ABSTRACT
Aim
The association between composite dietary antioxidant index (CDAI) and hypertension remains unknown. Our study was to investigate the association of CDAI with hypertension in general adults.
Methods
A total of 21 526 participants were enrolled from the National Health and Nutrition Examination Surveys (NHANES). The CDAI was calculated from the intake of six dietary antioxidants. Multivariable logistic regressions were performed to explore the associations between CDAI and the prevalence of hypertension. Non-linear correlations were explored using restricted cubic splines. And the inflection point was determined by the two-piecewise linear regression.
Results
In the multivariate logistic regression model with full adjustment for confounding variables, the odds ratio (95% confidence interval) of CDAI associating with hypertension was 0.98 (0.97–1.00; P = .016). Besides, compared to the lowest quartile, the highest quartile of CDAI was associated with a lower risk of hypertension (0.81 [0.70–0.94]; P = .006). Furthermore, a linear association was found by restricted cubic spline, with 3.4 being the turning point.
Conclusion
Our study highlighted a negative linear association between CDAI and hypertension in general adults.
Introduction
Hypertension is one of the leading risk factors for cardiovascular disease (CVD) and premature deaths worldwide (Citation1,Citation2), responsible for 14% of deaths globally (Citation3). The prevalence of hypertension in adults ranges from 32% to 46% in the United States (Citation4). Proper management of hypertension may require both pharmacological and non-pharmacological interventions. Non-pharmacological interventions help reduce the daily dose of antihypertensive medication and delay the progression from prehypertension to hypertension stage (Citation5).
Oxidative stress is an imbalance between reactive oxygen species production and antioxidant defense. Numerous reports have revealed a strong relationship between hyperactive oxidative stress and CVD (Citation6–8). A link between oxidative stress and hypertension has been firmly established in multiple animal models of hypertension (Citation9). Clinical studies have also demonstrated hypertensive patients have decreased antioxidant status. A study suggested that daily dietary intake of antioxidants can reduce oxidative stress by increasing plasma level of antioxidants (Citation10). Adjusting the diet structure may be an effective way to alleviate hypertension by lowering the oxidative stress level within body.The Composite Dietary Antioxidant Index (CDAI) is a valid and reliable nutritional tool to assess overall antioxidant characteristics of the diet, which is a summary score of six dietary antioxidants including vitamins A, C, and E, manganese, selenium, and zinc (Citation11). Previous studies found that higher CDAI was inversely related to the risk of osteoporosis (Citation12), depression (Citation13), cancer (Citation11) and cardiovascular mortality (Citation14). Besides, some reviews reported the relationship between blood pressure and some antioxidants, including vitamin C (Citation15), selenium (Citation16), and zinc (Citation17). To our knowledge, the relationship between CDAI and hypertension has not been evaluated.
In our study, we examine the potential association between CDAI and hypertension, with the aim of controlling hypertension better through dietary guidance.
Methods
Study population
The study included participants from the National Health and Nutrition Examination Survey (NHANES). depicted the selection process of our study. Individuals with missing dietary data (n = 1,720) and hypertension data (n = 648) were excluded from 23 894 adults. Finally, 21526 adults with complete information were included in our analyses. All participants provided written informed consent and the protocol was approved by the Ethics Review Board of National Center for Health Statistics (Protocol #98–12, Protocol #2005–06, and Protocol #2011–17).
Figure 1. The flow chart of participant selection.
Exposure and outcomes
Each participant’s food and nutrient intake in the NHANES dataset was recorded via a 24-h dietary recall interview. The first dietary recall was conducted in person and then 3 to 10 days later via telephone. The Food and Nutrient Database for Dietary Studies of the United States Department of Agriculture was used to calculate the intake of antioxidants, micronutrients, and total energy (Citation18). Based on the questionnaire interview, we determined the intake of dietary supplements during the past month, including dosage, frequency, and duration of consumption (Citation19). Six antioxidants (manganese, selenium, zinc, and vitamins A, C, and E) were standardized by subtracted the mean and divided by standard deviation. Then the CDAI was based on the sum of these standardized consumptions.
Hypertension was defined as the self-report hypertension, or systolic blood pressure ≥140 mmHg, or diastolic blood pressure ≥90 mmHg, or taking antihypertensive drugs.
Covariates
To assess the influence of potential confounding factors, we selected several important covariates, including individual sex, age, race, education level, activity condition, drinker, smoker and total energy, which were collected by using standardized questionnaires. Weight and height of each participant were obtained from the physical examinations. Body mass index (BMI) was defined as weight (kg)/height (m2). Multiple imputation was performed for missing values.
Statistical analysis
Participants were separated into two groups based on whether they had hypertension. Baseline variables differences were tested by Student t test and Chi-Square tests. The relationship between CDAI and hypertension was explored with logistic regression models. Model 1, no covariate was adjusted; Model 2 was adjusted for age and gender. Model 3 added to model 2 the race, education, activity, drinker, smoker, BMI and energy as covariates. The restricted cubic splines were performed to explore the nonlinearity. Then a two-piecewise linear regression model was constructed to calculate the turning point. All statistical analyses were done in R software, version 3.6 and P < .05 was regarded as significant.
Results
The baseline features of participants were summarized in . Within the presence of hypertension, significant differences were observed regarding sex, age, race, education status, activity status, smoking status, BMI, blood pressure, daily energy intake level, and CDAI. The individuals with hypertension were older and female, had lower education but higher BMI, and had lower CDAI scores.
Table 1. Characteristics of the study population based on the presence of hypertension.
Three models were constructed to examine the relationship between CDAI and hypertension in this study (). In Model 1, the odds ratio (OR) and 95% confidence interval (CI) was 0.97 (0.96–0.98; P < .001), which indicated that the risk of hypertension was reduced for every unit rise in CDAI. The relationship still existed in the model 2 (OR [95% CI]: 0.99 [0.98–1.00]; P = .019) and model 3 (OR [95% CI]: 0.98 [0.97–1.00]; P = .016).
Table 2. Association of composite dietary antioxidant index and hypertension.
Restricted cubic spline suggested the relationship between CDAI and hypertension was linear (P for nonlinearity = 0.124; ). A threshold effect analysis of CDAI on hypertension was further performed by the two-piecewise linear regression. As shown in ; , the inflection point was 3.4. Each unit increase of CDAI was associated with a 3% decrease of the risk of hypertension below 3.4, and the relationship was not statistically significant above 3.4.
Figure 2. The dose-response relationship (A) and the two-piecewise linear regression (B) between CDAI and the prevalence of hypertension.
Table 3. Threshold effect analysis of composite dietary antioxidant index on hypertension by the two-piecewise linear regression.
We added a sensitive analysis on the association of six components of CDAI and hypertension. As shown in , after adjusting for all variables, only vitamins E (OR [95% CI]: 0.93 [0.88, 0.98]; P = .005) and manganese (OR [95% CI]: 0.92 [0.86, 0.97]; P = .005) were independently associated with the presence of hypertension. In addition, due to a large gender difference, we made a sensitive analysis according to gender status. As shown in , the association was consistent across gender statues (P for interaction = 0.216).
Table 4. Association of six components of composite dietary antioxidant index and hypertension.
Table 5. Association of composite dietary antioxidant index and hypertension according to gender status based on Model 3.
Discussion
In our study, we found that CDAI was negatively associated with hypertension. And the relationship remained even after adjusted other covariates, which indicated that CDAI was a protective factor for the development of hypertension. A dose-response analysis found that this negative correlation was linear. Threshold effect analysis suggested that the inflection point was 3.4.
Although existing research on the relationship between CDAI and hypertension is still relatively rare, the use of dietary antioxidant properties to intervene hypertension has been a hot topic of research today. A study showed a higher dietary total antioxidant capacity was associated to a decreased odd of hypertension in Iranian Kurdish women (Citation20) and French men (Citation21). A study found that an antioxidant-rich dietary intervention for 4 weeks improved the components of metabolic syndrome in Koreans elderly, including central obesity, dyslipidemia, hypertension, and arterial stiffness (Citation22). Results from NHANES also suggested that dietary carotenoids, an important antioxidant, were inversely associated with hypertension in US adults (Citation23). In line with previous studies, our results also confirmed a negative correlation between CDAI and hypertension.
Further analysis showed that vitamins E and manganese were inversely related to hypertension. A prospective cohort study found a reverse J-shaped association between dietary vitamin E intake and new-onset hypertension in Chinese adults (Citation24). While a Spain study revealed no significant association between them (Citation25). Therefore, the relationship may be influenced by different ethnicities. Several meta-analyses confirmed that magnesium supplementation had a beneficial effect on blood pressure lowering (Citation26–28).
There is abundant evidence that there is gender/sexual dimorphism in the incidence and regulation of blood pressure in humans and experimental animal models, respectively (Citation29). Male spontaneous hypertension rat (SHR) have higher levels of oxidative stress that contribute to their hypertension than females, and thus one would expect that antioxidants would cause a better depressor response in males than in females (Citation30). However, our study found that the inverse correlation remain consistent across gender status.
The mechanism may be closely related to oxidative stress. Hypertensive patients have been reported to have higher oxidative stress and inflammation levels (Citation31,Citation32). Manganese and Zinc is important components of antioxidant mitochondrial metalloenzymes (MnSOD, ZnSOD) (Citation33). Selenium is bound to selenoproteins and prevents lipid peroxidation and oxidative cell damage (Citation34). Non-enzymatic antioxidants such as vitamins A, C, and E play an important role in reducing stress-induced changes in oxidants (Citation35). Therefore, antioxidant nutrients from food may be able to prevent the onset of hypertension caused by oxidative stress.
However, the exact molecular mechanisms are not well-understood, and more research is needed.
There are several limitations to this study. Firstly, the diet assessment might involve measurement errors and inaccuracies. Secondly, bias is inevitable in cross-sectional studies.
Conclusion
Our study found a linear negative association between CDAI and hypertension in the adult population, after being adjusted for potential confounders. In the future, additional randomized controlled trials or cohort studies are urgently needed to confirm this finding to provide more accurate and effective prevention and treatment options for depression prevention.
Ethics approval and consent to participate
The protocol was approved by the Institutional Review Board of National Center for Health Statistics and no new data was added.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
All data could be available upon request from the corresponding author.
Additional information
Funding
References
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