For some people, the tannins found in nature can cause too strong of a 'buzz', leading to mild or severe headaches. Tannins are touted as excellent antioxidants. The tea industry is promoting this aspect of tea, as are all other industries whose foods involve tannin. Polyphenols in general are found to lower total cholesterol, and also improve the ratio of LDL to HDL cholesterol. They lower blood pressure, lessen risks of cancer, stimulate the immune system, and have anti-bacterial properties.
Tannins tend to bind starches while being digested.
These starches are needed by the body to produce serotonin. In some people, who are extremely sensitive to their serotonin levels, it appears the lack of serotonin can lead to a migraine. Tannin sensitivity is also now thought to be cumulative - a person who begins life with no tannin sensitivities may yet develop one as he or she ages. People who are sensitive to tannins need to moderate their intake of tannins in all forms, and also be sure to eat a reasonable amount of food while ingesting tannins, so the binding affects of tannins do not cause undue stress. We also have a calendar of wine events in Japan.