Self-reported diet management, dietary quality, and blood pressure control in Korean adults with hypertension

Hypertension is a global health problem. The prevalence of hypertension worldwide was 26% in 2000, and the total number of adults with hypertension will reach an estimated 1.56 billion in 2025 [1]. Elevated blood pressure (BP) is a leading cause of cardiovascular diseases, disability, and premature death [2, 3]. Along with population ageing, the burden of hypertension on our societies is predicted to increase continuously. However, hypertension is modifiable [4‐7]; and well-controlled BP can prevent clinical complications, enhance quality of life, and improve prognosis [8‐11].

The optimal BP for adults with hypertension can be achieved through pharmacological treatment and nonpharmacological interventions. Daily preventive practices of the affected individual are essential for BP control [12]. During the past decades, the hypertension treatment rate has increased remarkably, especially in some countries including South Korea; and the BP control rate among hypertensive adults treated with medication has also substantially improved [13, 14]. The reason for this may be that self-management of medication has become easier with alleviation of potential barriers surrounding pharmacological treatment, i.e., limited health care, drug expense, inconvenience of dosing, and severity of side effects [15]. However, recent indices of hypertension management have remained stable; and a considerable number of medicated adults with hypertension do not reach the optimal BP control level [14].

Lifestyle modifications such as healthy diet, low sodium consumption, sufficient physical activity, and limited alcohol consumption have been strongly recommended for all hypertensive individuals. These modifications can serve as an initial treatment before the start of medication or as an adjunct to medication in persons already on pharmacological treatment [16, 17]. There are few studies focusing on hypertensive individuals’ lifestyle management practices and their effects on BP control. According to some previous studies, adherence to lifestyle modification, particularly dietary modification, is much lower than that of medication compliance [18, 19]. This is true despite the noted beneficial impact of lifestyle modification in many clinical trials and epidemiologic studies. Contrary to pharmacological treatment, lifestyle modification has few or no harmful side effects and leads to improved overall cardiovascular health in addition to BP reduction [5]. Lifestyle modification can reduce the requirement for BP-lowering drugs [6]. Therefore, a more aggressive movement from pharmacological treatment toward lifestyle modification seems necessary.

To the best of our knowledge, there are few studies that evaluate dietary management practices and their effects on BP control among adults diagnosed with hypertension. Thus, we aimed to investigate the association of self-reported dietary management, dietary quality, and BP control among Korean adults with known hypertension.

This study examined the associations of self-reported diet management practice, dietary quality based-on food and nutrient intakes, adherence to the diet guidelines with BP control among Korean adults with known hypertension. We found that a high-quality diet had a positive association with controlled BP, which was significant only in men.

BP is continuously affected by environmental factors such as diet and physical activity. Prominent effects of diet on BP regulation have been widely identified through numerous epidemiologic studies and clinical trials [4, 5, 7, 23]. A high-quality diet, such as a Mediterranean diet and a diet with a higher HEI score, can prevent development of hypertension in normotensive individuals and can further lower BP in hypertensive individuals already on antihypertensive medication. High-quality diets also reduce cardiovascular risks other than BP [4, 5, 23, 24]. In our study, both diet-managing men and women had higher KHEI scores compared with non-managing individuals and also a higher adherence to the diet recommended for hypertension. Thus, we expected that self-reported diet management practice and high-quality diet would have beneficial effect on BP control. But, the favorable effect of diet was only found in men with borderline significance, and not in women.

In general, women are known to have lower BP levels and higher BP control rates compared with men [25‐27]. These results are from the studies of general populations that included normotensive individuals and hypertensive patients together or from studies that included younger adults. In those studies, the higher BP control rate among women was attributed to women’s higher awareness of their health condition, more frequent health service use, more regular medication, a higher therapeutic adherence, and less risky behaviors [25, 26]. However, other studies especially of older populations and/or individuals with hypertension have reported that women’s BP control rates are similar to or lower than men’s [27, 28]. This was consistent with our findings.

According to previous studies, while overall BP levels differ by sex, there was no difference in the benefit of antihypertensive treatment for individuals with hypertension. Also, there was no difference in the impact of dietary modification on BP changes between the sexes according to previous studies [5, 29, 30]. However, several studies have reported sex differences in BP control even when considering potential factors for BP control such as age, co-morbidity, and antihypertensive medication [28, 31]. In a study of older adults with hypertension, women had much higher BP and poorer BP control rates compared with their male counterparts after adjustment for possible factors of BP regulation [28]. Similar to the results of previous studies, older women with known hypertension in our study had a poorer BP control than older men, and no beneficial impact of dietary management practice and dietary quality was found in women. This finding remained unchanged after adjusting for potential confounding variables such as age, comorbidities, health-related behaviors, and BP-lowering drug use. This was also demonstrated in subgroup analysis according to the presence of antihypertensive medication. We cannot definitely explain the lack of a favorable effect of dietary management on BP control in women. Other factors other than age, co-morbidities, obesity, or socio-demographics may explain sex differences in BP control. This was suggested in a previous study [28]. One possible explanation is that women may need a much more aggressive dietary change to obtain a visible dietary impact on BP control. Young women typically have lower BP than young men. However, with advancing years, their BPs are no different from those of men of the same age; and various advantages in women’s BP regulation may decreased with aging. Previous studies suggested that menopausal women, in addition to having sex hormone profile changes, have increased salt sensitivity due to aging compared with men and young women [32, 33]. Thus, a diet much lower in sodium may be more effective in BP reduction in these older women. Although diet-managing women in our study consumed less dietary sodium and much higher-quality diets than non-managing women, the average intake of dietary sodium in both groups was over the recommended amount for hypertensive patients. Hence, dietary quality may not be enough to expect an impact on BP control. Another possible explanation for the sex differences is that health issues due to aging and sex-specific conditions differ between men and women. The magnitude of the negative effects of these issues and conditions may be greater in women. At young age, women generally have fewer unhealthy behaviors compared with men. However, with aging, women have more cardiovascular risks caused by rapid change in body composition, resulting in poor BP control [34]. Moreover, an imbalance between androgens and female sex hormones, especially the loss of estrogen, among postmenopausal women may increase sympathetic activity and adrenergic vasoconstrictor responsiveness, resulting in BP increase [35]. In recent studies, sex-specific effects on T-cell activation and differentiation have been suggested as a potential mechanism in BP regulation [36]. In summary, detrimental changes followed by both chronological and/or ovarian aging of women make BP control difficult. A third possible explanation is the location at which BP was measured. In our study, BP was measured in an office. This may not be sufficient to assess the BP status of women. A previous study suggested that, in women, office-based BP measurements were much higher than 24-h ambulatory measurements [37]. This creates the possibility of underestimation of BP control. Another possible explanation is that diet-managing men in our study had distinctly better health behaviors (less smoking, less drinking, and more walking) compared with non-managing men, while such a tendency was weak in women. In addition, the prevalence of dietary management was lower in women on antihypertensive medication. These findings may result in different associations of diet with BP control between the sexes.

Among the three diet indicators, which were used in this study, only dietary quality was significantly associated with BP control. These results are partly explicable. In our study, the dietary management practice was defined solely on the basis of self-report. Patients who think they are good at dietary management may actually have a poor-quality diet. This suggests that it is necessary to improve the quality of the actual diet, rather than the diet management practice evaluated by oneself.

Our study had several strengths. Use of the KNHANES data ensures that our study includes a number of hypertensive individuals of diverse backgrounds, such as region and socioeconomic status. We could also analyze vast quantities of data to examine self-reported dietary management, quality, and adherence and BP control. To the best of our knowledge, this is the first study to investigate an association between self-reported practices and their quality and BP control in hypertensive individuals.

Several limitations also should be considered. First, the KNHANES is a cross-sectional survey. Thus, our findings do not support a causal relationship between diet and BP control. Second, our study may not have enough statistical power to carry out sex-specific analysis, although the study sample size is not so small. Meaningful interpretations were difficult for some results, because they had only borderline level of statistical significance. For instance, diet-managing men had a higher possibility of having controlled BP than men non-diet-managing men with borderline significance (OR: 1.27, 95% CI: 0.98–1.66, p-value = 0.07). Third, we evaluated dietary quality and adherence using single-day 24-h recall data, which might not reflect long-term nutritional intake. Thus, dietary quality and adherence evaluated in our study have a possibility of classification error. To reduce the influence of error, we repeated the analysis only for those who reported that the diet on the recall day was typical. The results remained unchanged (Additional file 1: Table S1 and S2). BP measurement must also be considered. The KNHANES BP measurements were performed in the office according to a strictly predefined protocol. However, differences in office-based versus 24-h ambulatory BP measurements have been demonstrated [37]. The resulting misclassification may have affected the results in our study.

A high-quality diet was positively associated with BP control in Korean men with known hypertension. Our findings highlight the beneficial impact of dietary management as a means for achieving blood pressure control.