Dark chocolate has a higher percent of actual cocoa compared to milk and white chocolate. The higher level of cocoa is what gives the health benefits of dark chocolate.
The potential drawback to dark chocolate is it is the most bitter of the chocolates. The higher the percent listed on dark chocolate, the higher the amount of cocoa and more bitter taste (and potential health benefit) it will have.
Dark chocolate is often touted as a health food or even superfood that can positively impact your health. However, there are some potential drawbacks of dark chocolate that should be considered before relying too heavily on it for any health benefit.
Here is a closer look at some of the pros and cons to consider with dark chocolate.
Pro 1: Antioxidant Source
Antioxidants are compounds in food that can provide protection to body cells from damage and may help protect against chronic diseases. Flavanols are an antioxidant source found in plant foods such as fruits, vegetables, red wine, tea and especially cocoa.
Many studies have found an inverse association with flavanol intake and risk for cardiovascular disease and type 2 diabetes. Therefore, since cocoa is a good source of flavanols, it could be concluded eating dark chocolate could provide this benefit. However, the manufacturing and processing of chocolate which involves fermentation, drying, roasting, nib grinding and tempering of cocoa beans can all lower the antioxidant level in chocolate. Cocoa beans have the highest level of antioxidants, but the level of antioxidants in the dark chocolate bar you eat can vary.
Pro 2: Heart Health
Many (but not all) studies have shown dark chocolate may provide heart health benefits. A 2018 study had research participants consume either 2 grams of 70% dark chocolate or 2 grams of milk chocolate daily. At the end of 6 months, the dark chocolate group significantly lowered blood pressure, total blood cholesterol, triglycerides, and LDL-cholesterol.
A 2015 study found daily intake of dark chocolate (25 grams) lowered blood pressure and fasting blood sugar after 8 weeks compared to participants who had 25 grams of white chocolate daily. A 2012 study with data from over 37,000 men over 10 years concluded moderate chocolate consumption may lower risk for stroke.
One reason dark chocolate is associated with lowering blood pressure is its effect on dilating blood vessels after eating. A by-product of ingesting cocoa is the release of nitric oxide into the bloodstream which helps blood vessels open which in turn helps lower blood pressure.
What the Biggest Trial Found
It is worth keeping all of that in mind when reading headlines about studies claiming dark chocolate is good for your heart. The largest and most rigorous study to date actually tested a cocoa extract supplement (providing 500 mg cocoa flavanols, including 80 mg epicatechin, per day), rather than chocolate, and its findings were a bit mixed.
In a randomized, double-blind, placebo-controlled study published in 2022, researchers in the U.S. gave 21,442 people either a cocoa extract supplement or a placebo (dummy) pill. (No one in this study was asked to eat chocolate.) That was 12,666 women age 65 and older and 8,776 men age 60 and older. All were without self-reported heart attack or stroke or recent cancer diagnosis at enrollment, and they took the pills between June 2015 and December 2020. The primary goal of the study was to find out whether the supplement could reduce overall cardiovascular events. There were 410 such events among people who took cocoa flavanols and 456 among people taking the placebo, a difference of only about 10% that wasn’t statistically significant. But when researchers looked at a secondary (but pre-planned) outcome of their study, they did find that cardiovascular deaths were significantly (by 27%) lower among people randomized to take cocoa flavanols. And among participants who took their study pills as they were supposed to, there was also a statistically significant reduction (by 15%) in overall cardiovascular events.
So the link between cocoa flavanols and heart health is not built on nothing, but it rests on shakier ground than the headlines suggest.
Pro 3: Brain Function
The nitric oxide that relaxes blood vessels to lower blood pressure can also have a positive effect on brain function. Nitric oxide from ingesting cocoa has been shown to increase blood flow to neurons in the brain. This increased blood flow provides oxygen as well as increased removal of waste products in the brain.
Could eating dark chocolate make you smarter? A 2012 paper indeed found a correlation between chocolate consumption and the number of Nobel laureates per capita. However, a critique of this study is this correlation is on a population basis and did not track the actual intake of chocolate from the Nobel laureates specifically. It is important to remember correlation does not mean causation, and this paper is of course not really suggesting dark chocolate increases the chance of getting a Nobel prize.
Dark chocolate may also positively impact brain function with improving mood and lowering stress. Research has shown consuming 70 percent dark chocolate could have a positive effect on mood, stress and memory. More research is needed for this potential brain benefit effect.
Remember, while dark chocolate could have a positive role in brain function, stress and mood, there are of course many other factors that also impact these.
Pro 4: Source of Minerals
Cocoa is a source of minerals including: magnesium, copper, potassium and iron. Many Americans do not get enough magnesium or potassium in the diet, so adding dark chocolate to the diet could help contribute to meeting these daily intakes. In fact, it is estimated about half of Americans may be deficient in magnesium and most American adults fall short of recommended potassium intake.
Cocoa is not the only food to provide these nutrients, and many foods can offer higher amounts of these nutrients as well. Other foods that provide these minerals include: vegetables, fruits, nuts/seeds, red meat and egg yolks.
What Is Actually in an Ounce
According to the US Department of Agriculture food composition database, one ounce (about 28 grams) of dark chocolate (70-85% cacao solids) provides 170 calories, 12 g fat (6.9 g of that is saturated), 3.1 g fiber, 65 mg magnesium, 203 mg potassium, 3.4 mg iron, and 0.5 mg copper.
That may not sound like a whole lot, except for two things. First, this is only an ounce. And second, the same serving also has 23 mg caffeine, as well as 227 mg of another stimulant found in cocoa, theobromine, that would probably be noticeable late in the evening.
Still, the minerals are definitely there. And researchers don’t always use an ounce in studies. One trial used just 2 grams of dark chocolate per day. Another used 25 grams, slightly under an ounce, daily.
Pro 5: Gut Health
Cocoa and dark chocolate may have a surprising beneficial role on gut health. A 2013 meta analysis on chocolate and gut health found the antioxidants in cocoa may help probiotic strains grow in the intestine. In this sense, these antioxidants are acting like a prebiotic in helping probiotic bacteria grow.
Keep in mind this does not extrapolate to any chocolate promoting gut health. Sugar and other added ingredients to some chocolate products can have the opposite effect on gut health.
The One That Cuts Both Ways: Bone Health
The combined effects of being a source of antioxidants and providing bone building nutrients like magnesium suggests dark chocolate may be beneficial for bone health. However, chocolate also provides nutrients that may inhibit bone growth such as sugar and a compound called methylxanthines. Methylxanthines are a caffeine-like compound found in cocoa, tea and coffee.
Studies on chocolate intake and bone health are mixed. Some evidence suggests chocolate intake in adolescence may benefit bone growth. However, daily chocolate intake in post menopausal women has been shown to lower bone density.
Con 1: Source of Heavy Metals
Dark chocolate is often highlighted as an antioxidant source, but it is also a potential source of heavy metals cadmium and lead. According to Confectionery News, the European Union implemented maximum limits for heavy metals in chocolate, and California now requires a warning label for products that are higher than 4.1 micrograms of cadmium per serving. However, currently there are no other guidelines for labeling levels in dark chocolate.
What the Heavy Metal Testing Found
Consumer Reports tested 28 dark chocolate bars for their levels of cadmium and lead and shared its results in December 2022. Twenty-three of them carried more lead, more cadmium, or both, than California allows an adult in a single day. Since there are no federal guidelines for levels of these heavy metals in most foods, the group used California’s limits, which are among the strictest and provide the greatest consumer protection.
Only five dark chocolate bars came in under the state’s strict guidelines for daily doses of lead and cadmium: Mast Organic Dark Chocolate, Taza Chocolate Organic Deliciously Dark, Valrhona Abinao, Ghirardelli Intense Dark, and Ghirardelli Intense Dark Twilight Delight. If you eat one ounce a day of any other bar tested, you’d be over the daily limits for at least one of those heavy metals set by California for adults (0.5 micrograms for lead and 4.1 micrograms for cadmium).
The lead limit is eight times stricter than the cadmium one, which is why so many bars didn’t make the cut. That said, the wide spread between bars suggests dark chocolate’s heavy metal problem is more a question of which bar you pick than of dark chocolate itself.
Con 2: Child Slavery
According to Slave Free Chocolate, 2.3 million children work in harvesting cocoa in Ghana and Côte d’Ivoire. Harsh living and working conditions are an unfortunate common occurrence with cocoa harvesting. There have been recent lawsuits against some of the largest chocolate companies from former children slaves. Most of the cocoa supply in the world comes from West Africa; regulations of child slavery have many gaping holes. Ethically grown chocolate is available, but other chocolate products that are not marked may be made from modern day slaves.
Con 3: Lack of Consistency
Chocolate products do not have to label how much antioxidants or heavy metals are in them. Therefore, the amount of both beneficial antioxidants and harmful heavy metals can vary widely in chocolate products. One way to check chocolate products for heavy metals is to check the Consumer Lab list for cocoa and dark chocolates with the least contamination.
Dark chocolate can mean a catch all term for chocolate products having anywhere from 50-90 percent of cocoa. A dark chocolate bar at 50 percent cocoa compared to one at 90 percent of cocoa will not have the same nutrition profile. Check labels for highest cocoa amounts and least amount of added sugar (if you can tolerate the more bitter flavor) for the highest amount of antioxidant potential from dark chocolate.
Summary
Like most foods, dark chocolate has some positive as well as potentially negative effects. Cocoa levels are highest in dark chocolate products which provide a source of antioxidants and minerals. However, dark chocolate products could also be a source of heavy metals and may promote child slavery around the world.
Not all dark chocolates are created equal and can have varying levels of both positive and negative nutrients. For highest levels of antioxidants, choose dark chocolates with higher amounts of cocoa, like over 70 percent. Research companies before purchasing for ethical harvesting practices, and when you eat dark chocolate do so in moderation of a balanced diet.
References:
Magrone T, Russo MA, Jirillo E. Cocoa and Dark Chocolate Polyphenols: From Biology to Clinical Applications. Frontiers in immunology. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5465250/. Published June 9, 2017. Accessed March 14, 2021.
Rostami A, Khalili M, Haghighat N, et al. High-cocoa polyphenol-rich chocolate improves blood pressure in patients with diabetes and hypertension. ARYA atherosclerosis. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4460349/. Published January 2015. Accessed March 15, 2021.
Zugravu C, Otelea MR. Dark chocolate: To eat or not to eat? Journal of AOAC International.https://academic.oup.com/jaoac/article/102/5/1388/5658268?login=true. Published September 2019. Accessed March 15, 2021.
Holly Klamer MS, RDN is a Registered Dietitian and freelance nutrition and writer.
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