Apple cider vinegar has been purported to increase weight loss and aid in arthritis, asthma, colitis, and even diabetes by lowering blood sugar. Scientific research has been scant. However, recent studies presented in Medscape show that the acetic acid in vinegar really does lower blood sugar by about 7% when used for 12 weeks. It is interesting that eating a pickle can do the same thing, but keep in mind that pickles are soaked in vinegar! The dosage is 2 tablespoons three times a day, which can be used in salads and with many veggies.
The mechanism of action is suspected to be delayed emptying of the stomach, which would lower the rate at which sugar would be absorbed. However, other theories include inhibition of gastric enzymes and inhibition of glucose uptake by muscles.