Nutrition, Podcast, Science

Evidence-based supplements for triathletes and endurance athletes | EP#193

 August 5, 2019

By  Mikael Eriksson

​Evidence-based supplements for triathletes and endurance athletes | EP#193

TTS193 - Evidence-based supplements for triathletes and endurance athletes

What dietary supplements should triathletes and endurance athletes consider using based on current evidence? We go through a recent review paper that has analysed all the current evidence to come up with clear guidelines for which supplements are potentially beneficial and which will just result in expensive pee.

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In this Episode you'll learn about:

  • Supplements used to prevent or treat nutrient deficiencies. 
  • Supplements (sports foods) used to provide a practical form of energy and nutrients. 
  • Supplements that directly improve sports performance. 
  • Supplements that improve performance indirectly. 
  • Adverse effects and anti-doping rule violations from lack of quality assurance in supplement manufacturing. 

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Background to the paper

5:25 -

  • The paper came about due to the initiative of the International Olympic Committee, specifically their medical and scientific commission. 
  • They gathered a panel of experts to discuss the place of dietary supplements as part of the nutrition and training strategy of high performance athletes. 
  • This resulted in a consensus statement that was also submitted to the British Journal of Sports Medicine, where it was accepted and published. 

Overview of the paper

6:47 -

  • The paper lists four objectives:

    1) The management of micronutrient deficiencies.
    2) The supply of convenient forms of macronutrients and energy/calories.
    3) The provision of direct benefits to performance. 
    4) Indirect benefits, such as being able to facilitate more intense training regiments, better recovery, better body composition or reduced risk of injury/illness. 
  • They then discuss how athletes are using supplements - key points to note:

    Supplement use increases with level of performance. This makes sense being they are seeking marginal gains. 

    Supplement use increases with age. Older athletes may have micronutrient deficiencies, or cannot absorb it from normal food anymore. 

    Supplement use is higher in men than woman. 
  • The review then discusses limitations and constraints of the review. 

    They have relied primarily on studies of healthy adults, and have not used studies of elite athletes of mechanistic and animal models - mechanisms were considered not necessary to demonstrate an effect meaningful to an athlete. 
  • Whenever you see animal models being used as a reason you should try something, be very careful as we don't know how this will translate to humans. 
  • They also note that an individuals habitual diet can affect gene expression and their microbiome. 

    These can effect the response to supplementation. 

    variation in genome between individuals is less than 0.01%, the variation in microbiome is significant - between 80-90%, and both these factors could affect athletic performance. 

    This explains why it may be different to get significant results in some studies, and would ideally need to be controlled for. 

Supplements used to prevent or treat nutrient deficiencies


  • When there is a deficiency in a nutrient or micronutrient it can lead to measurable impairment in your performance.

    This happens either directly or indirectly - e.g. by reducing your ability to train well (e.g. iron deficiency), or to stay free from illness or injury (e.g. vitamin D). 
  • For supplements to be a viable strategy, it's important that the athlete has a diagnosed sub-optimal nutritional status with regard to the nutrients. 

    If that's the case, supplements may be part of the overall treatment plan. 
  • The complete assessment of the athlete should include a detailed medical and nutritional history, an evaluation of current diet and anthropometrical measures and body composition, as well as biochemical testing. 
  • Nutrients that often need to be supplemented under these circumstances are iron, calcium and vitamin D (seen in table 1 of the paper).

    Iodine may also be needed for those living in areas with low levels of this in food, or not using iodized salt. 

    Folate can be necessary for women who become pregnant. 

    Vitamin B12 is often needed for those following a vegan, or near vegan diet.

Vitamin D deficiency

  • This deficiency affects many body systems, and many athletes and people in general are at risk of this deficiency at different times during the year because most comes from skin exposure to sunlight. 
  • For example, Finland is a dark place for a lot of the year so Finnish residents are advised to supplement with vitamin D year round, or at least through the winter months. 
  • My personal recommendation would be if you're living in a climate where at parts of the year you don't get much exposure to direct sunlight, then it makes sense to supplement with vitamin D. 
  • Deficiencies can make you get ill more easily or get tired, but they can be treated easily with supplements. 
  • Things like suncream or arm warmers can also affect your exposure and absorption of vitamin which should be considered. 

Iron deficiency

  • Sub-optimal iron status may result from a limited iron intake in the diet. For this reason it's more common in vegetarians and vegans.
  • It could also come from poor absorption of food iron, and an inadequate energy take in general. 
  • You may also have an increased need in certain periods of your life, or a more general increased need - e.g. menstrual blood loss, or altitude training increase your need for iron. 
  • Doing a lot of running can increase your need for iron due to foot strike haemolysis. 
  • Iron is something you want to ensure you have a diagnosed deficiency before you attempt supplementation, as it can be toxic in certain doses. 
  • It has been shown that if you have an iron deficiency and you start supplementation it works well and you lose the fatigue and anaemic, and your blood can carry more oxygen. 

Calcium deficiency

  • Particularly relevant for athlete who limit their dairy intake as you may be at risk for calcium deficiency. 
  • Also if you're restricting your energy intake in general or have experienced disordered eating, these factors increase your risk of sub-optimal calcium status. 
  • Calcium is important for bone health. 
  • If you have a calcium deficiency you may need supplementation to restore bone health, but you should first check if you do have a diagnosed deficiency. 

Supplements used to provide a practical form of energy and nutrients

18:57 -

  • This includes things like sports drinks, gels, bloks, electrolyte replacement, protein supplementation etc. 

    Things that give you easy access to certain nutrients or energy that you may not get enough of otherwise. 
  • Sports drinks can be used to provide carbohydrates, as well as sodium and some electrolytes. 

    This is supported as something that can be used during exercise, and post-exercise for rehydration and refuelling. 
  • Energy drinks (e.g. Red Bull) can be used to provide carbohydrate but also caffeine and other ingredients. 

    This is supported as an alternative during exercise, and could be used as a pre-exercise caffeine supplement. 
  • Sports gel, or similar (e.g. bloks) are recommended as a way to get in carbohydrate during extended or intense exercise. 
  • Electrolyte replacement supplements (e.g. drinks with mostly electrolyte not carbs) are recommended for rapid rehydration following dehydration during exercise. 

    They can also be used for replacement of large sodium losses during endurance activities. 

    For more information on these drinks check out: ​Hydration in endurance sports: a Q&A with Andy Blow | EP#191​​​
  • Protein supplementation (e.g. powders, ready to drink liquids and bars) are recommended as post-exercise recovery following key training sessions or events where adaptation requiring protein synthesis is desired. 

    They are also recommended for achievement of increase in lean mass - but this is more for resistance training and strength and power athletes. 
  • If you're doing hard, or long sessions where protein synthesis will be a key part of recovery and adaptation, then protein supplementation can be helpful. 
  • Liquid meal supplements, which contain 15-20% protein and 50-70% carbohydrate, can be recommended to supplement diet with high energy demands. 

    It can also be recommended as a low bulk meal replacement, for example pre-event. 

    Also potentially as post-exercise recovery as you're getting your carbohydrate and protein. 
  • Bars which typically include 40-50g carbohydrate, and 5-10g protein, usually low in fat and fibre are recommended as a potential carb source during exercise. 

    They are also recommended as post-exercise recover, particularly when they provide enough protein. 
  • Finally, protein enhanced food is recommended - e.g. milk, yoghurt, ice cream, cereal bars, and other food forms that have added protein. 

    These are listed as value added food able to achieve protein target for post-exercise use, or to improve protein content of other meals and snacks in the athletes diet. 

Key point

  • This paper is not recommending you use all of these things and rely upon them daily, but there may be a time and a place for one or a few of these things.

    Even though they discuss supplements, they key point is that they can be useful, but not if you use them instead of less healthy food. 

    The idea is to use as little supplements as possible, only when there is a need to use supplements. 
  • For endurance athletes we need to get in energy or it's impossible to stay in caloric balance, so there are good reasons to use supplements, but not necessarily as a normal afternoon snack! 

Supplements that directly improve sports performance

25:35 - 

  • There are a few supplements with good to strong evidence for achieving performance in specific scenarios. 

    For triathletes there are two: caffeine and nitrate.
  • For endurance athletes competing in short events - 10 minutes or less - there are two more that can be useful: beta alanine, and sodium bicarbonate. 
  • There is one more supplement that generally has a lot of benefits for athletes: creatine. 

    However, these benefits are mostly related to strength and power. 


  • Caffeine is the most studies and has the best evidence for endurance athletes. 
  • Caffeine is a stimulant that has well established benefits for athletic performance across endurance based situations. 

    It also has benefits on short-term, supramaximal or repeated sprint tasks. 
  • The protocol of use for caffeine is to take 3-6mg/kg body weight, 60 minutes before exercise or racing. 
  • During exercise and racing, you can take lower doses (less than 3mg/kg) which is recommended to be consumed with a carbohydrate source.
  • Caffeine has been shown to increase time to exhaustion, and has improved time trial activities of varying durations from 5-150 minutes across numerous exercise modalities. 
  • The range of impact has varied quite a bit and is not specifically listed.
  • It is stated that lower doses of caffeine - 150-300mg - consumed during endurance exercises after 15-18 minutes of activity may enhance cycling time trial performance by 3-7%.
  • Usually it is the case that more advanced athletes have lesser benefits than less advanced athletes. 
  • Larger doses of caffeine - more than 9mg/kg bodyweight do not appear to increase the performance benefit and are more likely to increase the risk of negative side effects.

    These include nausea, anxiety, insomnia and restlessness. 
  • If you do consume caffeine during activity it should be done concurrently with a carbohydrate source for improved efficacy. 
  • As with any supplement you're going to take during racing, you need to practice it in training to discover what the optimal timing and amount is for you specifically. 
  • ​To give some real world examples of caffeine amounts:

    In a brewed cup of coffee there is on average 95mg of caffeine, which is quite a low dose for somebody at 60kg (it would be 1.5mg/kg bodyweight). The range is 70-200mg though as it depends a lot on the roast. 

    In decaf coffee there is 2-3mg on average. 

    In a shot of espresso there is on average 63mg - which would be bodyweight for a 60kg athlete. 

    In a cup of instant coffee there is somewhere between 65-85g of caffeine. 

    In a single shot latte there is between 47-75mg of caffeine. 
  • If you're considering caffeine supplementation, coffee is not the way to get caffeine, you need to go for specific products. 
  • Personally I use Science in Sport caffeine shots, which contain 150mg of caffeine. 

    I weigh around 70kg so this would be just under 3mg/kg bodyweight, so it's still on the low side of things! 

    For me, two shots would be a bit more than bodyweight so that might be just right for me! 


  • There's a lot of evidence for creatine, and it is great, BUT this is for power and strength athletes mostly. 
  • I checked the paper to see if there was a use case for endurance athletes but there doesn't seem to be. 
  • If you're a strength athlete and endurance athlete and interested in bigger gains, it may be worth looking into creatine more.
  • It's one of a few supplements that does work and has a proven evidence base for it. 


  • Nitrate is found in foods such a beetroot. 
  • In the recent decade it has been researcher more and we are starting to see the evidence grow that it can be a helpful and beneficial supplement for endurance performance. 
  • The protocol in the paper is to supplement with 310-560mg 2-3 hours before activity. 

    Also prolonged periods of supplementation appear beneficial to performance, especially in highly trained athletes where performance gains from nitrate supplementation appear harder to gain. 
  • Supplementation with nitrate has been associated with improvements of 4-25% improvement in time to exhaustion. 
  • Time to exhaustion is not as good or as rigorous a test as a pure time trial as there's a lot of variability and psychological factors. 

    Time trial performance assessments are the gold standard. 
  • Looking at time trial specific improvements the range is 1-3%. 
  • Referring back to the Andy Jones episode, he was conservative but he talked about typical performance benefits of 1%, but he does work with a lot of elite athletes. 
  • There are a few side effects of nitrate that may cause some limitations: 

    Some athletes are susceptible to GI upset as a result of nitrate supplementation, so it should be tested in training prior to using it in racing.

    As with caffeine, there appears to be an upper limit to the benefits of consumption - more is not always better. Going from 500mg to 1000mg, performance improvements don't change.

    Performance gains are harder to achieve in highly trained athletes. 
  • If you are going to supplement from nitrate, I would say make sure you are getting nitrate in the right amount. 

    Just buying beetroot juice from the grocery store isn't great because the variation in nitrate concentration is massive. 

    There's a paper called: What's in Your Beet Juice? Nitrate and Nitrite Content of Beet Juice Products Marketed to Athletes which shows that even in products marketed specifically to athletes, the variation is massive. 
  • One good product that was discussed in the Andy Jones episode is called Beet It - it's the one I use and contains 400mg per shot of nitrate which is right in the sweet spot of what you need. 

Beta Alanine

  • Beta Alanine augments intracellular buffering capacity, having potential beneficial effects on sustained high intensity exercise performance. 
  • For triathlon purposes, this doesn't seem that beneficial as it has effects on durations of 30 seconds - 10 minutes. 

    If this is interesting to you, have a look at the paper and particularly table number three. 
  • There is the argument that if you do high intensity exercise you may want to supplement specifically for that exercise to do slightly better in training and possibly get better adaptations. 

    However, I don't think it's something that's ever been proved to work, and you could equally supplement with something like caffeine for this purpose too. 
  • I think triathletes and coaches would be using this more if it was particularly beneficial in triathlon, but we know they're not at present. 

Sodium bicarbonate

  • The same applies as above with beta alanine. It's beneficial for short durations so not as relevant to triathlon. 
  • It's similar to beta alanine in that it increase buffering capacity, but it's extracellular rather than intracellular. 

Supplements that improve performance indirectly

42:19 - 

  • There are a lot of supplements that claim to enhance performance indirectly by supporting athletes health, body composition and ability to train hard and recover quickly, adapt better, tolerate pain etc. 
  • Reviews have noted that there's a low quality in studies that support these supplements that claim to support immunity for example. 

    These issues are things like small sample sizes, poor controls and unclear procedures for randomisation. 

    Therefore, there are not many supplements that have actually been shown to be beneficial indirectly. 
  • In the paper, these are in table four, five and six. 

Supplements for immune support

  • These are in table four in the paper. 
  • The review notes that the most promising candidates to assist in the prevention or treatment of immune function, particularly upper respiratory symptoms, are vitamin D and probiotics. 
  • Vitamin C may be beneficial for prevention during periods of heavy exertion. 
  • Zinc may be beneficial at the onset of symptoms. 
  • Probiotics have the additional benefit of reducing the incidence of travellers diarrhoea and gastrointestinal infection. 
  • The evidence for efficacy of vitamin D and probiotics is moderate. The outcome measure used is preventing or treating upper respiratory symptoms. 
  • Vitamin C has moderate support for preventing upper respiratory symptoms, but no support for actually treating it. 
  • Zinc has no support for prevention, but has moderate support for treating upper respiratory symptoms IF you start the consumption within less than 24 hours of the symptom onset. 
  • There is a long list of things that have low support, including bovine colostrum, polyphenols. 
  • Those with limited support include glutamine, caffeine, echinacea, omega-3. 
  • Finally in no support they mention vitamin E and beta glucan, 

Supplements to assist training harder, faster recovery and injury prevention/accelerated return

  • These are in table five in the paper. 
  • The supplements that look like they have the most positive effects for endurance athletes are vitamin D and certain anti-inflammatory supplements. 
  • Vitamin D has pretty good evidence for enhanced adaptive response to stressful exercise. 

    If you are deficient in vitamin D you may also be a greater risk of stress fractures, so supplementation may reduce this risk. 
  • Anti-inflammatories, such as curcumine (found in tumeric), has some evidence supporting it for decreasing inflammation and indirect markers of muscle damage.
  • Another supplement with proven anti-inflammatory benefits is tart cherry juice. 
  • Anti-inflammatory effects may be beneficial but it really depends on the context. 

    It may also blunt the adaptive response to exercise, especially if these supplements are consumed immediately after training so it may be better to wait a while. 
  • It's difficult to say whether having less inflammatory markers is actually a good thing. 
  • Personally I don't use anti-inflammatory supplements, and I'm not really tempted to start after reading this review. 
  • Beta hydroxy beta methylbutyrate is also noted as the benefits are indirect but seem more promising for strength and power athletes rather than endurance athletes. 
  • Omega-3 supplements and creatine have some indirect benefits for certain athletes, but again not that relevant for endurance athletes. 

Supplements to promote and assist gaining lean muscle mass, or loss of body fat mass

  • Protein has consistently been found as something that can increase lean muscle mass. 

    For some triathletes and endurance athletes may need to work on this, particularly those from a running background who are really lean and may need to bulk up a little. 

    This does need to be combined with some resistance training, not letting all the endurance training tear down the potential effects of the muscle gains you're looking for. 
  • Leucine is listed but doesn't have any efficacy evidence that's really reliable so far. 
  • When it comes to losing fat mass, none of the things listed in the article seem to have an effect other than protein. 

    These include omega-3 and green tea.
  • Protein can have a small but significant effect of losing fat mass when you supplement with that. 


52:04 - 

  • For direct benefits for triathletes you have caffeine and nitrate. 
  • For indirect benefits relating to keeping healthy, you've got vitamin D and probiotics to reduce the risk of upper respiratory symptoms. 

    For keeping healthy in terms of injuries, you have vitamin D to reduce the risk of stress fractures, and anti-inflammatory supplements to recover better. 
  • If you want to improve your lean muscle mass, protein is a good one. 
  • Some supplements that are worth taking if you have a proven deficiency are vitamin D, iron and calcium. 
  • There are a large number of things recommended to provide practical energy when needed. 

    When you're training for example, or finishing a session, sports nutrition products like sports drinks, gels, bloks, protein sports bars ect can be used. 

Adverse effects

51:33 - 

  • The review paper does note that the use of supplements may cause adverse effects and the safety and composition of the product may not be optimal. 
  • The patterns of use by athletes may also be inappropriate. 

    Poor practice by athletes includes things like indiscriminate mixing and matching of many products without regard to total dosage of some ingredients or problematic interactions between ingredients. 
  • Keep in mind that supplements are regulated like food ingredients, not pharmaceuticals, so the regulations are much less stringent. 

    This means there are not the same requirement to prove benefits, or show safety with acute or chronic administration.

    There's also no strict quality assurance requirements and liberal labelling may be used. 
  • The Food and Drug Administration (FDA) in the USA have recently recalled supplement products that contain excessive doses of vitamin A, D, B6 and selenium because of potentially toxic levels of these components. 
  • In the USA in 2015, approximately 23,000 emergency department visits annually were reported to be associated with dietary supplement use. 

    This isn't necessarily big or small, but just to note that there is a certain risk associated with supplements. 

Anti-doping rule violations

56:00 - 

  • This is relevant for all age-groupers and professional athletes, particularly faster age-groupers. 
  • Many athletes consider supplements to be safe, and there can be some discrepancies in the list of prohibited substances on the WADA website, and what they are called on supplement labels. 

    This can make it difficult to recognise whether you are consuming a prohibited substance.
  • Most concerningly, there is a real risk that a supplement may contain a prohibited substance as an undeclared ingredient or a contaminant. 
  • This study: Australian Supplements Survey Highlights Need for Testing reported that 15% of more than 600 supplement products contained undeclared banned substances. 
  • These banned substances have been found in very common supplements such as vitamin C and multivitamins and minerals. 

    This is rare compared to a pre-workout supplement for example, but it's worth keeping in mind. 
  • There are efforts being made to address these problems, which include the use of third party auditing activities to identify products that athletes may consider to be at low risk of containing prohibited substances. 

    They're not an absolute guarantee but it's the best we currently have. 
  • One of the authorities that does this third party testing is ​Informed-Sport

    This is a global quality assurance programme for sports nutrition products. 

    This programme certifies a product not just once, but every batch of it, and the raw materials used in it. 
  • Personally I made sure that all the supplements I use are on the Informed-Sport list of trusted brands. 
  • These include:

    - Science in Sport for things like gels, sports, drinks and caffeine shots. 
    - Precision Hydration for electrolyte products. 
    - Beet It for nitrate. 
    - Bulk Powders for whey protein. 

Final thoughts

  • Using supplements should not be compensating for a poor diet or poor nutritional choices. 
  • Use of supplements by young athletes is discouraged except when full evaluation of nutritional status suggests it is warranted. 

Links, resources and contact

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