By Rebecca L. Fahey, MD, PhD, MBA

Integrative Medicine Epidemiologist, Wheeling, WV

Dr. Fahey reports no financial relationships relevant to this field of study.

SYNOPSIS: A prospective cohort study and confirmatory meta-analysis on Swedish adults determined chocolate consumption is associated with lower risk of myocardial infarction and coronary artery disease.

SOURCE: Larsson SC, Akesson A, Gigante B, Wolk A. Chocolate consumption and risk of myocardial infarction: A prospective study and meta-analysis. Heart 2016;102:1017-1022.

SUMMARY POINT

  • Mounting evidence in the literature indicates that high consumption of chocolate is associated with a 10% lower risk of myocardial infarction and coronary artery disease.

We are observing a trend in the medical literature on food as medicine. For instance, chocolate and cocoa flavanol consumption have demonstrated improvements in the cardiovascular health of adults.1-6 Increasing evidence from randomized, controlled trials suggests favorable effects of cocoa on insulin sensitivity, high-density lipoprotein levels, blood pressure, and endothelial function. In addition, several prospective studies and meta-analyses have confirmed and expanded on these data. For example, the incidence of myocardial infarction (MI) was studied in relationship to chocolate consumption to clarify the assumption that chocolate has an inverse effect on coronary artery disease (CAD).

Larsson et al performed a prospective study and a confirming meta-analysis to identify patterns of MI risk among study participants. Data from two prospective cohorts, the Cohort of Swedish Men and the Swedish Mammography Cohort, included 67,640 participants after exclusions (36,535 men and 31,105 women) between 45-83 years of age. The authors used a food frequency questionnaire (FFQ) applied in 1997 as a baseline. Participants were placed into four of the eight groups based on their chocolate consumption. Covariates and demographics of the participants were obtained from a self-administered questionnaire, the Swedish National Diabetes Register, and the Swedish National Patient Register. MI case ascertainment was determined from the Swedish National Patient Register, the Swedish Cause of Death Register, and the National Board of Health and Welfare.

Statistical analysis for all participants was based on the time range from Jan. 1, 1998, until one of three dates was confirmed: date of diagnosis of MI, date of death, or Dec. 31, 2010. Hazard ratios (HR) for covariates were established using the Cox proportional hazards regression model and established as relative risks (RR) with 95% confidence interval (CI) of MI, according to categories of chocolate consumption. The following four groups were used for chocolate consumption: never, 1-3 times/month, 1-2 times/week, and 3-4 times/week. Two multivariate models were established to categorize the covariates, and the first model was formed into groups by age and sex. The first multivariate model included the following covariates: education, family history of MI before age 60, smoking, aspirin use, walking/bicycling, exercise, total energy intake, processed meat, fruits, and vegetables. The second multivariate model included the above covariates plus body mass index (BMI), history and diagnosis of diabetes, hypertension, and hypercholesterolemia at baseline. The HR was established as satisfactory using Schoenfeld residuals.

Within the Cox model, a continuous variable for the median value of chocolate consumption within groups was established to determine linear trends. This variable was used to examine the association between MI risk and chocolate consumption and was modified by sex, education, and a history of diabetes, hypertension, and hypercholesterolemia at baseline. The likelihood ratio test was used to verify the statistical significance of effect.

A meta-analysis was performed combining the results of the Swedish study with previous prospective studies on chocolate consumption and MI or CAD risk. An established level of chocolate consumption was assumed to be 30 grams.

The Swedish study, which lasted a mean of 13 years with 67,640 participants found 4,417 cases with 897 deaths from MI. Interestingly, those individuals who consumed the most chocolate ( 3-4 servings/week) were more likely to have a college education, have higher total energy intake, and eat more processed meat, and were less likely to smoke, be overweight, and have a history of diabetes, hypertension, and hypercholesterolemia. The study found that chocolate consumption was associated with a lower MI risk even with the covariates mentioned above. In the first multivariate model, men and women who consumed the most chocolate ( 3-4 servings/week) had a 20% (95% CI, 10-30%; P < 0.002) lower risk of MI than non-consumers of chocolate. In the second multivariate group that was adjusted for BMI and a history of diabetes, hypertension, and hypercholesterolemia at baseline, the reduction in MI risk was 13% (95% CI, 2-23%; P < 0.04).

The results of the five prospective studies and the Swedish study selected for the meta-analysis found 6,851 CAD cases from 144,823 adult participants. The data from these prospective studies came from five different countries (Sweden, Germany, United Kingdom, United States, and Australia). When results from all six studies were joined, the overall RR for the highest vs. lowest category of chocolate consumption was 0.90 (95% CI, 0.82-0.97), with little heterogeneity (I2 = 24.3%) between studies. The dose-response meta-analysis overall RR per 50 g/week of chocolate consumption was 0.95 (95% CI, 0.92-0.98) without heterogeneity between studies (I2 = 0%). Two of the six studies identified the type of chocolate consumed: chocolate bars, plain chocolate, chocolate snack bars, and plain cocoa for drinks.

COMMENTARY

Increasing evidence from randomized, controlled trials and prospective cohort studies emphasizes the benefits of regular chocolate consumption.1-8 Participants consumed different types of chocolate during the studies, and the authors did not distinguish between dark and milk chocolate. A lower risk of MI and CAD is assumed to be stronger for dark chocolate, which has higher cocoa content than milk chocolate. Further studies are needed to clarify the amount and types of chocolate. Chocolate has been proven to affect insulin sensitivity, vascular endothelial function, and activation of nitric oxide, and has been shown to decrease oxidation, blood pressure, inflammation, plaque formation in the vasculature, and formation of blood clots.6,9,10 Its beneficial properties come from the polyphenols and flavonoids (flavan-3-ol, epicatechin).11 Polyphenols are abundant micronutrients found in plants that have antioxidant properties. Flavonoids are a specific polyphenol found in chocolate, vegetables, fruits, legumes, red wine, and green tea.9,11

Overall, there is a strong association between chocolate consumption and decreased risk for cardiovascular disease.1-6 Along with a healthy diet, the consumption of high (> 70%) cocoa solid (flavanol)-containing chocolate bars is recommended to decrease a 10-year risk of cardiovascular disease.3 Causality has been established between intake of flavanols and improved endothelial function.12 More research is recommended on the benefits of milk vs. dark chocolate and the dose-response relationship and the effects on cardiovascular disease risk.

One major limitation of this study was that the FFQ had only one question on chocolate consumption. Not all health benefits of chocolate are created equally: The darker the chocolate, the more cocoa solid it contains and the more flavanol. Although, studies have suggested that (> 70%) cocoa solids have the most overall benefits, it is hard to know actually how much cocoa solid or flavanol is available in the chocolate after processing.13

The overall recommendation is to increase consumption of plants containing polyphenols (flavanol) because of the antioxidant capabilities. Increased consumption should include chocolate, vegetables, fruits, legumes, red wine, and green tea.11 Those who consumed 30 grams (the average bar consumed by Swiss men) of chocolate ( 3-4 servings/week) decreased the risk of CAD the most. Consuming dark chocolate (> 70% cocoa solids) would increase the amount of flavanols in the diet.

REFERENCES

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  2. Mastroiacovo D, Kwik-Uribe C, Grassi D, et al. Cocoa flavanol consumption improves cognitive function, blood pressure control, and metabolic profile in elderly subjects: The Cocoa Cognition, and Aging (CoCoA) Study — a randomized controlled trial. Am J Clin Nutr 2015;101:538-548.
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