Chocolate and Decompression

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Negros island, where Salaya is located, the farmers in the mountainous hinterland are rowing some excellent chocolate. The Cacao tree is of course of South American origin, but once the Spanish brought this plant to the Philippines it flourished here.

If you visit the Dauin public market, and pass the vegetable, meat and cellphone gadget sections, you’ll get to a row of stands where you can enjoy the traditional Dumaguete breakfast: sticky rice and hot choco. The chocolate is usually dissolved in water (not milk) and

This is certainly a nice way to spend your morning. But it might also be a good way to pre-empt the stresses which diving puts on your body!

In a recent study by Sigrid Theunissen and colleagues, published in Diving and Hyperbaric Medicine, the authors test what effect dark chocolate has on divers. The dives were done in an indoor pool – in Belgium, someone built a 33 meters (!) deep pool, for dive training and experimental studies like this one. All the divers in the study were men – that makes it easier to control for other factors which might have influenced the outcome. 21 of the divers were in a control group, without chocolate, while 21 others were in the “chocolate group”, who ate 30 grams of dark chocolate before the dive. You can probably guess which group of divers I would have wanted to be.

The divers did a 20 minute dive to 33 meters. Before and after the dive, the scientists measured a number of physiological parameters. The most interesting differences between control and chocolate divers was seen in the Flow-mediated-dilation. That’s a measurement of the diameter of the the brachial artery, the major blood vessel of the (upper) arm.

In the control divers, the artery slightly shrank in diameter. In the chocolate divers, it even expanded a bit. This result agrees well with the hypothesis that the high pressure during dives, and the resulting high oxygen partial pressure, causes stress to the endothelial cells (those lining the inside of our blood vessels). The authors conclude that most likely the antioxidants contained in dark chocolate scavenge the free oxygen radicals (dangerous variants of oxygen) caused by high oxygen partial pressure.

Hence, happy chocolate eating AND diving! If you have any questions about decompression physiology, please contact me at


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