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Published in final edited form as: Am Heart J. 2016 Oct 6;183:18–23. doi: 10.1016/j.ahj.2016.10.002

Chocolate Intake and Incidence of Heart Failure: Findings from the Cohort of Swedish Men

Daniel A Steinhaus a, Elizabeth Mostofsky b,c, Emily B Levitan d, Kirsten S Dorans b,c, Niclas Håkansson e, Alicja Wolk e, Murray A Mittleman b,c
PMCID: PMC5172457  NIHMSID: NIHMS828865  PMID: 27979037

Abstract

Aims

The objective of this study was to evaluate the association of chocolate consumption and heart failure in a large population of Swedish men.

Methods and Results

We conducted a prospective cohort study of 31,917 men 45-79 years old with no history of myocardial infarction, diabetes, or HF at baseline who were participants in the population-based Cohort of Swedish Men (COSM) study. Chocolate consumption was assessed through a self-administrated food frequency questionnaire. Participants were followed for HF hospitalization or mortality from January 1, 1998 to December 31, 2011 using record linkage to the Swedish inpatient and cause-of-death registries. During 14 years of follow up, 2,157 men were hospitalized (n = 1901) or died from incident HF (n = 256). Compared with subjects who reported no chocolate intake, the multivariable-adjusted rate ratio of HF was 0.88 (95%CI 0.78-0.99) for those consuming 1-3 servings per month, 0.83 (95%CI 0.72-0.94) for those consuming 1-2 servings per week, 0.82 (95%CI 0.68-0.99) for those consuming 3-6 servings per week, and 1.10 (95%CI 0.84-1.45) for those consuming ≥1 servings per day (P for quadratic trend= 0.001).

Conclusions

In this large prospective cohort study, there was a J-shaped relationship between chocolate consumption and HF incidence. Moderate chocolate consumption was associated with a lower rate of HF hospitalization or death, but the protective association was not observed among individuals consuming ≥1 servings per day.

Keywords: Heart failure, chocolate, epidemiology, diet

Introduction

Heart failure (HF) is a common cause of morbidity and mortality worldwide. There are an estimated 5.1 million people with HF in the United States and 23 million worldwide.1,2 Traditional contributors to the development of HF include coronary heart disease, hypertension, cigarette smoking, obesity, diabetes, and valvular heart disease. With the increasing epidemic of HF, prevention is an important public health concern.3

Recent studies indicate that chocolate products may have beneficial effects on cardiovascular health. 4-9 Importantly, multiple studies have demonstrated that consumption of chocolate reduces systolic and diastolic blood pressure after acute and chronic intake. 10-14 In addition, observational studies have shown that habitual chocolate intake is associated with lower incidence of stroke and myocardial infarction (MI),15 lower incidence of mortality from coronary heart disease,5,6 lower cardiac mortality and heart failure after incident MI,16 and improved vascular function in patients with HF. 15,17,18

There is limited research on the association of chocolate consumption and heart failure. Therefore, we studied whether chocolate intake is associated with the risk of incident HF hospitalization or mortality in a population of Swedish men.

Methods

Study Cohort

The Cohort of Swedish Men (COSM) is a population-based cohort study established in central Sweden (Västmanland and Örebro counties) and includes 48,850 men aged 45-79 years old in 1997, when baseline data were collected.19,20 The cohort includes questionnaire-based information about such modifiable lifestyle factors as diet, physical activity, smoking, weight, use of dietary supplements, some prescribed drugs, and alcohol. Cardiovascular and other diseases as well as surgeries and causes of death are identified by linkage to the National Inpatient and other registries at the Swedish Board of Health and Welfare.

We excluded subjects with an incorrect or incomplete national registration number, subjects with implausible reported energy intakes (defined as more than 3 standard deviations from the mean value of the natural logarithm-transformed energy intake), missing data for more than half of the food and beverage items, prior history of cancer, heart failure, prior myocardial infarction (MI) or diabetes, and those with missing information on chocolate consumption. We excluded men with a history of MI or diabetes at baseline because these men were more likely to have received dietary counseling that could affect their reporting of diet. After these exclusions, data on 31,917 participants were available for this analysis.

Chocolate Consumption

Diet was assessed at baseline using a self-administered 96-item, validated, food frequency questionnaire.21 For foods such as milk, coffee, cheese, and bread, which are commonly eaten in Sweden, participants reported their consumption in servings per day or per week in the past year. For chocolate and other foods, there were 8 predefined responses, ranging from never to 3+ times per day (no regular intake, 1 to 3 servings per month, 1 to 2 servings per week, 3 to 4 servings per week, 5 to 6 servings per week, 1 serving per day, 2 servings per day, and 3 or more servings per day). Participants were not asked about what type of chocolate they ate, but in the 1990s, approximately 90% of chocolate consumption in Sweden was milk chocolate, and it contained approximately 30% cocoa solids.16 A study comparing our questionnaire to 7-day diet records indicated that among Swedish men, the average portion of chocolate ranged from 26 to 42 grams.22 In contrast, the standard portion size in the United States is 28.4 grams.23

Other Covariates

We calculated total calorie intake based on the food frequency questionnaire. The questionnaire included items on education, cigarette smoking, frequency of consumption of beer, wine, and spirits, family history of MI before age 60, history of hypertension, and history of high cholesterol. History of MI at baseline was assessed through the Swedish inpatient register. We considered participants to have diabetes if they self-reported diabetes on the questionnaire or had been given any diagnosis of diabetes as recorded in the inpatient register. Physical activity was estimated by calculating metabolic equivalent in hours per day for occupational physical activity, exercise, and sedentary behavior.24 Body mass index (BMI) was calculated as weight divided by height squared (kg/m2; both self-reported).

A Dietary Approaches to Stop Hypertension (DASH) diet component score was calculated by ranking participants on intake of 1) fruits, 2) vegetables, 3) nuts and legumes, 4) low-fat dairy, 5) whole grains, 6) sodium, 7) sweetened beverages, and 8) red and processed meats.25 Participants in the highest quintile of fruits, vegetables, nuts and legumes, low-fat dairy and whole grains received a score of 5 and those in the lowest quintile received a score of 1. Participants in the highest quintile of sodium, sweetened beverages, and red and processed meats received a score of 1 and those in the lowest quintile received a score of 5. The score for each component was summed to get the overall DASH score. Participants were then categorized into quartiles based on the DASH diet component score.26

Follow-Up and Ascertainment of HF

Individuals were observed from January 1, 1998, until the date of first hospital admission or death from heart failure (HF), death from other causes, or end of follow-up (December 31, 2011), whichever came first. The primary end point was defined as a composite of hospitalization for HF as a primary or secondary diagnosis as determined through the Swedish Inpatient Registry records and the Swedish National Death Register records using the International Classification of Diseases (ICD-9) code 428 and the ICD-10 codes I50 or I11.0. The Swedish inpatient register was validated in a previous study, and 95% of the patients with these ICD codes as the primary diagnosis were confirmed to have a diagnosis of HF by medical record review, as defined by European Society of Cardiology criteria.27 Heart failure was confirmed in 82% of patients with primary or secondary diagnosis of HF.27

Statistical Analysis

Chocolate intake was categorized as no regular chocolate intake, 1 to 3 servings of chocolate per month, 1 to 2 servings per week, 3 to 6 servings per week, and ≥1 servings per day. Because some of the participants were missing data on BMI (4%) and physical activity (19%), we used Markov chain Monte Carlo multiple imputation to simulate 5 complete data sets, as previously described.19,28 All statistical analyses were performed in each data set separately. The results were averaged, and CIs and P values were calculated, accounting for the uncertainty in the imputed estimates.28

We reported baseline characteristics stratified by category of chocolate intake as mean and standard deviation or as counts with proportions, as appropriate. We used Cox proportional hazard models to compute multivariable-adjusted rate ratios with corresponding 95% confidence intervals (CIs), with participants in the lowest category of chocolate intake (none) as the reference group. For the Cox proportional hazard models, we chose covariates a priori that we considered potential confounders on the basis of their association with both chocolate intake and development of HF. In the first-stage model, we accounted for age by allowing the baseline rate to vary with age and adjusted for total energy intake (continuous). A second model was additionally adjusted for the DASH diet component score (quartile), education (less than high school, high school, university), cigarette smoking (current, past, never), alcohol consumption (never drinker, former drinker, current drinker <1 drink/week, current drinker 1-7 drinks/week, current drinker 7-14 drinks/week, current drinker >14 drinks/week), self-reported family history of MI before age 60 (yes, no), self-reported history of hypertension (yes, no), self-reported history of high cholesterol (yes, no), BMI (continuous) and physical activity (continuous). We conducted a test for the quadratic component of trend by using the median-centered value for each level of chocolate intake and determined the statistical significance of its squared value in the multivariable model.

We performed multiple sensitivity analyses. We used both primary and secondary diagnosis of heart failure in our primary analysis which has shown validity in this population;27 however, we also performed an analysis restricted to only primary heart failure diagnosis. In order to assess whether the inverse association between chocolate intake and HF was mediated through history of hypertension, the rate ratios for chocolate intake in the multivariable-adjusted model were contrasted with the estimates for chocolate intake when the indicator variable for hypertension was removed from the model. In order to further exclude patients at high risk, we performed an analysis excluding patients with hypertension and hyperlipidemia. To examine the possibility that participants reporting lower intake of chocolate had undiagnosed risk factors placing them at immediate HF risk, we conducted an analysis that excluded individuals with a follow-up time of <2 years. We evaluated the effect of healthy diet on the outcome with stratification by quartile of DASH score. We further performed an analysis stratified by smoking status for current, former, and never smokers and an analysis stratified by marital status (single, married/living with someone, divorced, widower).

Because milk consumption may inhibit the intestinal absorption of flavonoids, which may be responsible for the cardio-protective effects of chocolate,29 we calculated the product of indicator variables for chocolate intake and for milk consumption above or below the median and tested the significance of this term in the multivariable model using a likelihood ratio test. We also examined whether the association varied by regular physical activity or BMI by performing a similar test of interaction using the product of indicator variables for chocolate intake and the potential modifier.

We tested the proportional hazard assumption by including product terms of the predictors and the log of survival time, and found no significant violations. Statistical analyses were performed using SAS version 9.3. Two-sided P<0.05 was considered statistically significant.

Results

During 14 years of follow up, 2,157 men were hospitalized for first HF (n=1,901) or died of HF (n=256), corresponding to a crude rate of 5.2 cases per 1,000 person-years. Median chocolate intake was 1-3 servings per month. Compared to men reporting no chocolate intake, men who ate more chocolate had higher total daily energy intake, were more likely to be never smokers and have university-level education, and were less likely to be previously diagnosed with hypertension (Table 1).

Table 1.

Baseline Characteristics by Chocolate Intake

No Intake 1-3 Servings/mo 1-2 Servings/wk 3-6 Servings/wk ≥1 Servings/d
Characteristic (n=4209) (n=15759) (n=9005) (n=2416) (n=528)
Age, y 59.4 ± 9.2 57.8 ± 8.9 57.4 ± 8.9 59.0 ± 9.5 62.1 ± 9.9
Physical Activity, MET h/d 41.7 ± 5.1 41.7 ± 4.9 41.4 ± 4.8 41.2 ± 4.9 41.4 ± 5.1
BMI, kg/m2 25.9 ± 3.5 25.7 ± 3.2 25.5 ± 3.1 25.2 ± 3.1 25.2 ± 3.1
Energy intake, kcal/d 2529 ± 814 2664 ± 773 2874 ± 792 3034 ±811 3480 ± 1118
Alcohol consumption, g/d 17.2 ± 27.5 15.6 ± 22.9 16.0 ± 18.0 16.1 ± 16.8 19.3 ± 34.6
DASH score 24.0 ± 4.4 24.0 ± 4.1 23.7 ± 4.0 23.6 ± 4.1 23.5 ± 4.3
Cigarette smoking
    Current 1087 26.1 3688 23.7% 1974 22.2% 557 23.3% 113 21.8%
    Past 1739 41.7% 6087 39.0% 3289 37.0% 848 35.5% 181 34.9%
    Never 1344 32.2% 5818 37.3% 3637 40.9% 983 41.2% 225 43.4%
Education
    Less than high school 2913 69.8% 10432 66.5% 5432 60.6% 1443 60.2% 350 66.9%
    High school 582 13.9% 2453 15.6% 1512 16.9% 416 17.3% 64 12.2%
    University 681 16.3% 2792 17.8% 2019 22.5% 540 22.5% 109 20.8%
Family History of MI 504 12.0% 1847 11.7% 1082 12.0% 267 11.1% 54 10.2%
History of hypertension 938 22.3% 2915 18.5% 1497 16.6% 429 17.8% 91 17.2%
History of high cholesterol 534 12.7% 1895 12.0% 1021 11.3% 267 11.1% 54 10.2%
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*MET indicates metabolic equivalent of task

Missing data on physical activity (n=6150), BMI (n=1222), smoking history (n=347), education (n=179), family history of MI (n=7381)

Compared with subjects who reported no chocolate intake, the multivariable-adjusted rate ratio of HF was 0.88 (95%CI 0.78-0.99) for those consuming 1-3 servings per month, 0.83 (95%CI 0.72-0.94) for those consuming 1-2 servings per week, 0.82 (95%CI 0.68-0.99) for those consuming 3-6 servings per week, and 1.10 (95%CI 0.84-1.45) for those consuming ≥1 servings per day (P for quadratic trend= 0.001; ‘ 2).

In sensitivity analyses, the results were not materially different when we restricted the analysis to primary heart failure diagnosis or to participants with follow-up times ≥2 years. The results remained similar when we did not adjust for self-reported hypertension, and when we excluded patients with hypertension and hyperlipidemia. When stratified by quartile of DASH score, the association was similar across categories of DASH score even among those with DASH scores consistent with healthy eating patterns. Stratification by smoking status or marital status did not materially change our results. The association between chocolate intake and HF was not modified by dairy intake, BMI or physical activity. Although consumption of biscuits, pastries, candy, ice cream, and chips and popcorn was strongly related to chocolate intake, it was not associated with HF incidence.

Discussion

In this prospective study, we found that moderate habitual chocolate intake in men was associated with a lower rate of HF hospitalization or death, but the protective association was not observed with intake of ≥1 servings per day.

Chocolate has been shown to have multiple benefits to cardiovascular health, possibly mediated in part through their high concentration of plant-derived antioxidants called flavonoids. 7,30 Chocolate provides a significant dietary source of flavonoids, which are also present in tea and wine. Chocolate and cocoa flavonoids are associated with beneficial effects on endothelial function,31-35 blood pressure,7,10-14 platelets,36-39 inflammation, 40,41 high-density lipoprotein cholesterol,42 insulin sensitivity,43 and cardiometabolic makers.44 Chocolate may also have beneficial effects irrespective of flavonoid content including improved vascular function and lower leukocyte adherence capacity.9

Multiple observational studies have demonstrated that chocolate intake is associated with clinical outcomes. Chocolate intake is associated with lower incidence of stroke 22,45 and MI,15 lower incidence of mortality from coronary heart disease,5,6 and lower cardiac mortality in patients after their first MI.16

Recent prospective studies have shown that moderate chocolate consumption is associated with a lower incidence of HF in a cohort of Swedish women46 and a cohort of American male physicians.47 In the Physicians’ Health Study of 20,278 US male physicians in multivariable-adjusted hazard ratios for HF were 0.86 (0.72–1.03), 0.80 (0.66–0.98), 0.92 (0.74–1.13), and 0.82 (0.63–1.07) for chocolate consumption of <1 serving per month, 1 – 3 servings per month, 1 serving per week, 2 – 4 servings per week, and ≥5 servings per week, respectively. After stratifying by BMI, there was evidence of an inverse relationship between chocolate consumption and HF only among men with a BMI <25 kg/m2. While the distribution of BMI and the results of this study are similar to our current study, we found no modification by BMI in our population. The reason for this discrepancy is not clear but may be related to differences in the type and flavonoid content of chocolate consumed in the US compared to this Swedish cohort.

The observed J-shaped relationship between chocolate consumption and heart failure may be due to the fact that we adjusted for total daily caloric intake. Therefore, it is possible that men who consume higher levels of chocolate on a daily basis are consuming fewer calories from foods that may be salutary. Furthermore, as we were not not able to assess the exact consumption of cocoa flavonoids, it is unclear if a more linear relationship exists between flavonoids and heart failure.

There are a few limitations of our study. Because of the observational nature of the study, we cannot exclude residual or unmeasured confounding. However, we have extensive information on lifestyle, diet, and comorbid conditions and our results were robust after multivariable analyses. We also cannot exclude reverse causation, but we have attempted to limit this concern by performing a sensitivity analysis excluding the first two years of follow up.”The flavonoid content of chocolate consumed in our sample was likely relatively low; therefore our findings may underestimate the protective effects of higher-flavonoid chocolate. Alternatively, given the high percentage of milk chocolate consumption in Sweden at the time of the study, it is possible that other non-flavanoid compounds may account for our findings. However, Swedish milk chocolate has a much higher cocoa content (30%) compared to American milk chocolate which has a cocoa content of around 10%. Chocolate consumption and risk factors were measured at baseline, and there was no information on changes in chocolate consumption over time. Additionally, although the accuracy of the diagnosis of HF in the Swedish registers is high,27 they only include cases of HF that resulted in hospitalization or death, and the registers do not have information on HF etiology or type (systolic or diastolic). Despite the limitations, this study has many strengths, including a large sample size, a long duration of follow-up, and a prospective design.

In conclusion, in this population of middle-aged and elderly Swedish men, moderate habitual chocolate intake was associated with a lower rate of HF hospitalization or death, but the protective association was not observed with intake of ≥1 servings per day. Future studies are needed to determine the optimal dose of chocolate and/or cocoa flavonoids and determine the underlying mechanisms.

Table 2.

Rate Ratios and 95% CIs Comparing Different Levels of Chocolate Intake to Those Reporting No Chocolate Intake

Model 1* Model 2†
Chocolate Intake N Cases Person Years Crude Rate per 1,000 person years HR 95% CI HR 95% CI
None 4,209 371 52,633 7.05 1.00 (Ref) 1.00 (Ref)
1-3/month 15,759 1,026 204,488 5.02 0.82 0.73 0.93 0.88 0.78 0.99
1-2/week 9,005 532 117,570 4.52 0.76 0.67 0.87 0.83 0.72 0.94
3-6/week 2,416 163 30,847 5.28 0.74 0.61 0.89 0.82 0.68 0.99
≥1/day 528 65 6,417 10.13 1.01 0.77 1.32 1.10 0.84 1.45
P for quadratic trend <0.0001 0.001
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*

Cox proportional hazards model adjusted for total energy intake and accounting for age.

†

Additionally adjusted for DASH diet component score, education, BMI, physical activity, cigarette smoking, alcohol consumption, family history of myocardial infarction, self-reported history of hypertension, and self-reported history of high cholesterol

Acknowledgments

Sources of Funding

This work was supported by grants from the National Heart, Lung, and Blood Institute [grant numbers HL-120505; HL-115623; HL-007575), the European Research Council (ERC), EU 7th Research Framework Program [grant number 281760], a KL2/Catalyst Medical Research Investigator Training award (an appointed KL2 award) from Harvard Catalyst | The Harvard Clinical and Translational Science Center, National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health Award [KL2 TR001100] and the Danish Cancer Society and the Danish Council for Strategic Research (Aalborg AF-Study Group). The content is solely the responsibility of the authors and does not necessarily represent the official views of the European Research Council, Harvard Catalyst, Harvard University and its affiliated academic healthcare centers, or the National Institutes of Health. No funding organization had any role in the design and conduct of the study; collection; management, analysis and interpretation of the data; and preparation of the manuscript.

Footnotes

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Conflicts of Interest: None

Conflicts of Interest

All authors have no conflicts to declare. The authors are solely responsible for the design and conduct of this study, all study analyses and drafting and editing of the paper.

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