- Carl Heneghan, clinical reader in evidence based medicine,
- Peter Gill, DPhil candidate,
- Braden O’Neill, DPhil candidate ,
- Dan Lasserson, clinical lecturer ,
- Miriam Thake, visiting research assistant,
- Matthew Thompson, clinical reader ,
- Jeremy Howick, research fellow
- 1Centre for Evidence-Based Medicine, Department of Primary Care Health Sciences, University of Oxford, Oxford OX1 2ET, UK
- Correspondence to: C Heneghan
There is no doubt that sport and exercise are beneficial for health and wellbeing. Yet, one might be fooled into thinking it is more important to heed correct nutrition and hydration advice than to actually exercise. In our analysis of the evidence of sports products1 there were six claims that were so pertinent in terms of performance that we wanted to answer them with evidence. To find the evidence we searched PubMed Clinical Queries using systematic reviews and randomised controlled trial filters.
In terms of hydration we wanted to know if the colour of urine accurately reflects hydration and whether you should hydrate before exercise or just when you feel thirsty? For nutrition, we wanted to know whether carbohydrate-protein combinations and branched chain amino acids improve performance or recovery after exercise. Finally, we wanted to determine the benefits of caffeine ingestion and analyse whether wearing compression garments helps improve overall performance?
The colour of urine accurately reflects hydration
The qualitative measure of urine colour is viewed as a simple way to assess hydration status. Athletes are advised to “observe urine output over the course of a day and notice changes in urine flow and colour. Output volume and frequency should be consistent and the colour should be getting lighter towards the end of the day, aiming for the last outputs of the day being close to clear.”2 But recommendations from the American College of Sports Medicine state that urine colour is often subjective and might be confounded.3 Many companies also provide a “urine colour chart” allowing athletes to quantify their level of hydration.4 5
Science behind the claim
Antidiuretic hormone is secreted by the posterior pituitary gland as a result of dehydration, resulting in increased water absorption in the collecting ducts …