Coffee and tea contain methylxanthines, which cause temporary increases in the natural production of vasopressin, a hormone produced by the pituitary gland. Vasopressin causes clumping of blood cells, and the clumping is more pronounced in women than in men. This is probably the explanation of the fact that women face as much as a tenfold higher risk than men do of complications following angioplasty, a technique used to clear clogged arteries.
Prior to undergoing angioplasty, women should avoid coffee and tea is most strongly supported by the information above.