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Evaluating Dietary Supplements

Quick Hit Summary

There are 1000’s of nutritional supplements on the market today. Unfortunately, a portion of these are nothing more than fools gold. In order to determine if the product being peddled to you is legit or snake oil, one must know how to conduct scientific research. The first step is figuring out what the product is made of and the claims made by the manufacturer. This is the ONLY TIME you should use a search engine like google or yahoo. Upon learning the ingredients of the product, research them on pubmed.gov to see if there is any supporting evidence to back up the claims made by the manufacturer. Also, if the manufacturer provides a list of references, be sure to check out the source of them… are they coming from peer reviewed scientific research journals or general magazines and websites? Are they completed in animals or humans? Although this may seem intimidating at first, I highly encourage you to use this process when evaluating supplements. Doing so will assist you separate the gold from the fool’s gold!

Separating the Gold from the Fool’s Gold

Figure 1 Are you starting to get overwhelmed by all these miracle supplements?10

Regardless of if I’m watching TV or reading various publications, I feel as if I’m constantly bombarded with advertisements for the next great miracle supplement. Sometimes I’ll flip the page/channel without thinking much of it. Other times, the claims are so outrageous, I can’t help myself and will watch the entire advertisement. After viewing these ads, I’m shocked that we’re not all living to ripe age of 100 years while maintaining the virility and physical prowess of our 20’s!

As a consumer, it can be difficult to separate supplements with valid health and performance benefits vs. those which are worthless. In order to prevent yourself from having supplements peddled to you by a “snake oil salesman”, it’s important to critically evaluate new products.

Recently, one of my good friends asked me about a product called Gluconic® DMG (manufactured by DaVinci Laboratories of Vermont)1 that was recommended to some of her athletes by a doctor they were seeing. I had never heard of the product, so did what I do best—> I researched it! I’d like to take you along for the ride and using this product as an example, demonstrate how one should evaluate dietary supplements and claims.

Step 1: Figuring Out What the Supplement Is Made Of

The first step in researching any supplement is figuring out what ingredients are contained within the product. Not being familiar with Gluconic® DMG, I did some background searching on it via google.com. I must emphasize, the ONLY TIME I USE GOOGLE.COM (OR SIMILAR SEARCH ENGINE) TO RESEARCH A SUPPLEMENT is when I’m completely unfamiliar with the product and its supposed health/performance benefits. In other words, google.com is a good source to figure out what a product contains, and health benefits claimed by the manufacturer. However, google.com is generally useless in terms of finding out if a product is useful or supported by research as discussed in the article Why Many Supplement Forums and Retail Sites Contain Misinformation.

Doing my google search, I came across 2 URL links that I felt were pertinent; the first being the manufacturers website for Gluconic® DMG [1]. The second worthwhile URL was a PDF file put out by Davinci Laboratories of Vermont that listed the ingredients found within the supplement and references supporting its usage2. According to these sources, the only ingredient found within the supplement is N,N-dimethylglicine (DMG)2 and it supposedly supports physical performance in athletes by:

  • Assisting with oxygen utilization
  • Decreasing lactic acid build-up
  • Speeding up post-exercise recovery time

It then goes on to say:

“The evidence that DMG can enhance the performance of athletes is quite strong. The research, along with actual field evaluation, shows that DMG is beneficial to endurance athletes (runners, team sports) as well as short-timed events (weight lifters, sprinters).”2

This statement quickly caught my attention and I scrolled down the PDF until I found the reference section that listed the research supporting these claims (I strongly suggest you pull up the URL address that is listed at the end of this article and look at the PDF before continuing on with this article). In their athletic performance section, I found 14 references listed. At first glance this seemed pretty impressive. However, quality of references is of much greater importance than quantity when evaluating a product. As I quickly analyzed the reference list, I found the following information:

  • Of the 14 references, 9 were completed on animals (6 horses, 1 rats, 1 canines, 1 “animals”- type not specified). Of these 9 sources, 2 were from peer reviewed scientific journals, 3 were from non-peer reviewed journals (ie- general “trade” magazines such as The Blood Horse, etc) and 5 of the references were never published (ie- information presented at conferences/symposiums, non published research, etc).
  • 2 of the references were from non- peer reviewed sources (Gallary, Health Foods Business) and discussed the sexual enhancing properties of products containing the ingredient N,N-dimethylglicine. Does anyone besides me find it rather humorous that a company tries to legitimize its product by listing sexual enhancement articles under their Athletic Performance section?
  • 3 references were completed on athletes, 2 of which appeared in scientific journals. The remaining reference was a private report that was never published in any scientific journal article.
  • All of the references, outside of 1 (which happened to be an article discussing the sexual enhancing properties of N,N-dimethylglicine), were completed prior to 1990.

How do I interpret all of this?

My first reaction was, “Wow, that’s a lot of animal studies with minimal human studies.” However, I realize that animal studies must be completed before human studies, so I can somewhat rationalize this predominance. On the other hand, I’m also aware that the physiology of horses, canines, etc differs from that of humans. Thus, one cannot necessarily expect humans to react the same way that animals do to a given supplement/treatment. (Please refer to the article Making Sense of Furry, Fuzzy, Animal Studies for further discussion on evaluating animal studies).

My second thought was, “I’m surprised at how old these references are with respect to when published/presented.” I’m somewhat hesitant to accept the results obtained from studies completed prior to 1990 IF there hasn’t been any additional published research to support them during the past ~15 years. Am I implying that old studies are bad? Of course not; I simply realize that advances in technology have occurred during the past 20 years that enable researchers to better understand if/how supplements work in the human body. Additionally, the lack of studies on the product, with respect to athletic performance, since 1990 also sets off a second alarm… We live in a human performance driven society!!! If there was a safe, effective ingredient that could improve physical capabilities, I would think that there would have been at least a few studies done on them during the past 15 years. When individuals see supplements that support athletic ability, they immediately think of athletes. However, these same supplements are commonly used by military, police/firefighters, physical laborers, etc. With the potential to be applied to such populations, I’d tend to believe that funding for such studies would be available if the scientific community felt it would be of assistance. I’m not saying 100’s of peer reviewed studies (on active individuals), but at least 1-3 during the past 15-20 years.

To best illustrate everything I mentioned in the preceding paragraph, I’d like you to consider creatine. Many individuals believe that creatine has only been around since the early to mid 1990’s. However, the physiological role of creatine has been studied as far back as the 1930’s in Ukraine3. Furthermore, the Soviet Union (USSR) began studying creatine’s potential ergogenic (performance enhancing) role during the 1970’s and 80’s. With evidence indicating a potential ergogenic role for creatine, research boomed on it during the 1990’s. For example, if one types in the search words creatine and ergogenic at pubmed.gov, 128 peer reviewed scientific papers show up. Now lets compare that to N,N-dimethylglicine…When I type in the search terms N,N-dimethylglicine and ergogenic no results are found. If I modify the search terms and write N,N-dimethylglicine and athletes, only 3 peer reviewed articles show up at pubmed.gov. As an FYI, these searchers were completed on January 13, 2010. These results will change as more studies are published.

My third and MOST IMPORTANT THOUGHT regarding the reference list was, “I can’t believe how few peer reviewed scientific journal articles are listed in their reference section.” Of the 14 references, only 4 appeared in peer reviewed scientific journal articles. In terms of evaluating dietary supplements, peer reviewed scientific journals are the GOLD STANDARD. Before any paper is published in one of these journals, a panel of peers (ie- experts in the field such as PhD’s, etc) carefully scrutinizes the quality of the report. If the research article does not meet their standards, it will not be published. Although poor quality studies may still be published in peer reviewed journals, it’s far fewer than non-peer reviewed scientific journals or magazines. For instance, one of the references for Gluconic® DMG appeared in Gallary. Obviously, the primary purpose of articles appearing in this type of a publication is to catch the public’s eye and sell subscriptions; not present scientific data supporting the use of a product. Which publication would you probably put greater faith in: Gallary or scientific journals such as Journal of Applied Physiology and Medicine and Science in Sport and Exercise?

A few of the other references were just presented at conferences/symposiums or private reports vs. appearing in peer reviewed scientific literature. In general, I have no problem with information presented at these types of gatherings. Commonly, the latest research is presented in these settings, prior to being published in a scientific journal. As Dr. Jamie Cooper discussed in her interview (Interview With The Expert- Dr. Jamie Cooper, PhD) many months commonly pass between the completion of a research study and it actually being published in a peer reviewed scientific journal. Thus, if you want to be on the cutting edge of the science field, I would highly encourage you to attend these conferences/symposiums (for more info on attending a national conference, simply go onto a given organizations (ACSM, etc) and look under tabs/headings such as “education”).

My concern with the symposium/conference references used in the Gluconic® DMG PDF is that there’s no indication that the data presented at the conferences/symposiums was later published in peer reviewed scientific journals. For many individuals, especially researchers working in the university setting, they must publish “X” amount of papers in peer reviewed journals to maintain their positions. For those working in the private sector, there is a definite financial motivation to get their work published. Other individuals who commonly publish research articles are those completing a PhD or MS graduate program. In some instances, a journal article must be published in order earn a graduate degree. Thus, for both financial and notoriety purposes I tend to believe that those presenting at the conferences would have substantial motivation to publish any research that they presented. I wonder if the reason as to why these individuals didn’t publish anything in peer reviewed literature had to do with their scientific evidence not meeting the quality standards set by various scientific journals. I want to emphasize that the previous sentence is merely my speculation as I have no hard core evidence to back it up. Maybe I’m wrong and publication bias prevented them from being accepted (assuming something was submitted).

Despite the three aforementioned problems with regards to their references, I try to keep an open mind regarding the scientific evidence supporting the use of the product. Each one of the aforementioned caveats does not necessarily mean a product is bad. However, when all three are present, I’m simply more hesitant to accept claims made by a manufacturer.

All this being said, what should one do if they shouldn’t use google.com to determine the effectiveness of a product? I suggest using the free, peer reviewed, scientific database known as Pubmed. For a quick tutorial on how to use Pubmed, please check out my article Pubmed for Dummies.

Step 2: Researching the ingredients of Gluconic® DMG using Pubmed

Now that we’ve figured that DMG is the only ingredient present within the supplement and what its recommended uses are, Pubmed is the next destination. I first researched the specific peer reviewed journal article that was referenced in the aforementioned PDF. This study examined the effects of taking 135 mg of DMG or a placebo 5 minutes prior to a exhaustive treadmill test in endurance trained athletes (3 males, 13 females; mean age- 27)5. Each athlete completed 2 separate treadmill test (one with placebo prior to test & one with DMG prior to test). Analysis of the data obtained indicated that DMG had no effect on maximum ventilation, VO2max (oxygen uptake), heart rate or total run time. Also, at submax levels, VO2 and ratings of perceived exertion were not significantly different. WOW… I’m really shocked and actually kind of disgusted by the fact that DaVinci Laboratories of Vermont reference a study to promote its product that actually showed no benefit by taking DMG. Talk about misleading the consumer and hoping that one never actually check out their references!!! No results were found when I typed the name of their other peer reviewed reference into the Pubmed search engine6. As a result, I can’t really comment on that one at all.

After looking at the peer reviewed journal article mentioned on the PDF bulletin put out by Davinci Laboratories of Vermont, I researched DMG on Pubmed using various search terms. Overall, I had great difficulty finding any articles that related to potential ergogenic benefits of DMG outside of the previously mentioned study. To my knowledge, there has been no peer reviewed study published and posted on Pubmed which has looked at the long term effect of taking DMG with respect to athletic performance. There have been a few studies looking at the substance pangamic acid which consists of calcium gluconate and DMG7. In a study involving 16 college aged male track athletes, it was found that taking 300 mg/day of pangamic acid (vs. placebo) for 21 days had no significant effect on blood lactate or time to exhaustion while running8. In another study, participants completed 2 submax bicycle ergometer tests9. Preceding each test, individuals took 2.4 grams of pangamic acid or nothing (for control testing purposes) for 2 weeks prior to completing a cycle ergometer test. Final results indicated that taking 2.4 grams of pangamic acid had no significant effect on submax heart rate or VO2 (oxygen consumption). On the other hand, there have been some studies completed in the former Soviet Union that indicated that pangamic acid may be of benefit to endurance athletes8. However, as pointed out by Gray and Titlow, many potentially confounding variables were present within the studies, making it harder to judge the validity of their results.

It should be noted that I also could not find any peer reviewed research to support that claim that DMG, “…is beneficial to … short-timed events (weight lifters, sprinters).”2

Step 3: Interpretation of the Research

After all the research has been gathered, one must interpret and determine if there is enough evidence to support the use of a given product. Based off the sparse peer reviewed research I found on DMG, I am not convinced that it would have a significant ergogenic benefit when consumed by athletes. I’m not saying that it couldn’t be beneficial; I’m just saying that current peer reviewed research conducted on athletes does not support its use. Another factor to consider when deciding if the supplement is worth buying is the price. Considering the recommended dosage for athletic purposes (Sports Practice and Fitness 375-1000mg; Endurance Sports 1000-2500mg) and the cost of the Gluconic® DMG, which I’ll let you research on your own, this supplement can get pretty costly when taken over a long period of time2. If you’re a world class athlete, looking to gain the extra inch and money isn’t a factor, I could see where you may experiment with the supplement. However, if finances are tighter, peer reviewed research simply doesn’t justify the purchase of this product.

So what would I do if an athlete came to me claiming that Gluconic® DMG has dramatically helped their performance? I’d probably say something along the lines of, “Interesting… Most of the research I’ve seen on it does not support its use. If it were me, I probably wouldn’t pay for it, but if you feel that that it’s really helping you, go ahead and take it.” I say this as the studies I looked at indicated that pure DMG (ie- not the pangamic acid) did not pose any health risk. I feel that it’s my job to make the athlete aware of the research and give them my opinion. Ultimately though, I leave the decision to take it or not up to them; assuming that the supplement doesn’t pose any health risks or illegal in the athlete’s respective sport. Maybe there is some legitimacy to the given product if the athlete is benefiting from taking it that has yet to be captured in a formal scientific research paper. On the other hand, maybe it’s related to a placebo effect more so than the actual ingredients of the product.

Bottom Line

As I hope this article demonstrates, in order to determine if a supplement is fact or fiction, it’s important that one takes it upon themselves to do a little background check on it. Unless you’re finding out what ingredients are present within the supplement, this search should not be done on google, yahoo, etc. Rather, it should be done in peer reviewed journals such as those found at pubmed.gov.

On a final note, I’d like to dedicate this article to one of my college professors, Dr. Kelli Koltyn who taught me the importance of critically evaluating scientific literature.

Gluconic® DMG is a trademark or registered trademark of DaVinci Laboratories of Vermont.


1 Gluconic® DMG Sublingual 125 mg. DaVinci Laboratories of Vermont – maker of high quality vitamins and nutritional supplements.2009. Accessed December 13, 2009 from: http://www.davincilabs.com/vitamins_supplements/gluconic-dmg-sublingual-125-mg.php.

2 Gluconic® DMG. Technical Bulletin. DaVinci Laboratories of Vermont. Accessed December 18, 2009 from: http://www.seekinghealth.com/product_files/1161668603Gluconic%20DMG%20(DMG-TB).pdf.

3 Kalinski MI. State-sponsored research on creatine supplements and blood doping in elite Soviet sport. Perspect Biol Med. 2003 Summer;46(3):445-51.

4 Alves C, Lima RV. J Pediatr (Rio J). Dietary supplement use by adolescents.2009. Jul-Aug;85(4):287-94. Epub 2009 Jul 7.

5 Bishop PA, Smith JF, Young B. Effects of N,N-dimethylglycine on physiological response and performance in trained runners. J Sports Med Phys Fitness. 1987 Mar;27(1):53-6.

6 Pipes T. The effect of Pangamic acid on performance in trained athletes.
Med. and Sci. in Sports and Exercise. 1980; 12: 98.

7 Tonda ME, Hart LL. N,N dimethylglycine and L-carnitine as performance enhancers in athletes. Ann Pharmacother. 1992 Jul-Aug;26(7-8):935-7.

8 Gray ME, Titlow LW. The effect of pangamic acid on maximal treadmill performance. Med Sci Sports Exerc. 1982;14(6):424-7.

9 Girandola RN, Wiswell RA, Bulbulian R. Effects of pangamic acid (B-15) ingestion on metabolic response to exercise. Biochem Med. 1980 Oct;24(2):218-22.

10 Uploaded by Christine Dela Cerna. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. Accessed Jan 11, 2012 from: www.flickr.com/photos/amitbelani/199288914/

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Written on January 17, 2010 by Sean Casey
Last Updated: January 11, 2013

This information is not intended to take the place of medical advice.Please check with your health care providers prior to starting any new dietary or exercise program. CasePerformance is not responsible for the outcome of any decision made based off the information presented in this article.

About the Author: Sean Casey is a graduate of the University of Wisconsin-Madison with degrees in both Nutritional Science-Dietetics and Kinesiology-Exercise Physiology. Sean graduated academically as one of the top students in both the Nutritional Science and Kinesiology departments.
Field Experience: During college, Sean was active with the UW-Badgers Strength and Conditioning Department. He has also spent time as an intern physical preparation coach at the International Performance Institute in Bradenton, FL. He also spent time as an intern and later worked at Athletes Performance in Tempe, AZ. While at these locations he had the opportunity to train football, soccer, baseball, golf and tennis athletes. Sean is also active in the field of sports nutrition where he has consulted with a wide variety of organizations including both elite (NFL’s Jacksonville Jaguars) and amateur athletic teams. His nutrition consultation services are avalable by clicking on the Nutrition Consultation tab.