Background
The burden of disease related to hypertension remains high. The Global Burden of Disease Study identified high systolic blood pressure as the largest contributor to global disability-adjusted life-years (DALYs) among Level 3 risks (accounting for 211.8 million global DALYs) in 2015 [
1]. Notably, the bulk of hypertension cases are found among older adults, largely because of this group’s dramatically greater prevalence of the condition compared with that of younger people [
2]. Hypertension is also more prevalent in low- and middle-income countries, where those are diagnosed with hypertension may not have the resources or the access to quality care necessary to successfully control their illness over the long term [
3]. Nearly three-quarters of people who have been diagnosed with hypertension reside in low- and middle-income countries [
4]. In China, population aging also represents a significant challenge for hypertension control.
Hypertension seriously affects quality of life for older adults [
5]. However, hypertension can be prevented and controlled effectively by modifying lifestyle and dietary factors known to be associated with the condition [
6,
7]—especially excessive sodium intake and heavy alcohol consumption. The global sodium intake survey found that the average sodium intake was 3–5 g/day in most countries [
8]. However, in China, the problem of excessive sodium intake is serious. The fifth dietary survey conducted in China reported the mean sodium intake to be 14 g/day, which is double the World Health Organization’s recommended intake [
9].
Additionally, heavy alcohol consumption has become increasingly recognised as a leading risk factor for the development of hypertension [
10]. Worldwide, 32.5% of people were current drinkers in 2016, and the burden of disease caused by drinking increases with age, peaking in men aged 55–65 years [
11]. A meta-analysis has shown that decreasing alcohol consumption, which is known to be an effective intervention, reduces the burden of disease caused by hypertension [
12].
The prevalence of hypertension is higher in Inner Mongolia than in other parts of China because of this region’s relatively low rates of awareness, treatment and control, which lead to the earlier occurrence of hypertension in the life course [
13]. Inner Mongolia’s less-developed economy and medical care system and the region’s residents’ lack of awareness regarding health care have resulted in poor public health conditions related to hypertension [
14]. Therefore, hypertension has become a common chronic disease in people over 55 years old in Inner Mongolia, where the crude hypertension prevalence rate has been reported to be 54.10% [
15].
High sodium intake and excessive drinking are prevalent in Inner Mongolia [
16]. Both factors play an important role in the development of hypertension. Most evidence supports a positive association between sodium intake and blood pressure [
17,
18], and the literatures on excessive alcohol consumption’s harmful effects on blood pressure level are also mostly consistent [
19,
20]. However, little is known about the interactive effect of excessive sodium intake and drinking on hypertension in older adults. Therefore, with a view to expanding the present evidence base for the prevention of hypertension and developing future public health interventions in Inner Mongolia, we sought to use Chinese adult chronic disease and nutrition monitoring data to explore the association between the effects of sodium intake and alcohol consumption on hypertension in people over 55 years old in Inner Mongolia, particularly examining whether sodium intake and alcohol consumption have an additive or synergistic impact on hypertension and whether a positive or negative interaction is present.
Discussion
In this cross-sectional study, the standardized prevalence of hypertension was 62.33% among people aged ≥55 years in Inner Mongolia. The previously study reported that the hypertension prevalence was 54.6% in 31 other provinces in China [
28]. Previous work has shown that the risk of hypertension increased with age, and those aged 55–60 years are the most likely to have hypertension [
7]. Moreover, with increasing age, people are more susceptible to chronic depression and declines in body function caused by changes in metabolic status, which may influence the intensity of physical activity after age 55 [
29]. Because of the characteristics of residents of Inner Mongolia who are aged 55 years and older, interventions for the prevention of hypertension should place significantly more emphasis on this population. Both excessive sodium intake and excessive drinking were independently associated with hypertension. Moreover, the combined effect of excessive sodium intake and excessive drinking was associated with the highest risk of hypertension, which suggests that preventive interventions including both sodium reduction and alcohol consumption control are very important.
The present study showed that sodium intake and drinking were both independently related to the risk of hypertension among a representative sample of Inner Mongolia residents. Compared with heavy alcohol consumption, excessive sodium intake was more closely related to hypertension, which was in accordance with other studies [
30]. Our study also confirmed that excessive sodium intake is independently associated with the risk of hypertension. Another study reported that a reduction in adults’ sodium intake decreased systolic blood pressure by 3.39 mmHg, and this change was significant [
31]. The effect of decreasing blood pressure by reducing sodium intake was more pronounced in older adults than in younger subjects. Interestingly, a 12-month follow-up study found that participants older than 55 years who used a salt substitute containing 65% sodium chloride had lower blood pressure than those who consumed normal salt (100% sodium chloride) [
32].
Compared with being a non-drinker, being an excessive drinker was significantly independently associated with an increased risk of hypertension in this study. As was also shown in a previous study, regular alcohol consumption was associated with double the odds of hypertension compared with being a non-drinker [
33]. The Atherosclerosis Risk in Communities cohort study revealed that the risk of hypertension was higher in people who drank more than 210 g of alcohol per week compared with non-drinkers [
34]. However, we did not find a relationship between moderate drinking and hypertension. Even in the multivariate interaction analysis, the effect of moderate drinking on hypertension risk was relatively small. Currently, the impact of light/moderate alcohol consumption on blood pressure is a controversial question. Accordingly, Jaubert and colleagues evaluated the relationship between alcohol consumption and 24-h ambulatory blood pressure in a community-based older adult cohort. After adjusting for relevant covariates, they found that blood pressure was significantly higher in moderate-to-heavy drinkers than in the reference group [
35]. However, the Global Burden of Disease 2016 Alcohol Collaborators found that consuming zero standard drinks daily was associated with the lowest risks in all aspects of health [
11]; in other words, not drinking is the healthiest lifestyle. This suggests that further study is required to explore the effect of moderate alcohol consumption on hypertension.
We also found a significant multiplicative interaction effect of sodium intake and drinking on the risk of hypertension. Individuals who consumed both sodium and alcohol excessively had the highest risk of hypertension, compared with those with moderate sodium intake and no alcohol consumption. Similar to our findings, consuming excessive alcohol and high levels of salted fermented seafood has been found to be associated with significantly elevated rates of pre-hypertension and hypertension in Korean adults [
36]. Participants consuming high levels of alcohol were 3.05 times more likely to be hypertensive than those with low consumption patterns. However, this previous study examined dietary patterns generated using factor analysis and the drinking dietary pattern of consuming alcohol and salted fermented seafood [
36].. A similar study conducted in China found that drinking and dietary patterns focusing on the amount of alcohol and condiments including salt and oil consumed were associated with an increased risk of hypertension [
37]. Alcohol intake was also found to cause significant increases in blood pressure and sodium balance in Japanese men with hypertension in a study by Yuhei and colleagues, which suggests that sodium and alcohol intake may interact with each other; however, this previous study did not clarify the specific mechanism of the interaction [
38]. Salt-sensitive hypertension is common in older adults; in addition, long-term drinking can accelerate the development of hypertension by damaging the renin-angiotensin system and impairing endothelial function, resulting in decreased salt sensitivity. Gennaro and colleagues studied how blood pressure responded to dietary sodium disposal among alcoholics; interestingly, they found that the sodium sensitivity index, which measures the degree of salt sensitivity, was significantly higher in alcoholics, and that blood pressure was significantly elevated [
39]. Another study showed that drinking excessively led to chronic sodium retention and increased intracellular sodium ion concentration, resulting in hypertension [
40].
Consistent with our findings, previous studies have reported significant associations between excessive drinking and blood pressure level at the same level of sodium intake. We also found that, at the same level of drinking, excessive sodium intake was associated with an increased risk of hypertension across all alcohol consumption groups. This suggests that drinking is an influential factor that increases the association of sodium intake with the risk of hypertension.
Inner Mongolia is a multi-ethnic region in the most northern part of China, with large internal variations in geography and climate. Because the annual cold season is longer in this region than in other areas of China, the Inner Mongolia residents’ diet is characterized by lower intake of fresh fruit and vegetables and greater intake of foods containing oil and salt, and excessive drinking is a prevalent habit [
21]. Wine is an essential beverage for social gatherings in Inner Mongolia, and higher alcohol consumption tends to increase energy intake because residents are accustomed to eating pickled food with high salt content when they drink. Our findings indicate that the consistent presence of both excessive sodium intake and heavy drinking greatly increases the risk of hypertension.
Limitations
This study had several limitations. As is the case in all cross-sectional studies, the difficulty of the accurate evaluation of alcohol consumption and the possibility underreporting or over-reporting should be considered. It is likely that any classification or measurement error occurred at random, which may have attenuated the observed findings, leading to an underestimate of effects. Misclassification, particularly for the reporting of alcohol consumption, may have led to an underestimation of the effects of drinking on hypertension risk. Additionally, because this was a cross-sectional study, the causal associations of sodium intake and drinking with the risk of hypertension should be further examined in large cohort studies. Finally, the study sample was small. However, we endeavoured to minimise distortion and generalisation of the data by using statistical tests and sampling methods. Addition research with larger numbers of subjects is required to verify our findings.
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