BROOKS:would you comment?
Dr. Mercola's Comment re sports drinks:
Now that spring is here and temperatures are beginning to climb upward, I
suspect many of you are itching to get outside and enjoy all the benefits
the extra sun and warmth can do for you and your health. I have been
running for nearly 40 years and it is not only my primary form of
exercise but also a major part of my life. Some of you will also chose
running. 
This is a good thing.
After a good run or heavy-duty dose of weight training, you may be
inclined to reach for one of the many popular "rehydrating" sports drinks
your local gym or supermarket sells. There are many reasons why you
shouldn't, and this study brings up a good one: they can corrode your
teeth. 
This is a bad thing.
Ironically, drinking sports drinks when you exercise and your mouth is
dry is particularly problematic because you don't have enough saliva in
your mouth to combat the drink's acidity. And, if you think fruit juice
or soda are better alternatives, similar corrosive problems have been
found with them too. 
There are situations where wise uses of healthy sports drinks are an
option. However, this is far less than 1 percent of those that use them.
The only indication for these drinks is in those who are vigorously
exercising in cardiovascular aerobic activity for more than 45 minutes or
an hour (at a minimum) and are sweating profusely as a result of the
activity.
Anything less than 45 minutes will simply not result in a large enough
fluid loss to justify using these drinks. But even if you are exercising
for more than an hour I still believe that there are likely far better
options to rehydrate and this new study supports that belief.
This is largely because soft drinks, energy drinks and fruit drinks are
tainted with sugar. Studies have shown that some fruit juices contain as
much as 8 teaspoons of fructose per 8-ounce glass. Additionally nearly
all fruit juices are pasteurized which further damages the fluid. Energy
drinks can contain up to 80 mgs of caffeine and many of the sports drinks
contain high fructose corn syrup. If you aren't aware of the dangers of
fructose please review the excellent AJCN journal article on this topic.
There is a link on the page to the free full text review.
It is also important to know that soft drinks (even the diet varieties)
are harmful because they're loaded with artificial sweeteners like
aspartame. 
In an article I posted about this time last year about thawing out from
the previous winter by spring cleaning your body, the best bet for your
primary fluid is clean, fresh water. 
So by all means, get out there and take advantage of the spring weather
by hiking, jogging, walking, playing tennis--anything to be active. But
leave the sports drinks at home, or, better yet, back on the supermarket
shelf and bring some water with you instead.