We always seem to hear how good green tea is for us and I have no intention of taking away from that. One of the best things we can do for our health is to drink green tea daily. But let's not forget about black tea. Studies, one from the University College in London particularly, have found that black tea lowers the levels of the stress hormone cortisol. People in the study who included black tea in their diets were more relaxed and able to complete difficult tasks. Feeling stressed, relax with a good cup of black tea.