In this prospective study, we found that 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 three or more servings per week. Results were similar when we did not adjust for self-reported hypertension and when we restricted the analysis to subjects with follow-up times greater than 2 years. Furthermore, consumption of snacks were all strongly related to chocolate intake but was not associated with HF, suggesting a specific association between chocolate and HF incidence.
Chocolate is one of the most concentrated sources of flavanoids,23
a subclass of polyphenols. Short-term randomized feeding trials suggest that the flavanoids in chocolate may be responsible for the improvement in cardiovascular risk factors3, 4
. Some5, 6, 24
but not all25,26
feeding trials have indicated that chocolate intake significantly reduced systolic and diastolic blood pressure, possibly by acting as an angiotensin I converting enzyme inhibitor27, 28
. Flavanoids may protect against LDL oxidation8, 29, 30
through increased antioxidant capacity and diminished production of oxidative products in plasma7
. The increased production of nitric oxide also causes increased vasodilation and inhibits platelet aggregation8
. Cocoa and chocolate intake is associated with lower platelet activation after a single dose31–34
, improved endothelial function35–38
, increased HDL39
and reduced inflammation40, 41
. Dark chocolate has also been shown to influence metabolic function. Daily intake of 100 g of dark chocolate for 2 weeks reduced fasting insulin and glucose levels and decreased glucose and insulin responses after an oral glucose load42, 43
Although the association between chocolate intake and HF is not known, there have been observational studies documenting its association with lower blood pressure9, 10
, lower incidence of stroke and myocardial infarction (MI)9, 10
, lower incidence of mortality from coronary heart disease (CHD)4, 11
and lower cardiac mortality in patients surviving their first MI12
. Furthermore, a recent meta-analysis reported that flavanoid intake is associated with decreased cardiovascular mortality4
There are several aspects of this study that warrant discussion. Although we had extensive data on lifestyle, diet and comorbid conditions, we cannot rule out residual or unmeasured confounding. However, our results are robust after using multivariable analyses that adjust for age, socioeconomic status, smoking status and other potential confounders17
. Our food-frequency questionnaire was validated in a study comparing four 7-day open-ended diet records to the food-frequency questionnaire15
and indicates that the reporting of intake of sweets was well reported (spearman correlation=0.6). Furthermore, if the misclassification of chocolate was unrelated to HF incidence, the results would likely be an underestimate of the protective effect of chocolate. Chocolate consumption and risk factors were only measured at baseline so we have no information on how changes in chocolate consumption may have impacted a participant's risk of incident heart failure.
In the European Union, dark chocolate must consist of at least 35% cocoa solids and in the United States, the minimum is set at 15%12
. Despite the fact that most of the chocolate consumed in our sample probably contained relatively low concentrations of the potentially protective ingredients (approximately 30% cocoa solids12
), we still saw a statistically significant trend, suggesting that our findings may underestimate the protective effects of dark chocolate.
Our observed incidence rate of heart failure of 15.1 cases per 10,000 woman-years is similar to the reported incidence rate among women in the national Swedish registers discharged in 2000 (17.1 cases per 10,000 woman-years)44
. Although the accuracy of the diagnosis of HF in the Swedish registers was shown to be high20
, only cases of HF that resulted in hospitalization or death were recorded. In addition, the registers do not contain information on HF etiology or subtype (systolic vs. diastolic). Our assessment of hypertension and high cholesterol was based on self-report, which is inherently less reliable than clinical measurement. On the other hand, this study has many strengths, including a large sample size and long duration of follow-up and the prospective nature of our study reduces the potential for bias caused by differential recall of chocolate intake by cases and non-cases of HF.
In conclusion, in this population of middle-aged and elderly Swedish women, 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 one or more servings per day. Further studies are needed to confirm or refute these findings and to determine the optimal dose and type of chocolate and to clarify the mechanisms involved.