salt and provide strategies to prevent cardiovascular events among population with high-risk of hypertension.Methods:1.Our study were conducted at two phase,the 1st phase was intervention period（2006-2009）and the 2nd phase was post-intervention period（2009-2019）.The intervention period was a randomized controlled trial,intervention group was distributed with low-sodium salt as family,and control group distributed with normal salt.The intervention lasted for 3 years,and we home-visited every 3 months to obtain the information cardiovascular outcome and death.Post-intervention period was conducted with retrospective cohort study to examine the low-sodium salt intervention’s long-term effect.To determine the time and cause of cardiovascular outcomes,multiple sources were used,including death certificates,medical records,and symptoms as reported by the relatives（spouse,sibling,or child）and then cross-checked with death registration system or new rural cooperative medical care system.The end-points of investigations including mortality（cardiovascular mortality,all-cause mortality）,cardiovascular morbidity（incidence and occurrence）and composite cardiovascular events（stroke,acute coronary syndrome and vascular death）.Data analysis was conducted with SPSS 23.0 software.Comparisons of baseline characteristics between groups were conducted with t-test,Mann-Whitney U test and?2 tests.Comparisons of cumulative incidence（occurrence,mortality）were conducted with Log-rank test and Cox regression was used to evaluate the association between low-sodium salt and different end-point outcomes.2.Based on the previous followed-up results,we conducted the follow-up studies among the populations who already finished the 3-year intervention and collected blood samples.We evaluate the traditional risk factors（age,gender,smoking,alcohol drinking,history of disease,medication use and indicators of serum lipids）and genetic factor（ENaC gene）together and different cardiovascular outcomes.About the genetic analysis,four different GRS（SC-GRS,DL-GRS,PG-GRS,EV-GRS）were used to build predictive model of cardiovascular outcomes and chose the best GRS for outcomes.Then,models with both traditional risk factors and genetic factors were built to predict cardiovascular outcome and we evaluated the models with discrimination and calibration.SPSS 23.0 and R 3.5.2 software were used to do the analysis.Univariate and multivariate Cox regressions were used to explore the associations between traditional risk and genetic factors and cardiovascular outcomes.And the evaluation of predictive model used C-index,NRI,IDI and Hosmer-Lemeshow fitted test.Results:1.Total 462 participants enrolled at the initial of trials,including 224participants in low-sodium salt group and 238 participants in normal salt group.After3 years intervention,finally 440 participants finished intervention,including 214 in low-sodium salt group and 226 in normal salt group.During the intervention period,6participants died and 428 participants obtained the information of cardiovascular incidence and death.According to the results of baseline characteristics,only alcohol drinking status was different groups.Among all population,the incidence of all-cause mortality,cardiovascular mortality and composite cardiovascular events incidence in low-sodium salt group was lower than normal salt group during each study periods.Among hypertensive population,the cardiovascular mortality was significantly decreased in low-sodium salt group than normal salt group（4.97%vs.10.91%,P=0.046）.Furthermore,low-sodium salt might lower the cardiovascular mortality among all population in full period（HR=0.407,95%CI=0.177-0.937,P=0.035）and significantly lower the cardiovascular mortality in post-intervention period（HR=0.379,95%CI=0.156-0.922,P=0.032）and full period（HR=0.356,95%CI=0.150-0.849,P=0.019）.2.For population with low-sodium intervention,the results of traditional risk factors demonstrated that baseline age might be the independent risk factor for composite cardiovascular outcomes.For normal salt group population,baseline age was the risk factor for incidence and recurrence of cardiovascular disease;baseline SBP might be the independent risk factor for total death and CVD death.About the analysis of genetic factor,significant association was found between ENaC and cardiovascular incidence and composite cardiovascular events.The PG-GRS of ENa C was associated with cardiovascular incidence（HR=3.475,95%CI=1.018-11.865,P=0.047）,SC-GRS（HR=1.243,95%CI=1.047-1.475,P=0.013）、DL-GRS（HR=2.191,95%CI=1.096-4.382,P=0.027）、PG-GRS（HR=2.582,95%CI=1.142-5.839,P=0.023）and EV-GRS（HR=3.840,95%CI=1.180-12.493,P=0.025）were associated with composite cardiovascular events.For normal salt group population,we also found ENa C was significantly associated with cardiovascular recurrence.About the construction of genetic risk predictive model for population with low-sodium salt intervention,we found PG-GRS showed better predictive power on composite cardiovascular events（C-index（95%CI）=0.596（0.510-0.682））.Furthermore,we integrated the traditional risk factors and genetic factors to build the predictive model of composite cardiovascular outcomes.And compared with traditional risk predictive model or genetic risk predictive model,the integrated model showed better discrimination and calibration.Finally,the best predictive model for composite cardiovascular outcomes was H（t）=exp（0.067×age+0.948×PG-GRS）.Conclusions:1.Low-sodium salt might significantly decrease the risk of long-term cardiovascular mortality among total population or hypertensive population.2.Integrated model with traditional risk factors（age）and genetic factors（PG-GRS of ENa C）was the best predictive model for composite cardiovascular events,and the model was H（t）=exp（0.067×age+0.948×PG-GRS）. |
