Chocolate, obtained from beans of Theobroma cacao, has been consumed for centuries.
Dark chocolate is gaining interest as a potential functional food with numerous health benefits in the last decade.
It contains flavonoids, magnesium, and theobromine that have antioxidant, anti-inflammatory, and antiplatelet activities.  
Health Benefits of Dark Chocolate
The key benefits of dark chocolate include lowering blood pressure in mild hypertensive, obese individuals, and improving cognitive functions. It may modulate serum lipid markers, protect skin health, and reduce insulin resistance. It may also reduce the risk of preeclampsia and lower exercise-induced oxidative stress.
1. Dark chocolate lowered blood pressure in hypertensive and overweight individuals
Dark chocolate consumption reduced systolic and diastolic blood pressure in prehypertensive or hypertensive individuals.  
Cocoa flavonoids improved endothelial function by enhancing nitric oxide synthesis and thereby may decrease blood pressure.
In a randomized controlled study, 6.3g of dark chocolate reduced mean systolic and diastolic blood pressure in adults with untreated prehypertension or stage 1 hypertension.
The ingestion of dark chocolate improved endothelial function and lowered blood pressure in overweight individuals. 
A meta-analysis showed that ingesting cocoa-rich foods reduced blood pressure compared to the placebo.
What it means: Several studies showed that dark chocolate reduced systolic and diastolic blood pressure in hypertensive and overweight individuals. More significant, longer-duration clinical trials are required to confirm the benefits of dark chocolate in lowering the risk of cardiovascular diseases.
2. Dark chocolate improved cognitive function
Chocolate consumption enhanced cognitive function by increasing theobromine levels. 
Cocoa flavonoids may penetrate and accumulate in regions of learning and memory in the brain, thereby improving cognitive function.
Consumption of dark chocolate containing 720 mg cocoa flavanols showed improved spatial memory and performance on aspects of choice reaction time task.
A study involving young adults aged 18-24 years showed that consumption of 35g dark chocolate bar increased verbal memory performance.
In another study, consumption of dark chocolate for 30 days increased nerve growth factor,
theobromine levels, and thus enhanced cognitive function.
Dark chocolate (70%) enhanced neuroplasticity, cognitive processing, learning, memory, and recall.
What it means: Studies suggested that dark chocolate consumption improved cognitive functions, including verbal memory and executive function. Further exploration of the effect of dark chocolate on different aspects of cognitive function is warranted.
3. Dark chocolate may modulate serum lipid markers
Studies showed that dark chocolate might modulate serum lipid markers.
A randomized controlled study showed that the average American diet comprising of 22g cocoa powder and 16g dark chocolate reduced LDL cholesterol and increased total antioxidant capacity, HDL cholesterol concentrations.
A meta-analysis review showed that dark chocolate consumption for 2 to 12 weeks reduced serum LDL and total cholesterol levels.
It did not have any significant effects on HDL cholesterol and triglycerides levels.
A study showed that 75g of dark chocolate increased HDL cholesterol and decreased LDL cholesterol levels in non-smoking, healthy volunteers.
What it means: Dark chocolate consumption may decrease LDL cholesterol, total cholesterol, and increase HDL cholesterol levels. Future randomized controlled studies will determine the role of dark chocolate consumption in the pathophysiology of diseases through its lipid modulating properties.
4. Dark chocolate may protect the skin
Studies showed that consumption of dark chocolate rich in flavanols increased protection to harmful UV rays and decreased transepidermal water loss.
A double-blind study showed that high flavanol chocolate intake offered significant photoprotection from harmful UV effects after 12 weeks. 
It increased dermal blood flow and elevated oxygen saturation.
The ingestion of high flavanol cocoa increased blood flow to cutaneous, subcutaneous tissues, and improved skin hydration by inhibiting transepidermal water loss.
Dark chocolate consumption for four weeks can reduce acne and inflammatory papules.
What it means: Some studies showed that dark chocolate is rich in bioactive components that may protect the skin from harmful UV effects, decrease transepidermal water loss, and prevent skin roughness and acne. Further research studies are required to understand the mechanisms by which components of dark chocolate protected the skin.
5. Dark chocolate may reduce insulin resistance
Studies showed that dark chocolate might reduce insulin resistance by improving endothelial function and reducing oxidative stress.
Eating flavanol-rich dark chocolate for 15 days reduced insulin resistance in hypertensive patients.
A study showed that consumption of chocolate more than once per week for five years showed reduced odds of developing type II diabetes.
Physician’s Health Study showed that chocolate consumption was inversely associated with the incidence of diabetes mellitus in younger and normal body-weight men.
What it means: Consumption of dark chocolate may improve insulin sensitivity by reducing oxidative stress. Also, dark chocolate intake may reduce the risk of developing diabetes. Prospective future studies will determine if dark chocolate ingestion can lower insulin resistance and manage diabetes.
6. Dark chocolate may reduce the risk of preeclampsia
Few studies showed that dark chocolate consumption during pregnancy might reduce the risk of preeclampsia.
A cohort study showed that chocolate consumption (5+servings per week) during pregnancy reduced the risk of preeclampsia.
Another study showed that chocolate intake during the first and third trimester reduced the risk of preeclampsia. First-trimester chocolate consumption also reduced the risk of gestational hypertension.
What it means: Few studies showed that dark chocolate intake during pregnancy might reduce the risk of preeclampsia. The consumption during the first trimester was inversely proportional to the odds of developing gestational hypertension. Additional prospective studies are required to verify the protective effects of dark chocolate intake on reducing the risk of preeclampsia.
7. Dark chocolate may reduce oxidative stress in athletes
Studies showed that dark chocolate consumption might reduce exercise-induced oxidative damage.
A study showed that dark chocolate intake for 30 days increased antioxidant power and reduced muscle damage markers.
It did not, however, affect exercise performance.
Acute cocoa flavanols intake increased antioxidant capacity in healthy cyclists but did not improve recovery.
What it means: Dark chocolate consumption may reduce oxidative stress-induced during exercise. Further experimental studies are needed to clarify the role of dark chocolate in reducing exercise-induced oxidative stress.
Possible Side effects of dark chocolate
Consumption of dark chocolate is possibly safe for most people.
Dark chocolate contains cocoa, and eating more amounts of cocoa may cause nervousness, sleeplessness, fast heartbeat, and increased urination. It may sometimes cause nausea, intestinal discomfort, gas, constipation, and migraine headaches.
Safety aspects of dark chocolate
Eating dark chocolate in large amounts during pregnancy and breastfeeding is possibly unsafe.
Avoid consuming dark chocolate if having anxiety, bleeding disorders, heart conditions, diarrhea, GERD, glaucoma, IBS, irregular heartbeat, and migraine headaches.
Possible Drug Interactions with Dark Chocolate
Caffeine in dark chocolate may interact with several drugs. It may interact with estrogens, lithium, beta-adrenergic agonists, antidepressants, antidiabetic drugs, and theophylline.
Adenosine, clozapine, dipyridamole, and ergotamine may moderately interact with caffeine.
Dosage of Dark Chocolate
There is no optimal recommended dose of dark chocolate. About 25-40g of dark chocolate containing 85% of cocoa is used in the clinical studies to produce a beneficial effect.
Historically, chocolate consumption has been linked to improving women’s sexuality. A study showed that participants who ate chocolate had a higher total desire domain Female Sexual Function Index score compared to women who did not eat chocolate. Additional studies are required to examine the aphrodisiac properties of consuming dark chocolate.
Dark chocolate has high cocoa content with low sugar. It offers benefits to cardiovascular health, enhance cognitive function, and reduce insulin resistance. White chocolate contains sugar, cocoa butter, and milk solids. It did not have any effect on improving mood.  The studies evaluating the benefits of white chocolate are scarce.
The exact mechanism of action of dark chocolate on gut health is not known. A study showed that 40g of dark chocolate consumption modified metabolic profile and the gut microbial activity. It modulated intestinal microbial species as prebiotics and probiotics. More studies are required to examine the effect of consuming dark chocolate on improving gut health.
A preliminary study showed that dark chocolate consumption improved contrast sensitivity and visual acuity. Another study showed that eating dark chocolate did not have any short term effects on visual function. Future prospective trials are required to assess if dark chocolate consumption can help with improving eyesight.
Dark chocolate consumption is gaining popularity for providing several health benefits. It has been associated with lowering blood pressure, serum cholesterol levels, insulin resistance, oxidative stress, and markers of inflammation.
There are not enough extensive studies examining the health-related benefits of dark chocolate. Therefore, future studies will provide a definitive answer about the benefits of taking dark chocolate.