Healthy eating index 2015 and major dietary patterns in relation to incident hypertension; a prospective cohort study

Hypertension (HTN) is a global health problem, the principal cause of cardiovascular diseases (CVDs) and premature death, affecting roughly one billion adults worldwide [1, 2]. By 2030, it is estimated that 41% of American adults will have been diagnosed with HTN [3]. In contrast to the trends reported in the USA and northern Europe, evidence indicates that CVDs mortality is rising in Iran, and 24% of females and 22% of males suffer from HTN [4, 2]. HTN is a multifactorial disease caused by a complex combination of dietary, lifestyle, and genetic risk factors [5]. The high prevalence of HTN can be attributed to sedentary behaviour, obesity, smoking, family history, and an unwholesome diet [2, 5, 6]. Interestingly, not only is it a curable and well-modifiable disease the controlled HTN but also improves the life quality and the prognosis and prevents relating clinical complications [2, 7]. The main approaches for preventing and managing HTN are lifestyle changes, involving physical activity, weight loss, and dietary modifications [2, 8, 9].

Dietary modifications play a crucial role in preventing and managing HTN[1]. Numerous studies have been conducted over the past few decades that highlight the importance of dietary modification in developing and controlling HTN [8‐11]. Several indices have recently been developed to examine the healthiness of dietary patterns. Due to the interaction of nutrients in foods, it is often impossible to differentiate the effects of specific dietary ingredients. Accordingly, the usage of these indices and dietary patterns has evolved to assess the effects of overall dietary intake [10, 12, 13]. There is also the “food group effect”. Food intake is multidimensional exposure, namely food and component effect, contaminants, additives. Assessment of dietary patterns increases the ability to assess more substantial effects due to the cumulative effects of many diet factors (inter-correlations), and allow assessing of the interaction among synergistic components. Since 1995 the healthy eating index (HEI) has been a dietary index developed to evaluate the diet's quality in accordance with Dietary Guidelines for Americans (DGA). The HEI is updated every five years by the evidence-based recommendations of the United States Department of Agriculture (USDA) and Health and Human Services (HHS) [14, 15]. The latest version of this index is the HEI 2015 index noting two essential features in nutrition guidelines, adequacy moderation for dietary intakes. The first part consists of 9 food items, including total fruits, whole fruits, total vegetables, greens and beans, whole grains, dairy, total protein foods, seafood and plant proteins, and fatty acids and the second part that means limitation intake is related to following four food items, refined grains, sodium, added sugars, and saturated fats [14, 16].

Despite the tremendous increase in the prevalence of HTN in Iran [17], there are no standard quantitative dietary guidelines to evaluate dietary patterns and their relationships with HTN [5]. Additionally, little information about the relation between HTN and HEI 2015 and major dietary patterns in the Kurdish population is known. The Ravansar Non-Communicable Disease cohort study [18] provided this opportunity to estimate dietary patterns and HTN associations from an epidemiological standpoint. Therefore, the current study investigated the HEI 2015 and major dietary patterns in relation to incident HTN.

The mean age was 46.5 ± 7.89 years and 48.83% were male. The representative random sub-cohort of 1295 participants was selected for this case-cohort study in the current prospective study. After exclusions, 294 incidents of HTN occurred. The mean weight, BMI, and WC in cases were significantly higher than in the sub-cohort group. In addition, the mean PA of cases was remarkably lower than in the sub-cohort group (P < 0.001). There was no significant difference between two studied groups regarding gender (P < 0.001). Baseline characteristics of the study population in both studied groups are shown in Table 3.

The food groups intake results determined three major dietary patterns: plant-based, high protein, and unhealthy. The plant- based diet was characterized by higher adherence to leafy vegetables, starchy vegetables, carotene-rich vegetables, tomato, potato, legumes, nuts, olive, vegetable oil, fresh and dried fruits, and fruit juice. Another major dietary pattern, a high protein diet, tended to a higher intake of red and white meat, legumes, egg, whole, and refined grains. In addition, unhealthy dietary pattern was specified with a higher factor loading of salt, sweet, dessert, butter, hydrogenated fat, soft drink, refined grain, tea, and coffee. (Table 4).

Table 5 shows the correlation between HEI 2015 and the major identified dietary patterns. According to it, there was a significant positive correlation between HEI 2015 with plant-based (r = 0.492) and high protein (r = 0.255) diets, while there was a notable inverse correlation between HEI 2015 and unhealthy diet (r = -0.473).

This present study revealed that the individuals in the highest quartile of HEI-2015 had a 39% lower risk of incident HTN than the participants in the first quartile (Model I: HR: 0.61; 95% CI: 0.46–0.82). After adjustment for potential confounders, including age, gender, SES, education, physical activity, diabetes, BMI, and energy intake, this association was remained (Model IV: HR: 0.7; 95% CI: 0.51–0.97). (Table 6) (Fig. 1, A) Similarly, among the major identified dietary patterns, persons who were the highest tertile of the plant-based dietary pattern were at lower risk of incident HTN in both crude and adjusted models (Model I: HR: 0.69; 95% CI: 0.54–0.9) and (Model IV: HR: 0.7; 95% CI: 0.53–0.94), respectively. (Table 6) (Fig. 1, B) However, the other two identified dietary patterns were not associated with incident HTN. (Table 6) (Fig. 1, C and D).

Likewise, we observed that among the HEI- 2015 components, the participant who had higher scores of total fruits, fatty acids, and sodium were at lower risk of HTN incident (HR: 0.93; 95% CI: 0.85–0.99), (HR: 0.96; 95% CI: 0.92–0.99), and (HR: 0.96; 95% CI: 0.92–0.99), respectively. Other the HEI- 2015 components had no significant association with HTN incidents. (Table 7).

This large prospective Kurdish population-based study extracted three major dietary patterns using principal component analyses methods, including plant-based, high protein, and unhealthy dietary patterns. We found that greater adherence to HEI 2015 and the plant-based dietary pattern has inversely correlated with the risk of incident HTN. Moreover, among the HEI- 2015 components, a higher score of total fruits, fatty acids, and sodium was associated with a reduced risk of incident HTN. There was no significant association between the other two identified dietary patterns (high protein and unhealthy dietary patterns) and incident HTN.

HTN contributes as one of the most critical risk factors for CVDs and their mortality estimated 874 million adults had an SBP of more than 140 mm Hg or higher in 2015 [21]. Diet modification is an effective strategy to prevent it [22]. Understanding national dietary patterns and their relationship to the risk of chronic non-communicable diseases overcomes the challenge of examining individual foods or nutrients and considering their common effects [23]. In this regard, limited data are available from Kurdish dietary patterns, and to the best of our knowledge, the major dietary patterns were identified and were compared to HEI 2015. The association between them and incident HTN was also evaluated.

This study indicated that higher adherence to HEI 2015 had a preventive effect on incident HTN. Similarly, greater adherence to the plant-based pattern that emphasized the higher intake of vegetables, especially leafy vegetables, fresh fruits, legumes, and whole grains, decreased incident HTN; the high protein diet, however, had no association with incident HTN. According to other studies, high protein diets are associated with higher blood pressure. Therefore, people with high protein diets may have higher blood pressure [1, 6, 24]. A systematic review and meta-analysis of 15 prospective cohort studies showed that higher diet quality characterized by HEI 2005, 2010, and the alternate healthy eating index (AHEI) was significantly related to decreasing all causes of mortality, including CVDs, cancer, and type 2 diabetes [25]. In three populated prospective cohort investigations, greater adherence to various wholesome eating patterns was consistently associated with lower cardiovascular disease risk [26]. A cross-sectional analysis of the Fasa PERSIAN study suggested that the HEI-2015 diet may prevent hypertension [2]. On the contrary, in our study Tehran Lipid and Glucose Study Increasing DASH score, the healthy and unhealthy dietary patterns were not associated with the risk of hypertension [5]. Hu et al. presented that greater following HEI 2015 was significantly lessened CVDs incidence (HR: 0.84; 95% CI: 0.76–0.93) and CVDs mortality (HR: 0.68; 95% CI: 0.58–0.8) [27]. However, HTN was not assessed in these studies. Another systematic review and meta-analysis of 15 randomized clinical trials demonstrated that the vegetarian diet lowered both systolic and diastolic blood pressure compared to the omnivorous diet [28]. A case-cohort study after 1.61 years follow up of 686 vegetarians showed that they were 34% less likely to develop HTN than people who did not follow a vegetarian diet (Odds Ratio(OR): 0.66; 95% CI: 0.5–0.87) [29]. A study by Song et al. showed that women who consumed higher legumes and whole-grain were lower at risk of HTN incidence (HR: 0.77; 95% CI: 0.59–1) [30]. In contrast, the results of Thai cohort study displayed that dietary pattern characterized by greater adherence to vegetables, fruits, soybean products, and milk was not associated with HTN (OR: 0.99; 95% CI: 0.86–1.15) [22]. Likewise, in the Mexican Teachers’ cohort study, there was no significant association between dietary patterns tended to vegetable, fruits, and legumes and HTN (OR: 0.94; 95% CI: 0.84,-1.05) [23].

Plant-based diets are generally higher in terms of diet quality than non-plant-based diets due to their high content of fiber, antioxidants, potassium, and low saturated fat and sodium [31‐33]. A plant-based diet prevents incident HTN with beneficial effects on blood viscosity, vasodilation and reduced insulin resistance [28, 34]. Also, with its antioxidant and anti-inflammatory properties and the content of valuable fibres, it changes the colony and strains of the intestinal microflora and improves blood pressure by influencing the renin-angiotensin system and baroreceptors [33, 35]. According to the Lea Borgi study, consuming whole fruits for a more extended period and increasing consumption may reduce the risk of hypertension [36]. In A study conducted in Bangladesh, additionally, found that a higher intake of fruits and vegetables was associated with lower annual pulse pressure and systolic blood pressure, while a higher intake of meat was correlated with higher annual pulse pressure [37]. Based on a systematic review and network meta-analysis, the DASH diet may be the most effective dietary measure for lowering blood pressure between hypertensive and pre-hypertensive patients based on high-quality studies [1]. Hence, researchers have referred to it as the dietary approach to stop hypertension (DASH). To prevent hypertension, it emphasizes limiting sodium intake and increasing potassium intake through vegetables and fruits consumption [38, 39]. A systematic review and meta-analysis on 30 randomized clinical trials observed that adherence to the DASH diet can significantly lower blood pressure in hypertensive and healthy adults [40]. Francisco et al., in their study, reported that adherence to the DASH diet was associated with a significant reduction in blood pressure, even with a short follow-up period [41]. Legumes, fruits and vegetables are enriched antioxidants and essential vitamins, including fibre, vitamin C, potassium, folic acid, magnesium, flavonoids, and carotenoids, and have synergistic effects on lowering blood pressure by improving endothelial function and their antioxidative properties causing vasodilation [42, 43].

Our findings from the HEI 2015 showed that greater score of total fruits, fatty acids, and sodium was associated with a lower risk of incident HTN. In other words, limiting the intake of sodium and adequately unsaturated fatty acids compared to saturated fatty acids and sufficient fruits consumption, reduces the development of HTN. Moreover, in this study, higher adherence to an unhealthy diet was inversely related to HEI 2015 and raised the risk of incident HTN, although this association was insignificant even with controlling potential confounder variables. The study by Mendonça et al. on Spanish adults reported that higher adherence to diet with high content of saturated fats and salt and low content of fresh vegetables and fruits as ultra-processed foods was significantly increased the risk of incident HTN (HR: 1.21; 95% CI: 1.06- 1.37) [44]. The modern diet is associated with processed foods, also known as the Western diet. This pattern is associated with increased intake of calories, sodium, saturated fats, and decreased potassium [45, 46]. High sodium intake is the leading cause of increased hypertension, which inhibits the sodium pump and stimulates the sodium-calcium exchanger type 1 (NCX1), resulting in increased intracellular calcium concentration, which causes vasoconstriction [47, 48]. Additionally, high sodium intake reduces the synthesis of nitric oxide (NO) and increases the plasma level of the endogenous NO inhibitor, which reduces vasodilation [49, 50]. On the other hand, reducing potassium intake and affecting the sodium pump inhibit potassium channels in the cell membrane and increase intracellular calcium, which eventually leads to HTN[51, 52]. All of these factors contribute to the development of HTN [48].

The other two features of HEI 2015 had preventive effects of incident HTN were total fruits and fatty acids. Adequate intake of fruits along with high content of antioxidants, vitamins, minerals and fiber as nutritious diet items play a role in weight control and anthropometric indicators and reduce systemic blood pressure [42, 53]. Unsaturated fatty acids, especially omega-3 fatty acids, play an essential role in vascular vasodilation by increasing the bioavailability of NO and having anti-inflammatory effects [54].

To conclude, our findings supported the association between the HEI 2015 and incident HTN. Among the major identified dietary patterns, plant-based and high protein diets were positively correlated with HEI 2015, while the unhealthy diet was inversely correlated with HEI 2015. Similarly, the plant-based diet, and greater score of total fruits, fatty acids, and sodium were preventively associated with incident HTN. Furthermore, the other two dietary patterns had no significant association with incident HTN. Therefore, according to the HEI 2015 recommendations, our study recommends limiting sodium intake and adequate vegetables and fruits consumption.