Introduction
The WHO reports that approximately 1·3 billion people aged 30–79 years have hypertension(1). Hypertension is a major risk factor for CVD and early death(1,Reference Kjeldsen2) , and thus, its prevention and control are vital. Diet is a crucial, modifiable risk factor for hypertension(3). In 1997, the National Heart, Lung, and Blood Institute in the USA developed the Dietary Approaches to Stop Hypertension (DASH) diet that was aimed at reducing blood pressure (BP)(Reference Appel, Moore and Obarzanek4). Many previous studies have confirmed the BP-controlling effect of the DASH diet, and it has been proven to be one of the most effective diets for hypertension control(Reference Schwingshackl, Chaimani and Schwedhelm5).
The DASH diet promotes increased potassium intake through higher consumption of fruits and vegetables(Reference Suri, Kumar and Kumar6). Additionally, it promotes enhanced Mg, Ca and dietary fibre consumption, as these are inversely associated with high BP(Reference Appel, Moore and Obarzanek4). Although Na plays a critical role in BP regulation by increasing water retention to maintain homeostasis, consequently leading to an increase in BP(Reference Aung, Ream-Winnick and Lane7), the original DASH diet did not explicitly include Na restriction(Reference Appel, Moore and Obarzanek4). Instead, it expects the potassium in vegetables and fruits to promote Na excretion(Reference Staruschenko8).
However, individuals with dental issues(Reference Nakamura, Ojima and Nagahata9) or those from lower socio-economic backgrounds(Reference Amini, Najafi and Kazemi Karyani10) may face challenges in consuming the recommended quantities of vegetables and fruits. In such scenarios, the effectiveness of potassium in Na control might be compromised. In addition, Na intake is recommended to be limited to ≤2300 mg or 1500 mg when following the DASH diet(11,Reference Challa, Ameer and Uppaluri12) . Therefore, integrating Na restriction with the DASH diet could be beneficial in managing BP, especially among older adults, who tend to consume more salt owing to diminished taste sensitivity(Reference Sato, Wada and Matsumoto13). Specifically, a Na-restricted DASH diet might have a more pronounced impact on BP management in hypertension patients.
The BP control effects of both the DASH diet and Na restriction have been systematically and independently reviewed(Reference Schwingshackl, Chaimani and Schwedhelm5,Reference Filippou, Tsioufis and Thomopoulos14) . However, to our best knowledge, there has been no systematic attempt to review and identify interventions that combine Na restriction with the DASH diet for BP control. Thus, this study aimed to address this gap by systematically reviewing and elucidating the characteristics and BP control effects of interventions that combine a Na-restricted DASH diet.
Methods
This systematic review was conducted following the Cochrane Handbook for Systematic Reviews of Interventions(Reference Higgins, Thomas and Chandler15). This study was reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guideline(Reference Page, McKenzie and Bossuyt16) and the Synthesis Without Meta-Analysis guideline(Reference Campbell, McKenzie and Sowden17). The study protocol was registered with PROSPERO (ID: CRD42023409996).
Search strategy and study selection
The following nine databases were searched between April and May 2023: MEDLINE, Embase, Cochrane Central Register of Controlled Trials, CINAHL, Scopus, KoreaMed, KISS, KMbase and RISS. ClinicalTrials. Gov, Grey Literature Report, OpenGrey and PQDT Global were also searched to include grey literature. The search strategy was established using the Boolean operators ‘OR’ and ‘AND’ to combine keywords related to ‘dietary approaches to stop hypertension’ and ‘sodium restriction’. Index terms of the databases and free-text terms were used to establish the search strategy (online Supplementary Table 1), which a librarian reviewed before the search. We limited the language of the studies to English and Korean without limiting the publication year. The Population, Intervention, Comparison, Outcome and Study (PICOS) frames used are presented in Table 1.
Table 1. The PICOS of the study
DASH, dietary approaches to stop hypertension.
EndNote 20 (Clarivate Analytics) was used to import studies and remove duplicates. The studies were independently selected by two researchers (SK and HJ) based on the eligibility criteria and PICOS. Disagreements between the researchers were resolved through discussions to reach a consensus. The initial screening included screening the titles and abstracts of the articles for eligibility. Full articles were retrieved and read to evaluate their eligibility. The eligibility criteria of this study were as follows: (1) randomised controlled trials evaluating the BP-controlling effect of the Na-restricted DASH diet in adults (age ≥ 18 years), except in pregnant women as gestational hypertension has a different pathophysiology from general hypertension(Reference Braunthal and Brateanu18), and (2) studies for which the full article can be retrieved.
Data extraction and analysis
Two researchers (SK and HJ) autonomously extracted the data from the included studies using a data extraction form. Disagreements were resolved through discussions and joint reviews of the original articles. The extracted data included publication characteristics (authors, journals and year of publication), study characteristics (country, sample size, age, sex, race and hypertension status), intervention content (amount of Na restriction, details of the intervention, intervention setting and duration of intervention) and outcome (BP before and after intervention). Hypertension status was categorised as ‘elevated BP’ or ‘hypertension’ according to the 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline(Reference Whelton, Carey and Aronow19). Elevated BP was defined as systolic blood pressure (SBP) ranging from 120 mmHg to 129 mmHg and diastolic blood pressure (DBP) under 80 mmHg(Reference Whelton, Carey and Aronow19). However, hypertension was defined as SBP ≥ 130 mmHg or DBP ≥ 80 mmHg(Reference Whelton, Carey and Aronow19).
When the BP was measured multiple times, we included the results obtained in the clinical setting in the analysis to consider the accuracy of the results. A narrative summary of the included studies was created based on the extracted data. Considering that the intervention types differed among the included studies, the results of the studies were also compared based on the intervention types. Nevertheless, if there were more than two groups in the included studies, we combined the groups that applied the Na-restricted DASH diet as the intervention group and the groups without the Na-restricted DASH diet as the comparator for the analysis. Furthermore, the effect sizes of the included studies on BP control were calculated using the mean difference, and a box-and-whisker plot was drawn. Additionally, evidence certainty was evaluated using the Grading of Recommendations, Assessment, Development and Evaluations approach through GRADEpro GDT (McMaster University and Evidence Prime).
Risk of bias assessment
The risk of bias in each included study was independently evaluated by two researchers (SK and HJ) using the Risk of Bias 2·0(Reference Sterne, Savović and Page20). Researchers followed the Risk of Bias 2·0 algorithm to assess the risk of bias by answering the questions for five domains (bias arising from the randomisation process, bias due to deviations from intended interventions, bias due to missing outcome data, bias in the measurement of the outcome and bias in the selection of the reported result)(Reference Sterne, Savović and Page20). Each question was answered by ‘yes (Y)’, ‘probably yes (PY)’, ‘no (N)’, ‘probably no (PN)’ and ‘no information (NI)’. Any disagreements in the decision for each question between researchers were addressed through discussion. Additionally, each domain was rated as ‘low risk of bias’, ‘some concerns’ and ‘high risk of bias’, followed by a rating of the overall risk of bias(Reference Sterne, Savović and Page20).
Results
Selected studies
A total of 4819 articles were identified through a comprehensive search, with 2793 found to be duplicates. After reviewing the titles and abstracts of the remaining 2026 articles, 1939 articles were excluded because of irrelevance. Among the remaining eighty-seven articles, twenty-two were further excluded due to the unavailability of the full articles. A full-text review was conducted on the remaining sixty-five articles, and fifty-six articles were excluded due to unrelatedness. Ultimately, nine studies(Reference Appel, Champagne and Harsha21–Reference Zou, Dennis and Lee29) fulfilled our inclusion criteria and were included in the systematic review (Fig. 1).
Fig. 1. Preferred Reporting Items for Systematic Reviews and Meta-Analysis 2020 flow diagram.
General characteristics of the included studies
The included studies were published between 2001 and 2022. Four studies were conducted in the USA, and five studies were conducted in Australia, Canada, Greece, Japan and Pakistan. The number of participants ranged from 25 to 1700, with a total of 3412. However, 398 participants were excluded from the final analysis owing to loss to follow-up or compliance issues. The average participant age was 52·1 years. One study included only menopausal females(Reference Nowson, Wattanapenpaiboon and Pachett25), while another included males and females. Among the nine studies, only three included Asians(Reference Naseem, Ghazanfar and Assad24,Reference Umemoto, Onaka and Kawano27,Reference Zou, Dennis and Lee29) , and three studies included diverse races(Reference Appel, Champagne and Harsha21,Reference Miller, Erlinger and Young23,Reference Sacks, Svetkey and Vollmer26) . Furthermore, one study targeted African Americans(Reference Whitt-Glover, Hunter and Foy28), and the last two studies did not identify the race of the study participants(Reference Kirpizidis, Stavrati and Geleris22,Reference Nowson, Wattanapenpaiboon and Pachett25) . All studies included participants with hypertension or elevated BP (Table 2).
Table 2. Publication and general characteristics of the included studies (n 9)
I, intervention; C, control; sd, standard deviation; E, established; DASH, dietary approaches to stop hypertension; M, male; F, female; BP, blood pressure; NI, no information; J, J-DASH (Japanese cuisine-based DASH).
Intervention characteristics of the included studies
The amount of Na restriction varied among the nine studies, ranging from approximately 1150 to 3100 mg (Table 3). Notably, three studies employed multiple standards of Na restriction(Reference Kirpizidis, Stavrati and Geleris22,Reference Sacks, Svetkey and Vollmer26,Reference Zou, Dennis and Lee29) . In one study, three different Na restriction amounts were applied to all participants in random order during the intervention(Reference Sacks, Svetkey and Vollmer26). In contrast, another study adjusted three different Na restriction amounts based on the participant’s age(Reference Zou, Dennis and Lee29). However, one study did not identify how the two different amounts of Na restriction were applied(Reference Kirpizidis, Stavrati and Geleris22).
Table 3. Summary of intervention and the result of the included studies (n 9)
SBP, systolic blood pressure; DBP, diastolic blood pressure; DASH, dietary approaches to stop hypertension; J, J-DASH (Japanese cuisine-based DASH); NI, no information; E, stablished; HCP, healthcare provider.
* The effect sizes are calculated by comparing the control group and the combined group of J-DASH 1 and J-DASH 2 groups.
† The effect sizes are calculated by comparing the established + DASH group and the combined group of the control and established groups.
We classified the Na-restricted DASH diet interventions in the included studies into three categories: feeding, menu or food item provision and education. Three studies conducted feeding interventions in which the researchers provided meals to the participants(Reference Miller, Erlinger and Young23,Reference Nowson, Wattanapenpaiboon and Pachett25,Reference Umemoto, Onaka and Kawano27) , while the other three provided weekly menus or food items to the participants(Reference Kirpizidis, Stavrati and Geleris22,Reference Naseem, Ghazanfar and Assad24,Reference Nowson, Wattanapenpaiboon and Pachett25) . Additionally, another three offered lectures and counselling to the participants(Reference Appel, Champagne and Harsha21,Reference Whitt-Glover, Hunter and Foy28,Reference Zou, Dennis and Lee29) . The intervention duration ranged from 5 weeks to 6 months.
Outcome characteristics of the included studies
BP was the outcome variable in the included studies. The frequency and methods used to measure BP varied among the studies. All studies conducted pre- and post-intervention BP measurements, while five studies also assessed BP during the intervention at least once(Reference Appel, Champagne and Harsha21,Reference Kirpizidis, Stavrati and Geleris22,Reference Nowson, Wattanapenpaiboon and Pachett25,Reference Sacks, Svetkey and Vollmer26,Reference Whitt-Glover, Hunter and Foy28) . Except for one study that did not specify the setting of BP measurement(Reference Whitt-Glover, Hunter and Foy28), the remaining eight studies measured BP in a clinical setting using manual or digital sphygmomanometers. The methods of BP measurement are detailed in online Supplementary Table 2. One study additionally measured 24-h ambulatory BP(Reference Miller, Erlinger and Young23). Furthermore, two studies also asked their participants to measure BP at home(Reference Nowson, Wattanapenpaiboon and Pachett25,Reference Umemoto, Onaka and Kawano27) . A single study conducted a follow-up BP measurement 4 months post-intervention(Reference Umemoto, Onaka and Kawano27).
All intervention groups exhibited a decrease in BP following the intervention. However, only three studies revealed significantly lower BP in the intervention group than in the control group(Reference Naseem, Ghazanfar and Assad24,Reference Sacks, Svetkey and Vollmer26,Reference Umemoto, Onaka and Kawano27) (Table 3). The analysis of study outcomes relative to the type of intervention was conducted as follows. Among the three feeding studies, two studies demonstrated significantly lower BP compared with the control group(Reference Sacks, Svetkey and Vollmer26,Reference Umemoto, Onaka and Kawano27) . In the study by Sacks et al. (Reference Sacks, Svetkey and Vollmer26), the implementation of a DASH diet coupled with a 50 mmol Na restriction led to a reduction in both SBP and DBP, surpassing the control group that adhered to an American diet with a 150 mmol Na limitation(Reference Sacks, Svetkey and Vollmer26). Umemoto et al. (Reference Umemoto, Onaka and Kawano27) explored two distinct intervention groups: the Japanese cuisine-based DASH 1 group and the Japanese cuisine-based DASH 2 group, which varied in the frequency of DASH diet application. Both intervention groups exhibited a more pronounced BP reduction than the control group(Reference Umemoto, Onaka and Kawano27).
In the context of menu or food item provision studies, Naseem et al. (Reference Naseem, Ghazanfar and Assad24) observed a greater SBP decrease in the intervention group, whereas Nowson et al. (Reference Nowson, Wattanapenpaiboon and Pachett25) found no significant differential effect. Kirpizidis et al. (Reference Kirpizidis, Stavrati and Geleris22) did not clarify the differences among groups. Furthermore, two educational intervention studies failed to show significant differences between the intervention and control groups(Reference Whitt-Glover, Hunter and Foy28,Reference Zou, Dennis and Lee29) . Appel et al. (Reference Appel, Champagne and Harsha21) implemented an educational intervention and involved three distinct groups: the advice-only group, the established group implementing lifestyle changes, including Na restriction, and the established + DASH group, which combined lifestyle changes with a DASH diet. The established + DASH group experienced a higher reduction in both SBP and DBP than did the advice-only group(Reference Appel, Champagne and Harsha21). However, the difference was not significant when compared with the established group(Reference Appel, Champagne and Harsha21).
The effect sizes varied across the included studies. Notably, calculating the mean difference in BP by Sacks et al. (Reference Sacks, Svetkey and Vollmer26) was not feasible because the participants in their study had different orders of Na restriction. Consequently, this study was excluded from effect size calculations. The box-and-whisker plot constructed based on the effect sizes of the remaining eight studies is shown in Fig. 2. The effect size of the SBP ranged from −7·70 to −2·40 (median: −3·70; 95 % CI −5·76, −2·92). The effect size of the DBP ranged from −8·30 to 0·10 (median: −2·95; 95 % CI −5·60, −1·66).
Fig. 2. Box-and-whisker plot of the effect sizes.
Risk of bias
For the risk of bias assessment using the Risk of Bias 2·0, six out of nine included studies showed a high risk of bias(Reference Appel, Champagne and Harsha21,Reference Naseem, Ghazanfar and Assad24–Reference Sacks, Svetkey and Vollmer26,Reference Zou, Dennis and Lee29) (Fig. 3). Additionally, the remaining three studies had some concerns regarding the risk of bias(Reference Kirpizidis, Stavrati and Geleris22,Reference Miller, Erlinger and Young23,Reference Umemoto, Onaka and Kawano27) . Particularly, the selection of reported results showed the greatest risk of bias.
Fig. 3. Summary of the risk of bias of included studies.
Evidence certainty
The results of the evidence certainty assessment according to the Grading of Recommendations, Assessment, Development and Evaluations approach are presented in Table 4. Owing to the generally high risk of bias among the included studies, the certainty of the evidence was low for SBP and DBP.
Table 4. Grading of Recommendations, Assessment, Development and Evaluations (GRADE) certainty assessment
SBP, systolic blood pressure; RCT, randomised controlled trials; DBP, diastolic blood pressure.
GRADE Working Group grades of evidence. High certainty: We are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: We are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: Our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: We have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.
* Overall, six of nine studies are assessed as having a high risk of bias. The other three studies had some concerns for the risk of bias.
Discussion
We conducted a systematic review to comprehensively examine the characteristics and BP-controlling effects of Na-restricted DASH dietary interventions. Despite the BP reduction observed in all the intervention groups after applying the Na-restricted DASH diet, feeding interventions showed a greater effect on BP control than the control interventions. Our findings demonstrated that feeding interventions were more effective in controlling BP than provisional or educational interventions. This result might be because it was easier and more convenient for participants to comply with the feeding interventions than provisional or educational interventions. Although the participants in provisional or educational studies needed to prepare their meals, those in feeding studies had their meals provided by researchers. Therefore, participants in the feeding studies did not require extra time or effort to prepare meals or purchase food items from a Na-restricted DASH diet, potentially leading to higher adherence. Given that high adherence to the DASH diet correlates directly with BP reduction(Reference Theodoridis, Triantafyllou and Chrysoula30), high adherence to the Na-restricted DASH diet may also correlate directly with BP reduction.
Furthermore, the precise delivery of nutrients in feeding studies could contribute to the greater effectiveness of BP reduction. This aligns with a previous study where participants in a feeding study had better-quality meals and the amount they ate was more accurate(Reference Wing and Jeffery31). Given that researchers prepare meals for participants in feeding interventions, food and Na could be delivered in the amount planned by the researchers. Conversely, the amount of nutrients consumed in provisional or educational studies could be inaccurate. The intervention duration (2–3 months) may also contribute to the greater BP control effect of the feeding interventions. In intervention studies, delivering an intervention for more than 8 weeks is recommended to avoid novelty effects(Reference Clark, Sugrue and Anglin32). However, if the intervention period is too long, the dropout rate and the risk of being affected by other distributing factors may likely increase(Reference Cooper and Conklin33,Reference Skelly, Dettori and Brodt34) .
Our results show that only one of the three provisional studies showed a significant BP reduction when compared with the values of the control group(Reference Naseem, Ghazanfar and Assad24). The inconsistent results of the included provisional studies may be attributed to improper control interventions and diverse study designs. Naseem et al. (Reference Naseem, Ghazanfar and Assad24), who reported a significant reduction in SBP, encouraged the control group to maintain their usual diet. Conversely, Nowson et al. (Reference Nowson, Wattanapenpaiboon and Pachett25) offered low-fat diet food items to the control group and found no difference in BP reduction between groups. This could be because a low-fat diet also decreases BP(Reference Wilde, Massey and Walker35), although the BP of the intervention group was considerably decreased. Kirpizidis et al. (Reference Kirpizidis, Stavrati and Geleris22) had a different study design. However, they did not compare the intervention and control groups after the intervention and instead measured the changes in BP in both groups. They reported that both intervention and control groups showed a significant reduction in BP after the interventions.
In contrast, the educational interventions included in our study did not show an apparent BP control effect. Previous studies have reported that personal factors (e.g. attitude towards diet) and environmental factors (e.g. the accessibility or affordability of food items) are crucial in changing dietary behaviour(Reference Deslippe, Soanes and Bouchaud36). The lack of significant reduction in BP in the studies by Appel et al. (Reference Appel, Champagne and Harsha21) and Zou et al. (Reference Zou, Dennis and Lee29) may be attributed to their exclusive focus on personal factors in the interventions. However, another study did not show a BP-lowering effect, although it included environmental factors in the intervention by providing information about budgeting and grocery shopping(Reference Whitt-Glover, Hunter and Foy28). We do not know why Whitt-Glover et al. (Reference Whitt-Glover, Hunter and Foy28), who included both personal and environmental factors, did not find a positive effect on reducing BP. Education alone might not have been sufficient to change dietary behaviour.
Although our study results indicated that the Na-restricted DASH diet might lower BP, previous systematic reviews reported differing results(Reference Filippou, Tsioufis and Thomopoulos14,Reference Guo, Li and Yang37) . These discrepancies may be attributed to several factors. First, in Filippou et al. (Reference Filippou, Tsioufis and Thomopoulos14), ten of the twenty-three studies were of low quality. Additionally, in Guo et al. (Reference Guo, Li and Yang37), two of the five studies exhibited a high risk of bias, while the remaining three also raised some concerns about bias. Therefore, the low quality of the included studies and the risk of bias may have contributed to the disparate findings. Second, intervention types might have influenced the result. Filippou et al. (Reference Filippou, Tsioufis and Thomopoulos14) did not report the intervention types of the included studies. Conversely, Guo et al. (Reference Guo, Li and Yang37) included only one feeding study in the analysis. Considering our finding that the Na-restricted DASH diet demonstrated a conspicuous BP-controlling effect in feeding studies, this discrepancy in results might be due to the limited representation of feeding studies in the previous analyses.
Regrettably, only one long-term study has been identified(Reference Umemoto, Onaka and Kawano27). It is crucial to ascertain if the impact of an intervention endures beyond the intervention period rather than merely the immediate effect post-intervention(Reference Walugembe, Sibbald and Le Ber38). A prior study demonstrated that the DASH diet sustained its BP control effect for up to 8 months following the intervention(Reference Hinderliter, Sherwood and Craighead39). In addition, a study that implemented a mindfulness and DASH diet intervention showed a greater systolic BP reduction in the intervention group than in the non-hypertensive educational group even a month after the intervention(Reference Wright, Klatt and Adams40). Additionally, Juraschek et al. (Reference Juraschek, Woodward and Sacks41) observed that a gradual reduction in Na intake consistently lowered BP over a 4-week period. Given these findings, implementing follow-up BP measurements at least once after a month of interventions could have confirmed the BP control efficacy of the Na-restricted DASH diet rather than relying solely on assessments conducted immediately post-intervention.
There were some limitations in our systematic review. First, six of the nine studies showed a high risk of bias(Reference Appel, Champagne and Harsha21,Reference Naseem, Ghazanfar and Assad24–Reference Sacks, Svetkey and Vollmer26,Reference Zou, Dennis and Lee29) , and the other three studies similarly showed some concerns(Reference Kirpizidis, Stavrati and Geleris22,Reference Miller, Erlinger and Young23,Reference Umemoto, Onaka and Kawano27) . Therefore, the overall high risk of bias served as a critical factor preventing the performance of a meta-analysis. Additionally, it was a key determinant in establishing the certainty of evidence as ‘low’ in the Grading of Recommendations, Assessment, Development and Evaluations certainty assessment. Therefore, the results should be interpreted with caution. Second, we could not conduct a meta-analysis because of the high heterogeneity among the included studies. A meta-analysis presupposes homogeneity of studies regarding participants, interventions, comparators and results(Reference Higgins, Thomas and Chandler15). Nevertheless, the studies included in our study varied in intervention type, duration, restricted Na intake and comparators. Therefore, we could not confirm the presuppositions of the meta-analysis. Third, we limited the publication language to English and Korean. Therefore, there is a possibility that we might have omitted pertinent studies. Therefore, our study findings should be interpreted and applied with caution.
Although there are limitations to the study results, to the best of our knowledge, this is the first attempt to systematically review the characteristics of a Na-restricted DASH diet and its BP-lowering effect. Further high-quality research on the Na-restricted DASH diet is required to address the limitations of the included studies. First, we suggest mitigating the high risk of bias by thoroughly reporting all measured outcomes to improve the quality of future research. Second, we recommend that future researchers consider including a control group with the usual diet when implementing other BP-lowering diets in the control group. This approach may better elucidate the BP-lowering effect of the Na-restricted DASH diet. Once sufficient high-quality research has been accumulated, a meta-analysis should be conducted to integrate the BP-lowering effects of a Na-restricted DASH diet. Third, participants in the included studies had hypertension or elevated BP. Given that the DASH diet has a preventive effect on hypertension(Reference Theodoridis, Chourdakis and Chrysoula42), it is also necessary to test the preventive effect of a Na-restricted DASH diet. Therefore, we recommend including normotensive participants in future studies. Lastly, for future research on the Na-restricted DASH diet, follow-up BP measurements should be conducted after the intervention to assess its long-term effect on BP. Considering that feeding interventions proved more effective than other types of interventions, adopting a Na-restricted DASH diet may be beneficial under specific circumstances for lowering BP, particularly in hypertension patients in hospitals or nursing homes.
Conclusion
The findings indicate that the Na-restricted DASH diet has a more significant BP-lowering effect, particularly in feeding studies, than provisional or educational interventions. Nonetheless, the substantial risk of bias and heterogeneity in the included studies prevented conducting a meta-analysis. Furthermore, our findings have low reliability owing to the generally high risk of bias. However, this systematic review aimed to delineate the attributes of the Na-restricted DASH diet and its effects on BP reduction, striving to provide the best evidence through systematic review.
Acknowledgements
This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
S. K.: formulating the research questions, designing the study, carrying out the study, analysing the data, interpreting the findings and writing the article. H. N. J.: designing the study, carrying out the study and writing the article. S. C.-K.: formulating the research questions and writing the article.
The authors declare that there are no conflicts of interest.
Data described in this manuscript are available in the included articles. This article is a revision of the first author’s doctoral dissertation from Seoul National University.
Supplementary material
For supplementary materials referred to in this article, please visit https://doi.org/10.1017/S000711452400103X.
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