I recently visited Hong Kong for the first time. This wonderful city has an attraction unique in the world: ochre-coloured columns of volcanic origin extend in the east of the city down to the ocean. This impressive natural architecture is easily accessible to the public in the Sai Kung Geopark.
Most hexagonal rock columns in other regions of the world are typical basaltic lava. The hexagonal columns in Sai Kung are, by contrast, acidic, silica-rich, rhyolitic volcanic rock. The columns cover an area of over 100 square kilometres (including sea area) and have an average diameter of 1.2 metres.
Hexagonal structures are not rare in nature. For instance, the crystals in our bones and teeth, the apatites, are hexagonal. These apatite crystals contain calcium. The main fraction of calcium of our body is located in bones. Calcium comes from our food, and for its optimal absorption from intestines we need vitamin D.
This vitamin is necessary to prevent the formation of crystals in those places of the body where we do not need them. Without sufficient vitamin D, the risk of calcification of blood vessels and consequent heart attacks increases dramatically.
And where do we get the important vitamin D from?
It has a double character - a vitamin and a hormone. As a hormone it can be synthesised by our body from cholesterol. The synthesis takes place in the skin under UV-B radiation from sunlight.
Basically this should not be a problem for people in Hong Kong but in Germany it is: between September and March, the sun is not intense enough and therefore people at our latitude are not able to produce vitamin D.
The other source is from food. Unfortunately, there are only a few good sources. The best is fish - again not a problem in Hong Kong, but a big one in Germany.
Taking into consideration German sausage eating habits, one can estimate that only one fifth of our daily need is covered. The rest has to be replaced by that one stored in summer in our fat tissue.
However, very often this reservoir is not big enough. About one third of the German population of any age suffers from vitamin D deficiency.
This means an increased risk of osteoporosis but also of heart attacks and perhaps infections.
How to solve this problem? Increase the vitamin D synthesis in summer! This requires a good balance between too much and too little sun exposure as well as sun-protection cream which reduces the effect of UV-B radiation.
And eat more fish. The worst solution is taking vitamin D as a dietary supplement. Take calcium always with enough vitamin D and vice versa.
My message to those sun-averse Hong Kong women: let the sun shine on your precious skin, at least a bit...
Iris Rapoport is a professor of biochemistry at Humboldt University in Berlin