How much sugar should an adult consume daily?

As little as humanly possible. White refined sugar is very bad for the body. Substitute sugar with Sucanut (comes from the sugar cane, but organic and healthier than refined white sugar because it hasn't lost all nutrients). You can get it at any health food store and sometimes the health section of your grocery store.

It seems sugar is in everything we eat and drink, more now than 100 years ago and Americans are also fatter than ever today. No doubt, sugar is one of the causes.

For your long term health, as little as possible. Complex carbohydrates, such as fruits, vegetables, beans, legumes, and grains, contain all the "sugars" your body needs, without having to consume any simple sugars such as table sugar (sucrose) or soda sugars (in the form of high fructose corn syrup).