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Dear Doctor: What are the benefits of apple cider vinegar? I hear about it on social media, but I don't understand how vinegar can lead to weight loss or help me control my blood sugar.

Dear Reader: My mom is a big proponent of apple cider vinegar. She likes to put it on her salads and vegetables, or just drink a spoonful of it. I am somewhat dubious about her claims of its health benefits, but I am also skeptical of my own resistance to accepting her belief.

Vinegar is created by the fermentation of many natural substances, including grapes, sugar cane, rice and, in this case, apples. The fermentation process produces acetic acid of various concentrations. With apple cider vinegar, the acidity is fairly high -- at a pH of about 3 on a scale of 0 to 14 (a pH of 1 to 7 is acidic).

Apple cider vinegar also contains many polyphenols, or plant-based compounds. These antioxidant compounds have been shown to decrease blood pressure in laboratory animals, improve the ability to metabolize sugar and have beneficial effects on cholesterol.

Now let's analyze the potential medical benefits of apple cider vinegar. In one interesting study, researchers removed the ovaries of mice to increase their oxidative stress and to mimic menopause; then they fed the mice a high-cholesterol diet. One group of mice was given apple cider vinegar, while another group was not. The mice given apple cider vinegar had improvements in their cholesterol; a decrease in the oxidation of LDL, the so-called "bad" cholesterol; and an increase in the antioxidant glutathione. However, there were only 10 mice in each of the groups, so the numbers don't carry much power.

In a French study of rats fed a high-fat diet and apple cider vinegar, researchers found a decrease in blood sugar and benefits in all cholesterol numbers -- triglycerides, LDL cholesterol and HDL cholesterol. Researchers also found in the apple cider vinegar group a decrease in food intake and a decrease in body weight. The authors proposed that apple cider vinegar had an effect of reducing appetite. Again, the number of rats in the study was small, with only six in the apple cider vinegar group.

Obviously, rodents are not humans, but that said, many studies of humans have shown that vinegar reduces the glycemic response and the glycemic index of sugars and carbohydrates. Vinegar itself may help lower blood sugar, but the mechanism of action is not understood.

Along those lines, a 2004 study looked at 11 patients who had insulin resistance and 10 patients who had Type 2 diabetes. Compared with a placebo, apple cider vinegar improved patients' insulin sensitivity, meaning that it improved insulin's ability to bring sugar out of the bloodstream and into the cells of the body. Also, apple cider vinegar decreased the rise of both sugar and insulin when the subjects were given a bagel and orange juice -- normally insulin- and glucose-spiking foods.

Lastly, in a Swedish study of 12 healthy males given bread both with and without white vinegar, those who consumed the vinegar showed a lowering of blood sugar and insulin. Those who consumed the vinegar also felt full more quickly.

So the benefit of apple cider vinegar may be in vinegar itself, not anything specific to the vinegar from the fermentation of apples. But because the studies above didn't all concern humans and weren't conducted long-term, it's difficult to make a conclusion about the benefits of apple cider vinegar or any other vinegar.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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