What Causes Dry Mouth After Drinking Red Wine?: Tannic Acid Effects on Saliva Production

As many of you probably know from experience, sometimes when you drink a red wine you notice that your mouth gets very dry. This is usually attributed to the tannin levels in the wine—the “bigger” the tannins, the more it seems moisture is wicked away from your mouth and you’re left with something akin to the Sahara happening on your tongue.

So, what is really going on here? Is it the tannins? Why do they make your mouth feel so dry after sipping?

A study published in January in the Open Journal of Stomatology aimed to address a very similar question. In essence, what is the effect of tannic acid in different beverages on glandular function in the mouths of mice?

Quick Background

Before launching into the study and the results, it is important to get a primer on what has been done so far in the world of tannic acid and secretory glandular function so far.

First, the salivary glands in the mouth are basically made up of two different types of parts: those that produce a sort of “preliminary saliva”, and those that absorb salt, and add potassium and bicarbonate to create the final hypotonic saliva. Having this hypotonic property allows the flavors of the food to better pass through the saliva into the taste buds so we can actually taste what it is we are eating or drinking.

It is during the transport of fluids as well as salt, potassium, and bicarbonate that problems with salivary secretions can arise. If something is preventing these processes from occurring, one could be left with excess saliva or alternatively dry mouth.

It is thought that tannic acid (TA) might mucks with this process thus often leaving the feeling of dry mouth after drinking some red wines. Specifically, TA might inhibit the calcium-activated transport channels that allow for diffusion of the necessary compounds needed to create the final saliva, resulting in decreased saliva production and observed dry mouth.

This theory of TA messing with the fluid and compound transport in the salivary glands that normally produce regular saliva is what the study presented today aimed to either provide support for or refute.

Brief Methods

In a nutshell, the salivary glands were removed from mice and subjected to a battery of tests involving the effect of TA of different beverages on the ability of those glands to produce saliva.

For the control, salivation was induced by perfusing the glands with cholinergic agonist carbachol for 10 mintes.

For the different beverage treatments, the salivary glands were first perfused with the beverages and then 5 minutes later perfused with the cholinergic agonist carbachol in an attempt to trigger salivation.

The total amount of saliva produced as well as the flow rate was calculated for each treatment and the control.

Calcium signaling analyses were also performed.

The beverages that were tested were: green tea, oolong tea, coffee, red wine, and white wine. The alcohol was removed from the wine samples prior to use. TA concentrations in each beverage were measured.

Results

• Saliva production was decreased after green tea, oolong tea, and red wine treatments.
• Saliva production was at first not affected, but over a short period of time production was greatly inhibited.
• Overall, there was a 40-65% inhibition in saliva production after green tea, oolong tea, and red wine treatments.
• There was no change in saliva production compared with the control for both white wine and coffee.
• Final TA concentrations for each beverage were:
  • Green tea: 47μM
  • Oolong tea: 34μM
  • Coffee: 33μM
  • Red wine: 56μM
  • White wine: 4.7μM
• There was no effect on calcium signaling for the first 30 seconds but over time there was a significant decrease (indicates an issue with calcium sustaining mechanisms).
• Caffeine did not induce salivation at any concentration.

Conclusions

The results of this short study indicate that yes, tannic acid does seem to play a role in decreasing saliva in the mouth. There does seem to be some sort of threshold for this relationship, however, since white wine which has a small concentration of tannic acid did not decrease saliva levels.

Interestingly, tannic acid levels alone do not appear to be the complete answer here, as it was shown that coffee did not influence saliva levels in the mouth even though oolong tea did, with both of them having the same tannic acid levels.

At first the researchers thought that perhaps the higher levels of caffeine in coffee (compared with the green and black teas) increased saliva levels, thus “cancelling out” the decrease in saliva caused by the tannic acid, however, after testing this theory, caffeine did not seem to affect saliva levels at all. More research needs to be done here, but for some beverages, tannin acid alone doesn’t seem to be the full story.

For wine, it does appear that tannic acid levels influence the amount of saliva in the mouth, with the higher tannic acid levels in the red wine decreasing saliva levels and the lower tannic acid levels in the white wine having no effect. An interesting follow up study would be to see where this tannic acid threshold lies. At what concentration does tannic acid start influencing saliva levels in the mouth? Certainly there seems to be an effect at 56μM and no effect at 4.7μM, but what about the wines that fall somewhere in between?

Finally, the mechanism for saliva decreasing with higher tannic acid levels does appear to be related to calcium signaling in the saliva glands. The researchers noticed that while nothing really changed during the first 30 seconds, there was a significant decrease in calcium signaling after this time period. This coincided with a delayed decreased in saliva production after beverage treatments.

Even if you don’t really find this study that interesting nor do you have a dry mouth condition that forces you to seek out more appropriate beverages for your own consumption, you at least now have a tiny little factoid you can bust out at parties to look smart in front of your wine-challenged friends!

Please feel free to leave your comments and questions about this study below.

Source:

Imamura, A., Nakamoto, T., Mukaibo, T., Munemasa, T., Kondo, Y., Kidokoro, M., Masaki, C., and Hosokawa, R. 2015. Effects of beverage ingredients on salivary fluid secretion with an ex vivo submandibular gland perfusion system: Tannic acid as a key component for the inhibition of saliva secretion. Open Journal of Stomatology 5: 12-18.