Dietary Supplements: Potential Benefits and Risks to Athletic Performance

In the world of professional and recreational sport today the prevalence of supplementation in a bid to enhance performance is widespread and estimated to be at between 57-94% of athletes (Ronsen et al. 1999). In one study (Lazie et al. 2009), 75% of the 912 athletes analysed used at least one dietary supplementation product. The most common of those used were multivitamins, taken by over half of the subjects. However, in an eight month study conducted some time before that of Lazie’s it was found that although vitamin and mineral supplementation increased blood vitamin levels, no specific performance benefits were evident (Telford et al. 1992). Many claim their reasoning behind taking multivitamins is as a ‘safety net’ to ensure adequate levels of each micronutrient in the body, however research has shown that if one has a healthy and balanced diet they will already receive plenty of these nutrients (Rodriguez at al. 2009). It should also be stated that in the case of a poor diet with little fresh fruit or vegetables, multivitamin supplements should not replace the role of food, this may give an athlete a false sense of security and lead to detrimental health effects.

Unpublished research from Depiesse revealed the reasons given by athletes for their ingestion of dietary supplements:

•          To aid recovery from training
•          Prevent or treat illness
•          For general health
•          Performance improvement
•          Compensate for poor diet

Of course many dietary supplements on the commercial market today do have their evident ergogenic benefits, the first of which can be seen in the various forms of protein supplements such as shakes, bars and snacks. These products are easily accessible for the professional and recreational market alike and provide a convenient means of ensuring that adequate protein is ingested following a bout of exercise. Skeletal muscle synthesis is stimulated through exercise (Biolo et al. 1995) and protein feeding (Rennie et al. 1982), this effect can be enhanced by the consumption of protein following activity to promote a positive net protein balance within the skeletal muscle (Moore et al. 2009). Muscle protein synthesis is specifically maximised by the intake of 20g of high quality protein (Moore et al. 2009), intake below 20g results in sub optimal rates of muscle protein synthesis whereas intake above leads to irreversible amino acid oxidation. However, this is often the case, with many individuals overcompensating their protein intake which only requires the excretion of its nitrogen component. For the active elderly population a higher dose of post exercise protein is beneficial as they are more receptive to protein than younger exercisers. Although there is no metabolic window for this enhancement of muscle protein synthesis, it may be of benefit to eat within half an hour of a workout in order to replenish other physiological stores such as glycogen.

Another popular supplement, especially among strength and power athletes is creatine. Having been proven to improve power, strength and intermittent sprint performance through the stimulation of muscle anabolism following resistance exercise. The net result of which is muscle hypertrophy alongside increases in free creatine and phosphorylcreatine content. With regards to endurance exercise, nitrate supplementation has provided promising and significant results in reducing oxygen consumption during submaximal exercise and the ATP cost of muscular contraction.

Supplementation may also be of benefit to particular populations, especially female athletes involved in endurance sports or on a reduced calorie diet due to participation in aesthetic sports such as gymnastics. Poor nutrition alongside intense training, low body fat and weight loss can blunt oestrogen synthesis by peripheral fat. It is the effect of this, coupled with hormonal alterations that results in exercise related amenorrhea.

Many of these supplements can however result in the unintentional ingestion of banned substances (Geyer et al. 2004) as a result of contamination or poor labelling (Baylis et al). Not only can such an event lead to lifetime ban from sport but also potentially life threatening adverse effects to health.
It has also been observed that herbal supplements such as ginseng, guarna and non-herbal products including zinc and chromium can lead to detrimental health effects.

It is fair to state that the use of dietary supplements is extensive among the sporting population, this is at both a professional and recreational level. However, these individuals should be made aware that few supplements can match there extravagant ergogenic claims and should also never be used to compensate for a poor diet. This also highlights the need for the education of coaches and instructors as it has been found they pose the most influence on an athlete’s dietary habits. Lastly, the risk of obtaining a positive doping test as a result of poor supplement labelling or contamination is very much real and so these risks should be balanced against the potentials benefits before ingestion.