Recent interest in the health benefits of chocolate was sparked by studies on the cocoa-drinking peoples of Central America.
Researchers observed that the Kuna Indians of Panama, who drank cocoa as their main beverage, had very low blood pressure, a leading cause of heart disease and stroke.
Chocolate is the processed and sweetened food produced from cocoa. Cocoa is a good source of iron, magnesium, manganese, phosphorous and zinc. It also contains the antioxidants catechins and procyanidins.
Brand experts have sought to associate chocolate – and in particular dark chocolate – with the supposed health benefits of cocoa, which include protection against cancer and stress relief.
We've teamed up with the British Dietetic Association (BDA) to examine whether the health claims made about chocolate are supported by the evidence.
The evidence on chocolate
Can chocolate reduce blood pressure?
A well-conducted 2012 review of the best available evidence on the effects of chocolate on blood pressure concluded that cocoa products – including dark chocolate – may help slightly lower blood pressure.
However, most of the studies were of short duration (between two and eight weeks) and there were some weaknesses in the available research.
The authors of the review say longer-term trials are needed to further our understanding of cocoa's effect on blood pressure and cardiovascular health.
Can eating chocolate prevent cancer?
Some limited animal and laboratory research suggests a cocoa-rich diet could offer protection against bowel cancer. But it's impossible to conclude from research carried out in a laboratory that cocoa can protect people against bowel cancer.
Does chocolate stop stress?
In a small study from 2009, 30 healthy people who were given 40g of dark chocolate a day for 14 days experienced a reduction in stress hormones. However, the study, which was funded by a major chocolate manufacturer, had several limitations, including its short study period, and does not provide any evidence chocolate has any benefits or effects on stress.
Do two chocolate bars a day prevent stroke?
A recent study carried out in Norfolk in 2015 looked at chocolate consumption and cardiovascular disease. It reported people who ate the equivalent of two chocolate bars a day had a slightly lower risk of stroke than people who never or rarely eat chocolate.
But this study failed to establish a direct cause and effect relationship, as there was evidence the chocolate eaters were healthy in other ways. Similarly, people who never eat chocolate may do so if they were advised to avoid it because of health reasons.
Can venous leg ulcers be helped with chocolate?
Venous leg ulcers are open sores that can develop on the leg or foot, and can take many weeks to heal. People who find it difficult to move around as a result of conditions such as obesity or paralysis are particularly at risk.
A 2013 review looked at whether flavonoids, a compound found in chocolate and red wine, could help accelerate wound healing. The study only found weak evidence, so it is unclear how flavonoids compare with existing treatments.
The dietitian's verdict on chocolate
Alison Hornby, a dietitian and BDA spokesperson, says it's important to remember the studies on the health benefits of chocolate have focused on cocoa extracts, not chocolate.
She says: "A range of health benefits from the consumption of cocoa products have been investigated, particularly in relation to cardiovascular disease, with early results showing promise.
"However, the potential health benefit of some compounds in chocolate have to be weighed against the fact that to make chocolate, cocoa is combined with sugar and fat.
"This means chocolate is an energy-dense food that could contribute to weight gain and a higher risk of disease. As an occasional treat, chocolate can be part of a healthy diet. Eaten too frequently, it is an unhealthy choice."