“Lettuce is low in Sodium, and very low in Saturated Fat and Cholesterol. It is also a good source of Thiamin, Vitamin B6, Iron and Potassium, and a very good source of Dietary Fiber, Vitamin A, Vitamin C, Vitamin K, Folate and Manganese” nutritiondata.self.com
Vitamin B6 is naturally present in many foods. The body needs vitamin B6 for more than 100 enzyme reactions involved in metabolism. Vitamin B6 is also involved in brain development during pregnancy and infancy as well as immune function.
This is an interesting link and talks about benefits and a few interactions
And following link is an overview of why lettuce is good for you, not least it helps your heart and helps you relax and helps you to sleep more
Doctors Office. A guy walks into the doctor’s office. A banana stuck in one of his ears, a head of lettuce in the other ear, and a carrot stuck in one nostril.
The man says, “Doc, this is terrible. What’s wrong with me?” The doctor says, “Well, first of all, you need to eat more sensibly.”