After being customary in Southern Europe, it was introduced to the Americans by Spanish explorers in the 16th century. Today it is cultivated in moderate regions on the five continents. Although the lemon does not prosper in extreme cold or heat, it needs several cold nights while the fruit is ripening to change its colors from green to yellow. It is because of this that lemons in tropical regions tend to be green, as also happens with oranges and other citrus.
However, the most fascinating workings of lemons are its phytochemicals. These are substances that lack any calories, and they are neither vitamins nor minerals. The recent discovery of these substances in foods and their remarkable preventative effects on cancer and other diseases is one of the greatest advances of nutrition science.