Tuesday, 21 Oct 2014 08:28 AM By Mehmet Oz, M.D. and Michael Roizen, M.D.

England’s first book of etiquette, “The Book of the Civilized Man,” set behavior standards for 14th-century nobles, and many of the guide’s admonitions are still accepted as good manners today:”When food is hidden in your mouth, let your tongue not minister to words.””Sitting at table as guest, you should not put elbows on table.”

And, of course, “Say thank you to your host.”

In fact, good manners are so important that 700 years later, folks still explore how they affect your relationships and your individual well-being.

A recent Australian study reveals that if you like someone and want to become his or her friend, you should find a good reason to say “thank you.” That makes it much more likely that your new acquaintance will stay in touch with you.

And a Harvard study found that people who were thanked usually looked for new opportunities to be helpful to others, and the good will multiplies. Other research has found that friendships and positive social relationships strengthen your immune system, boost optimism and increase longevity!

So make expressions of gratitude part of your everyday routine. It’s good for your health and self-esteem, and will increase your circle of friends. And to get started, you can give thanks that you don’t have to follow all the etiquette advice from that ancient English text: “Do not attack your enemy while he is squatting to defecate”; “Don’t mount your horse in the hall”; and “if you wish to belch, remember to look up to the ceiling.”