The Mediterranean diet is an eating model based on the dietary patterns of countries surrounding the Mediterranean Sea.1 Its key components are its high monounsaturated/saturated fat ratio and high intake of plant-based foods. Evidence indicates that this diet may be effective at lowering systolic blood pressure (SBP) and diastolic blood pressure (DBP).1-9 While some studies show that the change is insignificant,9-11 there is an overall tendency toward a beneficial effect. However, the substantial heterogeneity between the studies’ results and the modest reductions in blood pressure indicate a need for further research before substantial conclusions can be made.
A 2018 umbrella review by Dinu et al. assessed 16 medium-to-high quality meta-analyses of approximately 100 randomized controlled trials (RCTs) that investigated the Mediterranean diet’s effect on multiple health outcomes.2 Studies that compared a Mediterranean diet intervention to a control diet (typically a low-fat diet, low-carb diet, or usual American dietary habits) were included. Twenty-five of those studies found that those following a Mediterranean diet had a significant reduction in SBP of 0.67 mm Hg (95% CI [0.87 – 0.47]) and in DBP of 0.94 mm Hg (95% CI [1.55 – 0.34]). There was substantial heterogeneity between the studies’ results. It is important to note that although these reductions were statistically significant, they were small in magnitude and should be interpreted with caution with regard to clinical significance.
In a 2019 Cochrane Review,1 the authors assessed 30 RCTs on the effectiveness of the Mediterranean diet for cardiovascular disease (CVD) prevention. The reviewers selected studies with follow-up periods of at least 3 months that compared the Mediterranean diet with other dietary interventions, usual care, or no intervention for primary or secondary prevention of cardiovascular disease. To overcome some of the heterogeneity among the included studies, the authors divided their analyses into 4 sub-groups based on the type of control interventions and the measured outcomes. Two RCTs (n=269) of moderate quality comparing the Mediterranean diet to no intervention over 3 to 24 months showed a mean reduction in SBP of 2.99 mm Hg (95% CI [3.45 – 2.53]) and in DBP of 2.00 mm Hg (95% CI [2.29 – 1.71]). The authors did not comment on any relationship between weight loss and the drop in blood pressure.
The effects of the diet may be long-term. A parallel-arm RCT by Doménech et al. studied the one-year effect of the Mediterranean diet supplemented with either extra virgin olive oil (MedDiet + EVOO) or nuts (MedDiet + Nuts).3 The authors followed 235 people with high cardiovascular risk who were randomized from the PREDIMED study to either the MedDiet + EVOO group, MedDiet + Nuts group, or a low-fat control group. At baseline, 85.4% had hypertension. After adjustment, authors found significant decreases for the MedDiet + EVOO group in mean SBP of 2.3 mm Hg (95% CI [-4.0 – -0.5]) and in mean DBP of 1.2 mm Hg (95% CI [-2.2 – -0.2]) compared to baseline. Similarly, they found significant decreases for the MedDiet + Nuts group in mean SBP of 2.6 mm Hg (95% CI [-4.3 – -0.9]) and mean DBP of 1.2 mm Hg (95% CI [-2.2 – -0.2]). These reductions in 24-hour ambulatory blood pressure were significantly greater for the MedDiet groups than the control group for both SBP (p=0.001) and DBP (p=0.017). There was no significant weight loss in any arm and no between-group differences in weight loss.
Other studies showed mixed results with regard to the significance of the reduction.9,10 A systematic review and meta-analysis by Nissensohn et al. analyzed six RCTs (n>7,000) that compared a Mediterranean diet to a low-fat diet.10 They included studies in which the diet was followed for at least one year and participants had normal blood pressure or mild hypertension. Compared to a low-fat diet, the Mediterranean diet led to a non-significant decrease in SBP of 1.44 mm Hg (95% CI [-2.88 – 0.01]) and a modestly significant decrease in DBP of 0.70 mm Hg (95% CI [-1.34 – -0.07]). The authors concluded that there was a positive and significant association between the Mediterranean diet and blood pressure, but the effect was small in magnitude. They further stated that the results should be interpreted with caution due to the small number of studies and substantial heterogeneity.
Kastorini et al. conducted a meta-analysis of 50 studies (n=534,906) that examined the effect of the Mediterranean diet on metabolic syndrome and its components.9 Of the 50 studies, 14 clinical trials (n=3060) measured the effect of the Mediterranean diet on blood pressure. These trials compared the Mediterranean diet to a control diet that was either a low-fat diet, usual diet, or high saturated fat diet. Of the fourteen clinical trials evaluating blood pressure, three found a significant reduction in blood pressure among those on a Mediterranean diet compared to the control diet. SBP dropped by a mean of 2.35 mm Hg (95% CI [3.51 – 1.18]) and DBP dropped by a mean of 1.58 mm Hg (95% CI [-2.02 – 1.13]). In the other eleven studies, the systolic blood pressure of people who adhered to the Mediterranean diet was either elevated slightly or not significantly lower compared to those on the control diets. Among six cross-sectional studies, there was no significant association between adherence to the Mediterranean diet and blood pressure. The authors noted that significant heterogeneity was found in the analysis of the studies, limiting the generalizability of these results.
Overall, although studies of the Mediterranean diet’s effect on blood pressure produce results with noticeable variation, they tend toward a beneficial effect.
References
- Rees K, Takeda A, Martin N, et al. Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev. 2019;3:Cd009825.
- Dinu M, Pagliai G, Casini A, Sofi F. Mediterranean diet and multiple health outcomes: an umbrella review of meta-analyses of observational studies and randomised trials. Eur J Clin Nutr. 2018;72(1):30-43.
- Domenech M, Roman P, Lapetra J, et al. Mediterranean diet reduces 24-hour ambulatory blood pressure, blood glucose, and lipids: one-year randomized, clinical trial. Hypertension. 2014;64(1):69-76.
- Davis CR, Hodgson JM, Woodman R, Bryan J, Wilson C, Murphy KJ. A Mediterranean diet lowers blood pressure and improves endothelial function: results from the MedLey randomized intervention trial. Am J Clin Nutr. 2017;105(6):1305-1313.
- Ndanuko RN, Tapsell LC, Charlton KE, Neale EP, Batterham MJ. Dietary patterns and blood pressure in adults: a systematic review and meta-analysis of randomized controlled trials. Adv Nutr. 2016;7(1):76-89.
- Schwingshackl L, Chaimani A, Hoffmann G, Schwedhelm C, Boeing H. A network meta-analysis on the comparative efficacy of different dietary approaches on glycaemic control in patients with type 2 diabetes mellitus. Eur J Epidemiol. 2018;33(2):157-170.
- Godos J, Zappala G, Bernardini S, Giambini I, Bes-Rastrollo M, Martinez-Gonzalez M. Adherence to the Mediterranean diet is inversely associated with metabolic syndrome occurrence: a meta-analysis of observational studies. Int J Food Sci Nutr. 2017;68(2):138-148.
- Garcia M, Bihuniak JD, Shook J, Kenny A, Kerstetter J, Huedo-Medina TB. The effect of the traditional Mediterranean-style diet on metabolic risk factors: a meta-analysis. Nutrients. 2016;8(3):168.
- Kastorini CM, Milionis HJ, Esposito K, Giugliano D, Goudevenos JA, Panagiotakos DB. The effect of Mediterranean diet on metabolic syndrome and its components: a meta-analysis of 50 studies and 534,906 individuals. J Am Coll Cardiol. 2011;57(11):1299-1313.
- Nissensohn M, Roman-Vinas B, Sanchez-Villegas A, Piscopo S, Serra-Majem L. The effect of the Mediterranean diet on hypertension: a systematic review and meta-Analysis. J Nutr Educ Behav. 2016;48(1):42-53.e41.
- Gay HC, Rao SG, Vaccarino V, Ali MK. Effects of different dietary interventions on blood pressure: systematic review and meta-analysis of randomized controlled trials. Hypertension. 2016;67(4):733-739.
