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A chocolate bar a day keeps the cardiologist away

Chocolate is good for you? What is this, Sleeper? Strangely enough, this addictive treat, loaded with fat and sugar, does seem to be showing consistent, positive effects on cardiovascular health.

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Chocolate is made with cocoa, which is processed from the seeds of a cacao tree (cocoa beans). Cacao has been cultivated for at least 3 millennia in Mesoamerica. Western Africa produces most of the cocoa today, 40% from Ivory Coast. Once the cacao seeds are fermented, dried, and roasted, the hulls are removed, and the remaining cocoa liquor is pressed to separate the cocoa butter from the solids, which are ground to form cocoa powder.

Cocoa has been studied for its many effects on the human body, with particular interest in cardiovascular and cognitive effects. In the cardiovascular arena, cocoa may have antihypertensive, anti-inflammatory, anti-atherogenic, and anti-thrombotic effects. These effects are thought to be due to flavonoids, a group of polyphenolic compounds found ubiquitously in plants. High amounts are found in parsley, onions, berries, teas, bananas, citrus fruits, Ginkgo biloba, red wine, and dark chocolate. Flavonoids are antioxidants that may suppress oxidation of low-density lipoproteins and may reduce risk of cardiovascular disease including stroke. They have also demonstrated anti-allergic, antimicrobial, anti-cancer, and anti-diarrheal activities in vitro.

In cocoa, the flavonoid subcategory thought to be responsible for the antioxidant activity is flavanols, specifically the monomer catechin and its stereoisomer epicatechin. Despite the fact that most of these compounds are destroyed in cocoa processing, chocolate still contains a substantial amount at 460 to 610 mg/kg. Green and black teas and beans can also be quite high in flavanols. Red wine, and fruits such as apricots, cherries, grapes, blackberries, peaches, and apples are additional good sources.

The first inkling that cocoa might have health benefits came from the Kuna people who live on the San Blas islands in Panama. Every day they consume large quantities of a cocoa beverage made from locally grown cacao. An observational study showed that deaths due to cardiovascular causes, cancer, and diabetes mellitus occurred much less frequently in the Kuna compared with people living on the mainland. Cardiovascular events leading to mortality were considerably fewer (8.28 vs. 119 per 100,000). Cancer events were also fewer (3.68 vs. 74.7 per 10,000), as were deaths due to diabetes mellitus (3.68 vs. 24.4 per 10,000). The data were consistent annually over a 4-year period for ischemic heart disease, cancer, stroke, and diabetes. These 2 populations differ in many aspects, not just cocoa consumption, so the actual cause(s) of the differences reported could not be confirmed.

In 2011, a meta-analysis summarized data across 7 observational studies involving 114,009 participants, looking at cardiometabolic disorders including cardiovascular disease (coronary heart disease [CHD] and stroke) and chocolate consumption. When data were compared from subjects with the highest vs. lowest level of chocolate consumption, in 5 of the 7 studies, a significant reduction was seen in the risk of developing cardiometabolic disorders with higher chocolate intake. This difference was noted even after adjustment for potential confounders (eg, age, physical activity, body mass index (BMI), smoking status, dietary factors, education, and drug use). The authors conclude that these favorable effects seem mainly mediated by the high polyphenol content in cocoa products and probably accrue by increasing the bioavailability of nitric oxide, which subsequently might lead to improvements in endothelial function, reductions in platelet function, and additional beneficial effects on blood pressure (BP), insulin resistance, and blood lipids.

Two other large observational studies provided similar results: In the Swedish mammography cohort (N=33,372, ages 49-83, with no history of cancer, stroke, CHD, or diabetes mellitus), a 20% lower risk of stroke within 10 years was reported in women who ate more than 45 g of chocolate (1.6 oz) each week compared with those who ate less than 9 g (0.3 oz) a week (Cox proportional-hazards model). And in the European Prospective Investigation into Cancer (EPIC)-Norfolk cohort (N=>20,000), in the 11-year follow-up period, CHD was reported in 9.7% and 13.8% in the highest and lowest chocolate consumption quintiles, respectively, and stroke was reported in 3.1% and 5.4%, respectively. Multivariate-adjusted hazards ratios showed a 12% difference for CHD and a 9% difference for cardiovascular disease (CHD or stroke) between the 2 groups.

The effects of chocolate consumption on specific markers of cardiovascular health have been examined in small, controlled studies. Here are some examples:

Improvements in endothelial function associated with chocolate consumption were reported in 2 small, randomized, controlled studies (N=30 and 21). Young healthy subjects who consumed 8 g of chocolate containing 70% cocoa daily for 1 month demonstrated significantly higher flow-mediated dilation (FMD) values compared both with controls and with their own baseline values. No significant changes in body weight, BMI, heart rate, BP, or blood sugar were seen in either group. In a similar study conducted at UCSF, healthy adults consumed either high- or low-flavanoid dark chocolate daily for 2 weeks. The high-flavanoid chocolate contained 213 mg procyanidins and 46 mg epicatechin. After 2 weeks, mean FMD values had increased by 1.3 ± 0.7% from baseline in the high-flavanoid group but decreased 0.96 ± 0.5% (p=.024) in the control group. Blood levels of epicatechin were significantly elevated in the high-flavanoid group relative to baseline.

Insulin sensitivity was examined in a randomized, controlled study in 61 healthy subjects who consumed high-polyphenol dark chocolate (20 g containing 500 mg polyphenol) or chocolate with negligible polyphenol content daily. After 1 month, the high-polyphenol group showed significant reductions in insulin levels and homeostatic model assessment insulin resistance (HOMA-IR) and increases in quantitative insulin sensitivity check index (QUICKI) but no change in glucose levels, indicating improved insulin sensitivity. Control subjects had opposite results: increases in insulin, HOMA-IR, and glucose concentrations and decreases in QUICKI.

Reductions in blood pressure have been reported in adults with untreated upper-range prehypertension or Stage 1 hypertension without concomitant risk factors. In a randomized, controlled, investigator-blinded study, 44 adults were randomized to either 0.2 oz of dark chocolate (30 mg polyphenols) or matching white chocolate (no polyphenols) daily for 18 weeks. In the dark chocolate group, mean systolic and diastolic BP values were significantly reduced from baseline to Week 18. The proportion of these subjects who were considered Stage 1 hypertensive declined from 86% to 68%, and sustained increases in the plasma biomarker S nitrosoglutathione were seen. In the white chocolate (control) group, BP and plasma biomarkers did not change.

Low-density liprotein (LDL) oxidation lag time was 8% greater when chocolate (22 g of cocoa powder and 16 g of dark chocolate, providing 466 mg of procyanidins daily) was added to a standardized diet in a randomized, 2-period, crossover study involving 23 healthy subjects. The diet was standardized for fiber, caffeine, and theobromine. Each period lasted 1 month with a 2-week washout period. Serum total antioxidant capacity measured by oxygen radical absorbance capacity was significantly greater (~4%) after chocolate and was correlated with LDL oxidation lag time. High-density lipoprotein (HDL) cholesterol was 4% higher after chocolate, but LDL/HDL ratios were not significantly different for the chocolate and no-chocolate periods.

Platelet activation was assessed in human blood samples collected before and 2 and 6 hours after ingestion of a cocoa beverage, caffeine-containing control, or water, as measured by expression of activation-dependent platelet antigens and platelet microparticle formation along with primary platelet-related hemostasis. Results showed that cocoa suppressed adenosine diphosphate (ADP)- or epinephrine-stimulated platelet activation and platelet microparticle formation. Cocoa had an aspirin-like effect on primary hemostasis.

Current research: In June 2015, a long-term, controlled, randomized, blinded study called COSMOS (cocoa supplement and multivitamin outcomes study) sponsored by NIH, Mars, and Pfizer began enrollment. A total of 18,000 subjects (60+ years of age) will be treated for 4 years with pills containing cocoa supplement or placebo; subgroups will receive multivitamins or matching placebo. Primary outcomes measured will include major cardiovascular and cancer events.

Concluding thoughts: It's no wonder that headlines have lauded the cardiovascular health benefits of chocolate in recent years. However, it's important to remember that results from observational studies, even if they are huge, are, at best, associations. As additional results come in from well-designed, randomized, blinded, controlled studies, the evidence strengthens. Still, if the benefits are coming from flavanols, I'm inclined to reach for them packaged in something other than sugar and fat, for example in green and black teas or in beans. Or perhaps in pill form: A Swiss company, Flaviola is interested in marketing a cocoa product that avoids the degradation of flavanols in processing and the downsides of sugar and fat.

But...if I end up having "Death by Chocolate" for dessert, I can assuage my guilt by realizing I've just done my heart a big favor.

Blogger: Ginny Fleming, Founder, Lucidize Medical & Scientific Editing. Chief capacities: medical, scientific, and technical writing and editing.