Caffeine & Insomnia related:

• Tea contains caffeine (equivalent to 1/4 cup of coffee). 
• It is therefore not recommended for people who are over-sensitive to caffeine.
  
• Interestingly, some research on de-caffeinated green tea showed that most of the health benefits disappeared with the remove of the caffeine.

• Similalry for those who suffer from insomnia, avoid drinking tea in the afternoon. 
  

Iron Deficiencies:

• Tea reduces the absorption of iron.
  
• Therefore , for those who are iron deficient, it is recommended not to drink tea with meals.