The humble cocoa bean
Chocolate has its origins in the humble bean. Like many other beans and plant foods, the cocoa bean is full of phytonutrients (plant nutrients), many of which are antioxidants. In fact, some dark chocolate has more antioxidants per 100g than some berries! Unfortunately not all chocolate is made equal, and the more cocoa in your chocolate the more health benefits you can look to reap from a little indulgence here and there.
For example, white chocolate literally has no cocoa in it – it has only 0.23 mmol of antioxidants per 100g. If you like a dark rich chocolate such as ones that contain 70% or 99% cocoa, you will be enjoying roughly 7.2 and 10.9 mmol of antioxidants per 100g respectively. Just FYI many milk chocolates contain about 40% cocoa solids or less. If you want to know how your favourite chocolate bar (or egg) compares, just have a look at the list of ingredients on the packet – the % cocoa solids should be in brackets next to 'cocoa' in the list.
Chocolate and your heart
Epicatechins are a group of natural antioxidants found in cocoa. These antioxidants are also found in green tea. It's no surprise then that chocolate may have health benefits for your heart. Studies have found that regularly consuming foods with epicatechins can reduce a persons' blood pressure, improve the functioning of their blood vessels, reduce inflammation in the body and reduce the tendency of platelets in blood to clot. Additionally, there is data to suggest that consuming dark chocolate on a daily basis (yum!) can reduce the level of bad cholesterol (LDL) in your blood by 5.3%.
We know these are all positive improvements in risk factors, but do they all relate to an overall reduction in heart disease? You'll be happy to hear that results so far are positive. A study of almost 20,000 participants found that those who ate more chocolate were almost 40% less likely to suffer a heart attack or stroke over a period of eight years compared to people who ate less. Interestingly, these benefits were evident with as little as 7.5g of chocolate a day (the average chocolate bar is usually around 50g). 
Chocolate and your memory
In the same way that chocolate can improve the flow of blood through the heart and body, studies have suggested that it can improve the flow of blood through the brain. Potentially, this could lead to reduced rates of dementia, but more research is required to confirm the association.
In addition to epicatechins, cocoa is also full of polyphenols! In recent years there has been a lot of research on the effect of polyphenols on memory and cognition. Studies so far indicate that polyphenols may improve acute memory when given in high doses, as well as long-term memory when consumed regularly. The effects are so quick that a study conducted in the UK found that consuming chocolate before a simulated driving task improved performance compared to either having no snack or the same amount of calories consumed as a snack of cheese and biscuits. 
If you're not a chocoholic, not to worry. You don't need to miss out! Other foods that are high in polyphenols include fruits, coffee, wine and tea.
Other effects of chocolate on your health
Without wanting to go on and on, there is some data to suggest that the antioxidant effects of cocoa may help to reduce insulin sensitivity and hence diabetes, as well as protect nerves from injury and inflammation, protect skin from UV damage and lastly, improve mood (though we all could probably have predicted that one!). [2, 6]
While I would like to say that the research says all of our meals should consist of chocolate – it's just not the case. What they do indicate however is that a little chocolate here and there, particularly dark chocolate, may help keep us healthy. As one study so nicely summed it up: 'research to date suggests that the benefits of moderate cocoa or dark chocolate consumption likely outweigh the risks'.
 Carlesn MH, Halvorsen BL, Hoite K et al. The total antioxidant content of more than 3100 foods, beverages, spices, herbs and supplements used worldwide. Nutr J. 2010; 22: 9
 Corti R, Flammer AJ, Hollenberg NK, Lüscher TF. Cocoa and Cardiovascular Health. Circulation. 2009; 119: 1433-41.
 Allen RR, Carson L, Kwik-Uribe C, et al. Daily consumption of a dark chocolate containing flavanols and added sterol esters affects cardiovascular risk factors in a normotensive population with elevated cholesterol. J Nutr. 2008; 138: 725.
 Buijsse B, Weikert C, Brogan D et al. Chocolate consumption in relation to blood pressure and risk of cardiovascular disease in German adults. Eur Heart J. 2010; 31: 1616-23.
 Smith AP, Rich N. Effects of consumption of snacks on simulated driving. Percept Mot Skills. 1998; 87: 817-8
 Kats DL, Doughty K, Ali A. Cocoa and chocolate in human health and disease. Antioxidants and Redox Signalling. 2011; 15: 2779-2811