Diet quality and carotid atherosclerosis in intermediate cardiovascular risk individuals

The measurement of common carotid artery intima-media thickness (cIMT) allows the detection of thickening of the artery wall during the initial phases of atherosclerosis, as well as to predict the risk of its clinical complications (coronary artery disease (CAD) or cardiovascular events) [1]. Increased cIMT and/or atheromatous plaque may increase the risk of cardiovascular disease by up to four-fold in comparison with individuals who do not suffer from carotid target organ damage (cTOD) [2‐5]. To be more specific, with every increase of 0.1 mm of the cIMT, the risk of coronary heart disease is increased by 15% and the risk of cerebrovascular disease by 18% [2, 6‐9].

The cIMT has been related to several components of the Mediterranean diet (MD) in isolation (fruits, whole grain cereals, fibre, walnuts and olive oil) [10, 11]. Nevertheless, its relationship with the adherence to the MD as a whole is uncertain. Thus, some studies suggest the MD may slow down the progress of the cIMT [12, 13], whereas others do not show this association, or just show it in individuals with a basal cIMT up to 0.9 mm [14, 15]. Diet quality indices address the diet’s complexity and are calculated by a combination of foods and/or nutrients which together represent a dietary pattern [16]. The best values in these indices have been associated with positive changes in weight [17]. They have also indicated an inverse relationship with several inflammatory response markers [18]. On the other hand, the diet quality has been related with vascular health assessed by arterial stiffness and endothelial dysfunction [19]. However, there is little evidence of the association between the diet quality indices and the surrogate markers of atherosclerosis as the cIMT. For all these reasons and taking into account that the cIMT shows a greater predictive value of cardiovascular disease [20], the current study analysed the relationship between the cIMT and the diet quality. It is assessed through the Diet Quality Index (DQI) questionnaire in adults.

General, anthropometric and clinical characteristics of the participants are presented in Table 2. The age of the participants (mean ± SD) was 60.3 ± 8.4 years and 54.4% were male. Among the 500 participants, 80.2%, 27.6% and 83.6% were hypertensive, diabetics and dyslipidemics, respectively. The proportion of individuals treated with drugs was 53.2% for antihypertensives, 16.4% used antidiabetics and 37.0% with lipid lowering drugs. Systolic and diastolic blood pressure had higher values in men (p < 0.01) and heart rate was higher in women (p = 0.01). Mean values of vascular structure measurements were: cIMT (mean) 0.73 ± 0.09 mm, cIMT (maximum) 0.90 ± 0.11 mm, these are lower in women (p < 0.01). On the other hand, 83 (16.6%) subjects presented with plaque, and 85 (17.0%) had cTOD. The mean of the DQI score was 40.08 ± 2.79, with no differences observed between men and women.

In the multiple linear regression analysis, no significant association was found between DQI and cIMT (mean) in the Model 3 adjusted by age, sex and other covariables (p = 0.690) (Table 3).

The logistic regression analysis (Table 4) did not show any relation between DQI and carotid atherosclerosis. The Model 3, adjusted by age, sex and other confounders, showed no association of DQI with cIMT > 0.9 mm (p = 0.890), nor with the presence of plaques (p = 0.799) or carotid TOD (p = 0.942).

Figure 1 shows the values of the carotid mean cIMT by DQI tertiles (T1 < 39; T2 39 to 41; T3 > 41). After adjusting by age and sex and other confounders (Model 3), no association was found between DQI score and cIMT, being the differences between the DQI tertiles no significant (p = 0.458).

The results of this study show no association of the DQI with the cIMT, the presence of atherosclerotic plaques or the cTOD. These findings suggest that food quality indices may not be so useful as predictors of surrogate atherosclerosis markers as carotid damage. These results support the evidence available to date.

There is growing evidence of the relationship between cIMT with both dietary habits and individual dietary components. However, the results are inconclusive depending on whether one considers the nutritional components in isolation or consumed within a dietary pattern. The cIMT has been linked with food groups. Thus, an association between greater intake of fruit with lower cIMT has been found, especially in high cardiovascular risk individuals [11, 31, 32]. However, testing a possible association with the intake of vegetables and whole grains showed contradictory results [12, 33, 34]. Among nutrients, an inverse relationship between the ratio of poly-unsaturated to saturated fatty acid with the cIMT has been reported [35, 36]. However, the evidence is still inconsistent in relation to sodium intake, n6, n3 and other micronutrients [37]. In a similar manner, the relationship between cIMT with dietary components consumed together is unclear. Some studies have demonstrated an inverse association between dietary patterns and cIMT [12, 38, 14]. Mikkilä et al. [39], as part of the Cardiovascular Risk in Young Finns Study, determined that traditional dietary pattern (characterized by high consumption of rye, potatoes, butter, sausages, milk and coffee) was independently associated with cIMT in men. However, the health-conscious dietary pattern scores (characterized by a high consumption of vegetables, legumes and nuts, rye, tea, cheese and other dairy products) showed no significant associations with cIMT. Moreover, consumption of the Mediterranean diet, closely associated with cardiovascular health [40], has been inversely associated with cIMT though only in a population with high cardiovascular risk (cIMT >0.9 mm) [14].

The association between diet quality indices and subclinical atherosclerosis has been hardly studied. Hoebeeck et al. [41] have also studied this relationship in 2524 middle-aged adults with low cardiovascular risk of the Asklepios study and they have only demonstrated a relationship between dietary diversity score and the presence of femoral atherosclerosis, but not with the dietary quality score. Nevertheless these authors have not found any significant association, neither with cIMT nor with the presence of plaques. These findings are consistent with those obtained in our study, with a broad sample of participants with intermediate cardiovascular risk.

Some of the possible explanations why high DQI score diet failed to improve cIMT level in intermediate cardiovascular risk subjects should be addressed. It is necessary to take into account that generally nutrients are consumed in combination with others and not as isolated elements. Although the evidence points to a beneficial relation of certain nutritional components on cIMT, and therefore on subclinical atherosclerosis, this relationship is unclear when the same elements are taken with others, either in a specific food group or in the context of dietary patterns considered to be healthy. This lack of clear evidence in the relationship between c-IMT with both elements considered healthy or unhealthy could counteract the possible beneficial effect of the first by the possible detrimental effect of the latter. The short diet quality screener (SDQS), gives the highest score (3 points) to a high consumption of foods that have proven beneficial effect on cIMT [11, 31, 32] but uses the same scoring criteria for consumption of other products whose evidence is not sufficiently contrasted [12, 33, 34]. On the other hand, this relationship (cIMT-dietary habits) has been shown in individuals at high cardiovascular risk (cIMT >0.9 mm) [14]. However, it remains unclear in subjects with medium or low cardiovascular risk. The European Guidelines on Cardiovascular disease prevention in clinical practice highlights the importance in those (intermediate cardiovascular risk) subjects of promoting healthy lifestyle behaviour by tackling unhealthy lifestyles (e.g. poor-quality diet, physical inactivity, smoking) and by optimising risk factors [42, 43]. More prospective studies are therefore needed to assess this relationship in selected and more diverse populations.

The main limitation of this study is its cross-sectional design, which prevents any causal relationship between diet quality and carotid atherosclerosis being elucidated. More longitudinal studies and clinical trials are needed to explore this association. The assessment of quality index was mainly based on the DQI questionnaire, which was designed to assess the habitual diet by asking about the frequency of a limited number of food items. In spite of the fact that DQI shows a reasonable construct validity, it is important to note that it is based on the report of the habitual intake of 18 specific food items, hence some food items that may have an influence (either positive or negative) on cIMT could be not included in this questionnaire. It has also to be taken into account the role of the memory and the interpretation of the questions by the respondents.

The diet quality index is not associated with the carotid subclinical atherosclerosis in intermediate cardiovascular risk individuals.