It makes sense that too much chocolate would be bad for you because of the high fat and sugar content in most products. But what should we make of common claims that eating some chocolate is actually good for you?

Happily, there is a fair amount of evidence that shows, in the right circumstances, chocolate may be both beneficial for your heart and good for your mental state.

In fact, chocolate – or more specifically cacao, the raw, unrefined bean – is a medicinal wonder. It contains many different active compounds which can evoke pharmacological effects within the body, like medicines or drugs.

Compounds that lead to neurological effects in the brain have to be able to cross the blood-brain barrier, the protective shield which prevents harmful substances – like toxins and bacteria – entering the delicate nervous tissue.

One of these is the compound theobromine, which is also found in tea and contributes towards its bitter taste. Tea and chocolate also contain caffeine, which theobromine is related to as part of the purine family of chemicals.

These chemicals, among others, contribute to chocolate's addictive nature. They have the ability to cross the blood-brain barrier, where they can influence the nervous system. They are therefore known as psychoactive chemicals.

What effects can chocolate have on mood? Well, a systematic review looked at a group of studies which examined the feelings and emotions associated with consuming chocolate. Most demonstrated improvements in mood, anxiety, energy and states of arousal.

Some noted the feeling of guilt, which is perhaps something we've all felt after one too many Dairy Milks.

Health benefits of cocoa

There are other organs, aside from the brain, that might benefit from the medicinal effects of cocoa. For centuries, chocolate has been used as a medicine to treat a long list of disease including anemia, tuberculosis, gout and even low libido.

These might be spurious claims but there is evidence to suggest that eating cacao has a positive effect on the cardiovascular system. First, it can prevent endothelial dysfunction. This is the process through which arteries harden and get laden down with fatty plaques, which can in turn lead to heart attacks and strokes.

Eating dark chocolate may also reduce blood pressure, which is another risk factor for developing arterial disease, and prevent formation of clots which block up blood vessels.

Some studies have suggested that dark chocolate might be useful in adjusting ratios of high-density lipoprotein cholesterol, which can help protect the heart.

Others have examined insulin resistance, the phenomenon associated with Type 2 diabetes and weight gain. They suggest that the polyphenols – chemical compounds present in plants – found in foodstuffs like chocolate may also lead to improved control of blood sugars.

Chocolate toxicity

As much as chocolate might be considered a medicine for some, it can be a poison for others.

It's well documented that the ingestion of caffeine and theobromine is highly toxic for domestic animals. Dogs are particularly affected because of their often voracious appetites and generally unfussy natures.

The culprit is often dark chocolate, which can provoke symptoms of agitation, rigid muscles and even seizures. In certain cases, if ingested in high enough quantities, it can lead to comas and abnormal, even fatal heart rhythms.

Some of the compounds found in chocolate have also been found to have potentially negative effects in humans. Chocolate is a source of oxalate which, along with calcium, is one of the main components of kidney stones.

Some clinical groups have advised against consuming oxalate rich foods, such as spinach and rhubarb – and chocolate, for those who suffer from recurrent kidney stones.

So, what should all this mean for our chocolate consumption habits? Science points in the direction of chocolate that has as high a cocoa solid content as possible, and the minimum of extras. The potentially harmful effects of chocolate are more related to fat and sugar, and may counteract any possible benefits.

A daily dose of 20g-30g of plain or dark chocolate with cocoa solids above 70% – rather than milk chocolate, which contains fewer solids and white chocolate, which contains none – could lead to a greater health benefit, as well as a greater high.