Could Urinary Tartaric Acid Levels Function as a Proxy for Self-Reported Wine Consumption Habits?

One of the major disadvantages to using self-reported alcohol consumption patterns in research studies is that fact that self-reported data may not actually reflect the true nature of individual alcohol consumption rates.  For example, some people may be hesitant to report the actual amount of alcohol they consume based on negative social stigmas.  Additionally, misunderstandings regarding the true size of a glass of wine may result in inaccurate self-reported data, as some people’s “one glass of wine” might be a lot more than the 5oz standard glass of wine outlined by the Center for Disease Control and Prevention (US).

Finding a biomarker than can be easily measured from blood or urine has been examined in a few clinical and epidemiological studies, and may be very useful as a more accurate representation of alcohol consumption rather than relying on self-reported data which as we’ve seen before is highly variable with

Photo by József Rippl-Rónai [Public domain], via Wikimedia Commons

Photo by József Rippl-Rónai [Public domain], via Wikimedia Commons

significant limitations (see a related study with mixed results reviewed in 2012 by The Academic Wino by clicking here).

Previous studies have examined total urinary resveratrol metabolites as possible biomarkers for wine consumption, though it has been shown to be highly variable and likely ill-suited for this sort of measure.  First, resveratrol levels are highly variable between red and white wines, so measuring resveratrol metabolites in urine would highly underestimate wine consumption levels for those individuals that drink primarily white wines or drink a combination of red and white wines.  Second, resveratrol levels are known to be highly variable between grape varieties and also from one winemaking technique to the next, so depending upon what type of wine was consumed and how it was made the levels of resveratrol metabolites in urine will be widely variable.

As a result of this variability, the need for a different biomarker to represent wine consumption is required, and that is where the study presented today comes into play.

One possible option for such a biomarker, according to some preliminary studies, is tartaric acid.  Tartaric acid makes up a significant portion of wines, falling between 1.5-4.0g/L.  It occurs naturally in grapes, and is virtually absent or negligible from most other plant species.  The only fruit that has tartaric acid levels comparable to grapes and wine is the tamarind, a sour fruit consumed mostly in tropical locations, which likely isn’t being consumed in most other regions around the world.

This unique-to-grapes characteristic makes it highly desirable as a possible biomarker, as if tartaric acid is present in one’s urine, logic would suggest that grapes or wine were likely consumed by that particular person.

Another benefit of using tartaric acid as a biomarker of wine consumption is that it does not degrade during the winemaking process, and its levels in red and white wines are relatively constant.

Photo By Benjah-bmm27 and Jynto (Derivative of public domain file from Commons.) [Public domain], via Wikimedia Commons

Tartaric Acid.   Photo By Benjah-bmm27 and Jynto (Derivative of public domain file from Commons.) [Public domain], via Wikimedia Commons

A few preliminary studies have found some promising finding regarding the use of tartaric acid as a biomarker for estimating wine consumption.  Specifically, one study in grape juice found that urinary tartaric acid levels significantly increased after grape juice consumption, and one in wine found that urinary tartaric acid levels were significantly higher in wine consumers than in non-wine consumers.

The study presented today aimed to build on this preliminary knowledge and to examine the use of tartaric acid as a biomarker for wine consumption.

Methods

The wines used in this study were 85% Tempranillo, and 15% Graciano and Granacha Tinta from the 2009 vintage (Rioja, Spain). All wines were made in the same batch on the same day, and had a pH of 3.7 and alcohol level of 13%v/v.  The tartaric acid level in the experimental wines was 1737 +/- 17 mg/L.

A total of 21 subjects participated in this study, all Caucasian men between the ages of 21 and 50 (mean = 30.7 +/- 5.9 years).  Average BMI for the group was 24.7 +/- 2.7 kg/m2.

**Authors note:  only men were considered for this study due to possible variability in women due to individual menstrual cycles.

For 7 days prior to experimentation, participants were asked to do a “washout”, where they were instructed to avoid and wine or grape products.

On the morning of the experiment, urine samples were collected.

For the actual experiment, participants were asked to eat dinner and drink a randomly assigned amount of the red wine: 100mL, 200mL, or 300mL.

Urine samples were collected every morning following experimental wine consumption.

Tartaric acid levels were measured in all urine samples.

Results

  • Estimated levels of tartaric acid intake were 174mg for the 100mL wine group, 347mg for the 200mL wine group, and 521mg for the 200mL wine group.
  • Prior to experimentation, very low levels of tartaric acid were found in participants’ urine, indicating possible influence from individual diets.
  • After consuming the different amounts of wine, tartaric acid levels in urine of the participants increased 27-fold for the 100mL wine group, 52-fold for the 200mL wine group, and 80-fold for the 300mL wine group.
  • There was a significant direct association between the amount of wine consumed and the tartaric acid levels in the urine of participants.

Conclusions

The overall results of this study were very straightforward—drink wine? Increase urinary tartaric acid levels.  Drink more wine?  Increase urinary tartaric acid levels even more.  Drink EVEN MORE wine?  Increase urinary tartaric acid levels much much more.  Basically, the more wine one drinks, the higher the tartaric acid levels in the urine becomes.

This sounds like pretty solid support for using tartaric acid as a biomarker for estimated wine consumption levels, however, the limitations of the study render the results not applicable to any other group other than Caucasian males between the ages of 21 and 50.  To me, these results provide support in a concept-of-theory style analysis, though due to the small sample size and homogeneity of the study subjects, I would be hesitant to shout from the mountain tops that we should all adopt tartaric acid as the new standard marker for wine consumption levels in humans.

First, the overall sample size of this study was relatively small.  21 subjects is not a very large number of participants, though the extremely strong correlation (r-squared value = 0.9220; p<0.001 -> very strong and significant correlation) between wine consumption levels and tartaric acid levels the urine makes me think that the results may have some merit and is promising.

Second, all of the participants in this study were male.  The authors assumed using females would produce much more highly variable results due to the physiological changes associated with the menstrual cycle and possible interference with tartaric acid levels in the urine.  As a result, there’s no way of telling if using tartaric acid as a biomarker for wine consumption would be appropriate for female wine consumers or not.  I’m somewhat surprised of the omission, as the study was simple enough that I would imagine getting a small cohort of women to at least test these predictions would be pretty easy.  Maybe tartaric acid levels in urine would be more variable in women, but maybe not.  Perhaps the correlation would still be significant regardless of this possible variability.  There is no way to know without testing it, and since

Photo By Frank Kovalchek from Anchorage, Alaska, USA (Tiles showing a wine drinker in Seville, Spain) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Photo By Frank Kovalchek from Anchorage, Alaska, USA (Tiles showing a wine drinker in Seville, Spain) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

women make up a huge chunk of the wine consumer demographic, it would be a valuable thing to test.  My only guess is that the authors only had a small amount of funding to work with, so they had to optimize experimental conditions as much as possible with few resources (as a researcher, I have been there!)

Finally, while using tartaric acid as a biomarker for wine consumption levels may be useful in an “immediate” or “current” situation, it likely would not be appropriate for long-term usage information.  After 7 days of not having any wine or grape products, participants in this study significantly reduced their tartaric acid levels.  In theory, if one consumed wine on a more regular basis in the past but then significantly reduced or stop wine intake, then tartaric acid levels would eventually drop with past consumption information relying once again on self-reported data and not a simple urine test.

Of course, I don’t believe the authors were trying to find a “be all end all” marker for wine consumption, though if these results translate into other groups as well (i.e. women, different races, etc), there is a potential for its use as an indicator for wine consumption levels in current time.

Fascinating possible application for research purposes—we’ll have to wait and see how this develops.

What do you all think of this study and possible implications for the results?  Is there anything else you would have liked to have seen tested that I did not mention in my conclusions?  Any and all comments are welcome! Cheers!

Source: Regueiro, J., Vallverdú-Queralt, A., Simal-Gándara, J., Estruch, R., and Lamuela-Raventós, R.M. 2014. Using tartaric acid as a potential biomarker for the dietary assessment of moderate wine consumption: a randomized controlled trial. British Journal of Nutrition. Published online ahead of print. DOI: 10.1017/S0007114513004108. 

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