April 1st, 2011
10:09 AM ET
Every weekday, a CNNHealth expert doctor answers a viewer question. On Friday, it's Dr. Melina Jampolis, a physician nutrition specialist.
Asked by Becca from California
I was wondering what the professional opinion on Vitamin Water is. How can it be zero calorie when it has over 5g of carbohydrate per serving? Also, should I be concerned about vitamin toxicity? I know most of them are water soluble, but could I accidentally be consuming a dangerous amount of things like vitamin C?
Rather than commenting on a specific product, I'll respond instead by discussing water, or any beverage for that matter, with added vitamins. Regarding your calorie question, many of these zero-calorie products contain sugar alcohols (sweeteners that end in "ol"), which are considered carbohydrates but are not metabolized by the body, so they do not contribute to the total calorie count of a product.
Regarding vitamin toxicity, the active vitamin levels that you are actually consuming are probably much lower than what is listed on the label. According to Diane L. McKay, Ph.D., FACN assistant professor, Friedman School of Nutrition Science and Policy, water-soluble vitamins, which include vitamin C and all the B vitamins, can degrade when they are subjected to water for a prolonged period. If you also subject them to heat and, for some, light, they will degrade even more rapidly.
In addition, the fat-soluble vitamins, which include A, E, D and K, are not absorbed unless they are consumed with fat. So unless you consume fortified beverages with a meal or a snack that contains some fat, you will not absorb any of these added vitamins. One exception is when vitamin D is added to fat-free milk or orange juice. In this case, the vitamin D is encapsulated to improve absorption.
Because the vitamin levels your body is absorbing are likely considerably less than what is listed on the bottle, vitamin toxicity from beverages alone is probably not a significant risk. However, it is worth considering in terms of total daily vitamin intake, especially when you take into account how many fortified foods Americans consume and how many of us take a daily multivitamin and additional dietary supplements. McKay notes that "When you consider how much you already get from other sources in your diet, you could be getting too much of a good thing. For some vitamins, like B1 (thiamin), B2 (riboflavin), and B12 there are no negative health effects of consuming high amounts. For others, like folate (or folic acid), niacin, B6, C, as well as all of the fat-soluble vitamins, the consequences of getting too much can range from something like diarrhea to irreversible nerve damage, or even liver damage."
So in my opinion, these products are not dangerous, but they are not a health food either (beyond the fact that they contain water). Nutrients should be consumed as close to their natural state as possible to ensure that you get all the potential health benefits. If products like this help you consume more water and don't drain your pocketbook, then enjoy them, but don't consider them a substitution for a diet rich in fruits and vegetables. And limit sugar-filled water and beverages, fortified or not, as these simply add rapidly digested calories to our already calorie-dense diets.
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