I've mentioned before that I grew up in the Pennsylvania Dutch culture, and one can't grow up in that culture without learning how to be thrifty. Multi-use items appealed to our sense of thrift, so when someone starts spouting the many virtues of vinegar when it comes to cleaning and/or food preparation, it actually brings back fond memories of how creativity in day to day living was encouraged (creativity of thought not so much, but that is another story). When people (like our friend Dr. Oz) start talking about vinegar being a super food, or start touting how it "cures" everything from high blood pressure to high blood sugar, then I start to wonder if some one's creativity has overstepped its bounds. Is there any evidence that consuming vinegar on a daily basis or taking supplements can actually improve any particular health conditions?
Let's start with the somewhat good news. If you have Type 2 diabetes, there is some evidence that including 2 tablespoons of vinegar per day (in the evening) might improve your morning blood sugar, particularly if your blood glucose readings are already in decent control (Link). Unfortunately, most of the research done on this topic (including the linked article) includes a pretty small sample size, and we don't know if it helps with people who have poorly controlled blood sugars. If you are already working hard at controlling your blood glucose levels through carbohydrate control (diet), exercise, and medication/insulin (if applicable) and you wanted to try adding vinegar to your regimen it probably wouldn't hurt, but we don't know how much it might help until we do more research.
When it comes to weight loss, the news it also somewhat good if very, very tentative. Back in 2005 there was a small study (as in only 12 people) done which indicated those who consumed vinegar with their white bread felt more satiated (aka "full") after eating (and they had better blood glucose levels too). Once again, since the study is so small we really can't extrapolate that to a larger population. I can also hear those who are controlling their blood glucose levels with a controlled- carbohydrate eating plan saying "Why don't you just avoid the white bread?" in a fairly grumpy tone of voice, and I have to say I both agree with that statement and sympathize with those who might still want to eat white bread sometimes and minimize the damage. There is more research to support controlling carbohydrate intake for blood glucose control than there is vinegar, however, so cheaters beware on this one.
When it comes to using vinegar to prevent cancer, lower blood cholesterol levels, or lower blood pressure (a particularly popular folk remedy among my patients), the news is only positive if you are a lab rat as there haven't been any good human studies done. Some observational studies indicate that people who consume salad with oil and vinegar on a regular basis have a lower risk of heart disease, however, correlation does not equal causation. Improving your intake of potassium rich vegetables can help improve blood pressure; so if you are more willing to eat vegetables when they have vinegar and a healthy olive oil on them, please do so.
If you can't resist adding vinegar to regimen to help with your blood glucose levels and/or your weight, I would suggest that you either take it straight (if you can stand it) or just add it to your food (which I personally would prefer). Any time you take a supplement you run the risk of spending more money, taking something that doesn't even contain the listed amount of ingredients, or you take more than a person would normally be able to eat and we don't know what problems that might cause down the road. (Safe doses do seem to be pretty high on this one at least.)
Take home message--if you use vinegar as part of your plan to increase your vegetable intake that part alone might help with your weight loss, etc, but don't expect the vinegar to help on its own.