Polyphenolic compounds like those found in dark chocolate and coffee offer protection.
Cardiovascular disease is a major healthcare burden for the United States. Estimates of total prevalence in the U.S. adult population top 83 million-that’s more than 1 in 3 adults. According to the American Heart Association’s (AHA) Heart Disease and Stroke 2013 Statistical Update, total direct medical costs related to care for cardiovascular diseases are projected to exceed $1.48 trillion annually by the year 2030. Commonly recognized risk factors for cardiovascular disease include obesity, cholesterol and lipid imbalances, diabetes, and compromised blood sugar metabolism.
Another major risk factor for cardiovascular disease is elevated blood pressure.
The concept of elevated blood pressure as a risk factor for cardiovascular disease gained recognition decades ago, when a 30-year follow-up analysis of data (Hypertension, 1989) from over 5000 adults in the Framingham Heart Study revealed that blood pressure levels are a strong predictor for the development of coronary heart disease, congestive heart failure, stroke, and transient ischemic attacks. These associations are further illustrated by AHA estimates that hypertensive blood pressure readings greater than 140/90 mmHg are linked to 77% of first stroke cases, 69% of first heart attacks, and 74% of congestive heart failures.
AHA estimates that nearly 78 million Americans are hypertensive, defined as a blood pressure of >140/90 mmHg. (Normal blood pressure readings are considered to be below 120/80 mmHg.) A review of data from the National Health and Nutrition Examination Survey (NHANES) 1999–2000 estimates that the worldwide prevalence of prehypertension-defined as blood pressure readings in the range of 120–139/80–89 mmHg-is 31%.
The important thing to remember, however, is that blood pressure is modifiable through healthy diet, lifestyle choices, and nutritional intervention-before more drastic alternatives need to be considered.
Polyphenolic compounds from plants have demonstrated significant benefits to the cardiovascular system. While these compounds are likely to have multiple mechanisms of action for cardiovascular health, one mechanism may be to promote the natural ability of the endothelial lining of blood vessels to relax.
Polyphenols also seem to promote beneficial antioxidant effects in blood vessels by enhancing plasma antioxidant levels, decreasing free radicals and their byproducts, and attenuating damage due to oxidative stress. These compounds also influence the activity of endothelial Nitric Oxide Synthase (eNOS), an enzyme that supports healthy nitric oxide (NO) synthesis and availability to the endothelial lining of blood vessels. The availability of sufficient NO in blood vessels is critical to supporting optimal vascular tone by reducing contraction of the blood vessels and inhibiting platelet aggregation for healthier blood flow.
Research on polyphenol-rich foods and food extracts has found some can induce clinical benefits for cardiovascular health and related risk factors, including lowering elevated blood pressure. Two of the most promising foods are dark chocolate and coffee, especially green (unroasted) coffee beans. Flavanols in dark chocolate, and chlorogenic acids in green coffee, show significant promise for enhancing cardiovascular function and exerting protective effects.
Green Coffee and Chlorogenic Acids
Chlorogenic acids are powerful antioxidants found abundantly in green coffee beans but also in many other plants. The term encompasses a number of compounds, including three major subclasses: caffeoylquinic acid, feruloylquinic acid, and dicaffeoylquinic acid. A regular cup of coffee contains between 70 mg and 300 mg of these polyphenols.
A review article by Youyou Zhao and colleagues (Hypertension Research, 2011) from the NestlÃ© Research Center in Beijing highlights the mechanisms by which chlorogenic acids exhibit antihypertensive effects. It also summarizes the pertinent animal and human studies demonstrating blood pressure lowering as an endpoint. According to Zhao, chlorogenic acids influence blood pressure by several mechanisms: 1) direct free radical scavenging activity; 2) inhibition of enzymes, thereby reducing free radical production; 3) stimulation of NO production; 4) inhibition of angiotensin-converting enzyme (ACE) in the plasma and tissues; and 5) anti-inflammatory effects.
While several animal studies show impressive effects on blood pressure with acute and long-term dosing of green coffee extracts, clinical studies are now confirming similar benefits in humans. In a randomized, double-blind, placebo-controlled trial (Hypertension Research, 2005) conducted by Kao Corp. in Tokyo, 117 patients with mild hypertension were assigned to placebo or a daily 180-ml beverage containing 46, 93, or 185 mg of a hot water–extracted green coffee standardized to 54% total chlorogenic acids. After 28 days, blood pressure levels dropped in a dose-dependent manner, with the highest-dose green coffee group showing average reductions of 5.6 mmHg in systolic pressure and 3.9 mmHg in diastolic blood pressure.
In another trial (Clinical and Experimental Hypertension, 2006), conducted by Takuya Watanabe and colleagues in Tokyo, 40 Japanese patients with mild hypertension consumed placebo or 480 mg of a green coffee extract daily (standardized to 140 mg of chlorogenic acids each day). The subjects consumed the green coffee extract in a mixture of fruit and vegetable juice for 12 weeks. At four weeks, average blood pressure reductions in the treatment group were 8 mmHg and 7 mmHg in systolic and diastolic values, respectively. At 12 weeks, average reductions were 10 mmHg and 7 mmHg, respectively.
Green coffee beans should be unroasted because the roasting process otherwise results in the production of hydroxyhydroquinone (HHQ), a compound that seems to antagonize the antihypertensive effect of chlorogenic acids. In animal studies, coffee extract with HHQ has failed to lower blood pressure. When HHQ-free coffee extract was administered instead, the development of hypertension was significantly reduced. Human studies have yielded similar effects.
Flavanols and Dark Chocolate
Flavanols are phenolic compounds present in a variety of foods, and they include catechins and epicatechins. Recent investigations suggest that these substances promote cardiovascular health by enhancing blood flow, with studies showing improved endothelial function and blood circulation throughout the body.
An estimated 10% of cocoa powder’s weight is made up of flavonoids, and finished chocolate is considered to be a most concentrated source of the flavanols catechin and epicatechin. A unique attribute of cocoa flavanols is that they exist as long polymers, whereas catechins found in many other foods are shorter-chain molecules. The long-chain structural properties confer strong free radical scavenging and antioxidant benefits.
Clinical studies on cocoa flavanol intake reveal blood pressure benefits. A meta-analysis (Archives of Internal Medicine, 2007) by Dirk Taubert and colleagues from the Department of Pharmacology at the University Hospital of Cologne in Germany covered five randomized trials in which cocoa products were administered for seven days or more. It found statistically significant average decreases in systolic and diastolic blood pressure levels of 4.7 mmHg and 2.8 mmHg, respectively, in a total of 173 subjects across all studies.
In another meta-analysis (The American Journal of Clinical Nutrition, 2008), conducted by Lee Hooper’s group from the University of East Anglia in Norwich, UK, chocolate intake was associated with reduced systolic and diastolic blood pressure by an average of 5.88 and 3.30 mmHg, respectively.
Kade Davison’s group from the University of South Australia undertook a study (Journal of Human Hypertension, 2010) to assess the effects of differing doses of cocoa flavanols on blood pressure. The study included 32 men and 20 postmenopausal women with untreated mild hypertension (blood pressure greater than 130/85 and less than 160/100 mmHg). Participants were divided into four groups and instructed to consume a daily cocoa beverage, for six weeks, containing 33, 372, 712, or 1052 mg of cocoa flavanols. In only the group consuming the highest dose of cocoa flavanols, significant reductions were seen in mean arterial blood pressure as well as 24-hour measurements of systolic blood pressure (average reduction of 5.3 mmHg) and diastolic blood pressure (average reduction of 3 mmHg).
Verawati Sudarma and colleagues from the University of Indonesia in Jakarta conducted a randomized study (Acta Medica Indonesiana, 2011) in 32 prehypertensive subjects. For 15 days, half of subjects consumed 30 g/day of dark chocolate (flavanol rich) while the other half consumed 25 g/day of white chocolate (flavanol poor). Both groups received dietary counseling in addition to their interventions. Serum levels of NO were assessed at baseline and after 15 days, and they were significantly higher in the group consuming dark chocolate. Blood pressure levels decreased in both groups, but significant improvements were seen in systolic blood pressure levels for the dark chocolate group versus the white chocolate group, with average systolic pressure readings of 120.64 mmHg in the dark chocolate group versus 131.19 mmHg in the white chocolate group. Diastolic readings were also lower in the dark chocolate versus white chocolate group, yet these changes didn’t reach statistical significance.
Lastly, a study conducted in Jordan and led by Saafan A. Al-Safi (Current Drug Delivery, 2011) looked at the relationship between weekly mean intake of dark chocolate and cardiovascular parameters in 14,310 adults. Study participants self-reported their weekly dark chocolate intake and were divided into three groups: mild intake (1–2 bars/week), moderate intake (3–4 bars/week), and high intake (>4 bars/week). Blood pressure readings revealed significantly lower values for subjects reporting the highest consumption of dark chocolate. Blood pressure reductions also appeared linked to increased dark chocolate intake regardless of age or family history of hypertension.
It’s likely that the long-term intake of cocoa flavanols can encourage healthy blood pressure and can significantly impact other aspects of cardiovascular health by improving the function of the endothelium and promoting healthy NO levels. These benefits are likely to extend to other areas as well, including support for brain health by enhancing neural microcirculation and the flow of nutrients to critical tissues. Being selective in choosing healthier chocolate preparations over those with excessive sugar and other additives can go a long way in reaping the benefits of cocoa flavanols without the risks that may be associated with sugar and other additives.