INTRODUCTION:

Blood pressure is defined as the pressure exerted by the circulating blood upon the walls of the blood vessels. Normal range of blood pressure in adult is 120/80mm Hg⁽¹⁾. Elevated blood pressure is strongly associated with hypertension. Hypertension is multifactorial in origin⁽²⁾. Hypertension leads to various risk factors such as stroke, congestive heart failure, coronary heart disease, peripheral vascular disease, and renal failure^(3).

Dark chocolate is one of the richest source of antioxidant polyphenol⁽⁴⁾. Cocoa has a high content of plant derived flavan-3-ols. Endothelium is continuous, smooth surface of blood vessels which synthesise and release vasoactive substance⁽⁵⁾.

Studies suggest that cocoa and chocolate might protect the vascular endothelium by improving nitric oxide (NO) availability⁽⁶⁾ and decreases wave reflection which does not affect the aortic stiffness⁽⁷⁾.

As cocoa has high antioxidant property it was found to reduce the risk of cardiovascular disease⁽⁸⁾. Flavonoids may inhibit the oxidation of LDL cholesterol and reduce platelet aggregation⁽⁹⁾. Studies shows that Nitric oxide is found to improve the insulin sensitivity⁽¹⁰⁾.

This systematic review aims in evaluating the experimental and epidemiological studies associated with potential benefits of consumption of dark chocolate.

COCOA:

For centuries cocoa rich chocolate is not only recognised for its taste but also for health benefits. The main component of dark chocolate is cocoa. Cocoa is derived from cocoa bean of cocoa tree (Theobroma cacao). The major producer of cocoa is africa, while the cocoa tree is a native of central and south america. cocoa products have a rich supply of flavanoids. Cocoa has a high content of plant derived flavan-3-ols which belongs to the subclass of flavanoids containing monomer (epicatchein and catchein ) and oligomers (procyanidins) ⁽¹¹⁾. Dark chocolate has high cocoa content compared to milk chocolate.cocoa mass also contains minerals such as potassium, copper, iron, zinc and magnesium. Cocoa butter is a vegetable fat that is rich in saturated fatty acids; palmitic acid (24–27% by wt) and stearic acid (32–36% by wt) and oleic acid (33–37%)⁽¹²⁾. cocoa flavanols or procyanidins may possess immune regulatory effects and may help to modulate immune responses⁽¹³⁾.

COMPOSITION OF DARK CHOCOLATE:

Nutritional data for 100 g of dark chocolate energy value 476 kcal, total fat 25.5 g, protein 4.8g, carbohydrates 57.9g. Dry cocoa solids content in the chocolate mass 47.3%.

COCOA EFFECT ON BLOOD PRESSURE:

Brian et al conducted a cohort study in 470 elderly men free of chronic disease and estimated the cocoa intake by evaluating their dietary history for 15 years, it was found that intake of food containing cocoa is inversely associated with blood pressure⁽¹¹⁾. Davidegrassi et al conducted a crossover study related to intake of dark chocolate and white chocolate which was free of polyphenols and measured the blood pressure daily, Significantly intake of dark chocolate reduced the blood pressure^(14,6)

Dirk et al conducted a randomised controlled trial with prehypertensive patientsin which the subjects were given 6.3g of dark chocolate for 18weeks, the prevalence of hypertension was decreased from 86% to 68%⁽¹⁵⁾. A cross over study was conducted with hypertensive patients as subjects and they were given flavanol rich cocoa drink for 2 weeks, but it did not efficiently decrease the blood pressure⁽¹⁶⁾. This can be attributed due to variance in study design.

The exact mechanism behind antihypertensive effects of cocoa is not known but this may involve significant vasodilation due to increased nitric oxide (NO) bioavailability, flavanol-induced inhibition of angiotensin converting enzyme, and stearic acid-based reduction of diastolic blood pressure.

KUNA-Epidemiology of flavanoids:

McCullough et al conducted a study in which kuna indians were involved. It was found that traditional dwellers of kuna had a low blood pressure compared to people who migrated to kuna. The mortality rate due to cardiovascular disease was less. While looking through their diet it was interesting to note that their diet mainly consists of plant derived food rich in certain flavanoids⁽¹⁷⁾.

EFFECT ON LIPID PROFILE:

Obesity is associated with high lipid metabolism which leads to the risk of cardiovascular disease. Oleic acid present in cocoa butter has a positive effect on lipid levels. Short-term cocoa consumption significantly reduced blood cholesterol when given in low dose⁽¹⁸⁾. Polyphenolic compounds present in cocoa may increase the HDL concentration and suppress the LDL Oxidation ⁽¹⁹⁾. Dark chocolate consumption daily for 2 weeks and 2 hr before prolonged exercise has significant effects on the temporal response of plasma free fatty acid^(4).

EFFECT ON INSULIN SENSITIVITY:

Insulin sensitivity means small level of insulin needed to lower blood glucose leveL.

Flavanol rich dark chocolate may improve the insulin resistance therefore by improving the endothelial bioavailability of NO and decreasing the reactive formation of oxygen and nitrogen⁽²⁰⁾. The anti- oxidant effects of cocoa polyphenols directly influence insulin resistance and, in turn, reduce risk for diabetes⁽²¹⁾.

COCOA AND ITS ANTIOXIDANT PROPERTY:

Cocoa flavonoids have shown a powerful antioxidant activity providing protection against oxidation and helping prevent oxidative stress-related diseases. Antioxidant capacity of cocoa has been attributed mainly to the epicatechin content. Dark chocolate and cocoa powder may prevent cardiovascular risk by increasing serum total antioxidant capacity⁽²²⁾. Cocoa exhibits high antioxidant property when compared to tea and red wine because of high concentration of phenolic Phytochemical sand flavanoids⁽²³⁾.

ENDOTHELIAL FUNCTION:

Extract of cocoa rich in polymeric procyanidins cause an Endothelial dependant relaxation that is mediated by activation of Nitric oxide synthase⁽²³⁾. Flavonoid-rich dark chocolate improves endothelial function and is associated with an increase in plasma epicatechin concentrations in healthy adults⁽²⁴⁾. Studies show that Flavanol is the primary polyphenol responsible for cocoa induced vasodilation⁽²⁵⁾.

EFFECT ON NEURONS:

A diet rich in flavonoids such as chocolate and wine have been associated with better performance in cognitive skills in elderly people⁽²⁶⁾. Flavanol rich cocoa has been associated to increase the cerebral blood flow and found to perform cognitive tasks better in young adults⁽²⁷⁾. Contradictory, In a study conducted by david et al, it was seen that short term consumption of dark chocolate did not have much beneficial effect on neuro psychological activity^(13).

EFFECT ON PLATELET AGGREGATION:

Platelet aggregation is the critical event occurring during the initiation of coronary thrombosis, and cocoa epicatechin and catechin have been reported to modulate platelet function, by regulating glycoprotein IIa/IIIb expression⁽²⁸⁾thus reducing the risk of clot formation⁽²⁴⁾. Dark Chocolate has a dual effect on platelets. It not only decreases platelet aggregation but also reduces platelet adhesion⁽²⁹⁾

ADVERSE EFFECTS OF DARK CHOCOLATE:

Eating 50g of dark chocolate per day may reduce the risk of cardiovascular disease risk by 10.5%, but this study was based only on Short duration of dark chocolate consumption⁽³⁰⁾, the effects of long term consumption of dark chocolate is not known. Higher caloric content and prolonged use of dark chocolate may be associated with weight gain leading to obesity⁽³¹⁾. As dark chocolate containssugar, dissolution in oral cavity increases the susceptibility to dental caries.

CONCLUSION:

Dark chocolate has been known for its good taste and health related benefits such as lowering the blood pressure, insulin sensitivity, antioxidant property, maintaining blood lipid and endothelial function. These benefits are associated with high content of flavanols present in dark chocolate. But still few other questions regarding the appropriate dosage, time dependant period of dark chocolate consumption remain unanswered. Further studies must be conducted to resolve this uncertainty.

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Received on 06.05.2016 Modified on 24.05.2016

Research J. Pharm. and Tech 2016; 9(9):1505-1507.

DOI: 10.5958/0974-360X.2016.00293.6