Sugar, acid and teeth
By Andy Kaiser
Expert analysis by Diane Johnson
Article ID: 1315
I like to multitask. When I listen to other podcasts, I’m not simply staring at my computer speaker or glazing over as my headphones talk to me. I do other things. I browse the web. I drive my car. I may eat, and, as what logically follows, drink.
And it’s that last one – drinking – that’s today’s topic.
I’m a member of the Skeptoid mailing list. (Skeptoid is a podcast created by Brian Dunning. For those who aren’t aware of it, I strongly recommend you check it out.)
There was an interesting discussion on the mailing list. This assertion appeared: “Diet Pepsi is okay [in terms of overall health], but Diet Coke is bad.” As we discussed the issue, others brought up a point: What about tooth decay and really sugary soda pop, like Coke and Pepsi? We know that pop is acidic. It’s probably bad for your teeth. And it’s loaded with sugar, which contributes to tooth decay.
A dentist chimed in to the conversation, saying that in her experience, Mountain Dew is absolutely the worst drink in terms of tooth decay. In her practice, this seems to be the drink of choice for those with enamel wear and decay.
But correlation, as they say, does not imply causation: just because two things appear related doesn’t mean one thing caused the other thing. So the questions remained: What drinks are the worst for your teeth? Instead of using guesses and personal anecdotes, is there a way to objectively measure how bad a drink is for your teeth?
Before we continue, I’ll ask you this question, and we’ll answer it later on in this article. Think about your answer, and see if it matches my test results. Here’s the question: What type of drink do you think is the worst for your teeth? Your choices include pop, coffee, juice, milk, tea, sports drinks and yes, alcohol, including various beers, wines and liquors. After you pick the genre of liquid, can you pick the type or even brand? For example, we’ve already stated pop is bad for your teeth. Do you agree with the previous Mountain Dew assessment? What about Coke products? Or Pepsi versus Cherry Pepsi? And are all these really worse than milk, juice or alcohol?
Think about your answer. I’ll have the results for you soon.
That’s the intent of this article, to find a way to rate the “badness” of drinks in terms of tooth decay. So I ran to the store and purchased dozens of popular drinks. Juices, pop, coffee drinks, sports drinks, milk and a variety of alcohol. I then ran home, eager to test all these liquids. And… I realized I had no idea what to do next.
This is where it helps to know people who are smarter then you. The doctor I mentioned earlier is Dr. Diane Johnson, DDS.
Johnson is full-time practicing orthodontist and has been in private practice since 1986. Her undergraduate degree is a BS in Biomedical Engineering from Northwestern University, her DDS is from Northwestern University Dental School, and her MS is in Orthodontics from the University of Illinois. She reviews for the American Journal of Orthodontics and Dentofacial Orthopedics.
Dr. Johnson says:
“We deal with the harmful effects of dietary choices every day, and since the largest part of our patient population is teenagers, we see a lot of pop consumption.
…my first bit of advice would be to never drink pop! You’ll probably have headaches for 2-3 days while you are withdrawing from the caffeine. Yes, caffeine is extremely physically addictive; one of the ways – like nicotine in cigarettes – that companies make sure you come back for more of their product.
To mitigate the effects of pop consumption, only consume it with meals. Brush soon after eating or drinking anything besides water (including milk or juices).
Chewing gum with xylitol will inhibit plaque bacteria (Trident makes one, but you have to look specifically for the one with xylitol). This will help with the sugar part, but will make no difference with the acid part.”
And this is what we’re dealing with: sugar and acid. Most people know that sugar is bad for your teeth, but not everyone knows about acid.
While designing this experiment, I had to learn at least one new word: “cariogenicity”. Cariogenicity is the measurement of the ability to decay bone or teeth. This is important when we talk about sugar.
Eating sugar feeds a certain type of bacteria (streptococcus mutans). This bacterium, along with other stuff in your mouth, contributes to the formation of plaque. The more sugar you ingest (without cleaning your teeth), the more free dinners you’re giving to streptococcus mutans, and the more eager it is to “go forth and multiply” inside your mouth. This is why brushing your teeth is a good thing – you’ve got to scrape that junk out of there. This is why flossing and using mouthwash are good things – you’ve got to kill off the harmful bacteria.
When I measured the sugar content of various drinks, I looked at the nutritional labeling. I recorded, for example, 65 grams of sugar in a 20-ounce bottle of Classic Coke. But Dr. Johnson knew this wasn’t entirely accurate: not all sugars are the same. Various brands of drinks use various types of sugars. Different sugar types react differently with the bacteria and conditions in your mouth. Sucrose, for example, is a sugar firmly in the “bad” end of the sugar spectrum. On the other end, xylitol is a naturally-occurring sugar substitute that’s not so bad for your teeth.
A sweet drink could contain any type and any combination of various sugars. In order of worst to best, these sugars include:
High-fructose corn syrup
All the liquids involved in this experiment lump together these varieties into the single “grams of sugar” measurement you see on the packaging. If we wanted exact measurements, there are specialized test kits. But the pricing for those is beyond the budget for this experiment. However, the generalized nutritional measurement should still work in determining which drinks are the worst for our teeth. It’s not all about sugar, remember. Don’t forget the acid.
Acidity is measured in “pH“. For this experiment, the pH measurements we’re monitoring fall between 1 and 7. If something has a pH of 1, it’s a strong acid. A pH 1 acid is similar to the stomach acids your body uses to digest that tasty cookie. Moving up the scale, we get less acidic: Lemon juice has a pH of 2. Human saliva has a pH of 7. In terms of your teeth, a pH of 5.5 and above will cause little or no harm. Any pH below 5.5 is bad. At 5.5 and below, a liquid will work to strip the protective enamel from your teeth. You’ve heard the term “tooth decay”? That’s exactly what we’re talking about here – acidic drinks will cause your teeth to literally decay. This is why you hear so much about fluoride: you want it in your toothpaste and water supply because it significantly protects your enamel. There’s also an effect on pH. According to Dr. Johnson:
“Use fluoride toothpaste; rinsing with a mouthwash that contains fluoride is a good idea, too. The presence of fluoride allows the pH to be lower and still not cause enamel dissolution.”
Note that sugar measurement is pretty straightforward – we’re comparing concrete amounts, like “20 versus 30 grams of sugar”. pH is a little different because it’s a base-10 logarithmic scale: say you have two liquids, like Diet Coke and Coke Zero. Diet Coke has a pH of 4. Coke Zero has a pH of 3. Since pH measurements are logarithmic, this means that Coke Zero is ten times more acidic than Diet Coke.
Sugar and acid: the one-two punch of decay
So to summarize: sugar is bad for your teeth. Strong acids are bad for your teeth. High sugar and strong acids together are a bad combination. That combination is what this experiment measures. Here’s what I did:
1) Purchase a whole bunch of drinks. I tried to select liquids that are very popular, picking mostly name brands and the kinds I think a majority of people will drink.
2) Purchase a pH test kit. This is a collection of specially-treated little paper sticks. You dunk them into a liquid, compare the resulting color of the stick to a chart, and that comparison gives you the pH.
3) I took a sample of all my liquids – just an ounce or two. I poured the sample into a paper cup, and I measured the pH.
4) I recorded the sugar content of the drink.
5) After recording everything, I looked at all the bottles and containers now stuffed in my refrigerator, and wondered how in the world I was going to drink it all.
Then Dr. Johnson and I worked to interpret the results. For example, while sugar and acidity are both important, are they equally important when determining the “badness” of a drink? Or should one aspect be given more weight than the other? Thanks to Dr. Johnson for providing the expertise and answering these questions.
Okay, enough detail. Get your answers ready, because here are the results. The picture below provides a summary of the findings, where all liquids tested are listed in order of least harmful to most harmful. You can also download the full dataset in XLS format.
It turns out that the drink that is worst for your teeth is not Mountain Dew. It’s not even a soda pop! It’s a juice. Specifically, grape juice. With a pH of 3, and 88 grams of sugar in 20 ounces of liquid, it’s got the right combination of bad attributes.
I, personally, was disappointed and surprised by this. Why does it have to be grape juice? I love grape juice!
Some other notable results:
Mountain Dew is indeed bad for your teeth, right after grape juice and cranberry juice. Then come Cherry Coke, Pepsi, Classic Coke and Dr. Pepper. These are all worse for your teeth than if you had drunk straight lemon juice.
Moving up the list, we see sweet wines like White Zinfandel. Red Bull makes its appearance, along with more juice, apple cider, and the diet versions of most soda pop. Above that, we see “drier” wines like Chardonnay and Merlot. Above those are beer, then tea. Then we approach the bottled water level. I was surprised to see that bottled water was actually acidic – The Dasani water I measured had a pH of 5.2. Above that, we get fairly safe drinks. Those include coffee (both light, dark and cappuccino-style drinks) and milk.
Our initial premise has been answered: Of the drinks I tested, what’s the worst? Grape juice. Mountain Dew is close, and is indeed the worst of the soda pop.
Like any good scientific test, this experiment helped answer our initial question while raising more interesting questions:
1) Why does Mountain Dew appear to be the most damaging as seen in Dr. Johnson’s dental practice, but it’s not worst on this list? Perhaps because it’s the most popular drink for those who tend to drink a lot of pop and not care as much about their teeth. People are much more likely to drink can after can of Mountain Dew than glass after glass of juice. This may be a testament to Mountain Dew’s superior marketing.
2) Dr. Johnson also expressed surprise at the relatively benign rating for milk. In her practice, she sees a lot of tooth decay in infants, specifically those who are allowed to sleep at night with a bottle of milk hanging out of their mouth. This may be because any liquid is bad for you if you leave it pooling in your mouth long enough. If it has sugar – which milk certainly does – bacteria will love it.
3) After this analysis of acidity and pH, would drinking or rinsing with basic solutions help to neutralize the plaque acids? According to Dr. Johnson, “I am not aware of any research on this; I do know that baking soda is commonly recommended for cleaning teeth but I don’t know if this is due to its acid-neutralizing properties or its mildly abrasive properties.”
As a side experiment, I’m interested what your reaction is to this article. Did you guess right? How did your favorite drink fare? Do you now feel particularly thirsty? Or are you never going to drink juice and pop again? Do you now have a sudden addiction to gum chewing?
Me? I’ve just gotta go brush my teeth.