Key tips on hydration: Recognising signs and symptoms of mild dehydration

Fluids are continuously lost from the body. Water is lost via respiration and through the skin, renal system, and gastrointestinal tract1 and this water needs to be replaced. The daily water symptoms of mild dehydration 300x222 Key tips on hydration: Recognising signs and symptoms of mild dehydrationrequirement depends on a number of factors including the person’s diet, environment, age and activity level1. For adolescents over 14 years old and adults the European Food Safety Authority (EFSA) has given an adequate water intake of 2 L for females and 2.5 L for males2.

Dehydration occurs when the body loses more wáter than it takes in. Mild dehydration (equivalent to a 1-2%decrease in body mass) may have an effect on performance and may lead to an increased risk of adverse health outcomes3:

Physical performance: Dehydration can adversely affect exercise performance and it is estimated from research that dehydration equivalent to 2% of body mass loss is where a negative effect on endurance performance may occur4.

Cognitive performance: Acute dehydration – such as that resulting from 2 hours exercising in the heat can indeed affect mental performance. However, in situations where less severe dehydration occurs (such as when refraining from drinking for a relatively short period of time) authors have generally failed to find evidence of cognitive impairment5.

Disorders and Disease: There is strong evidence for an association between chronic systematic mild dehydration and urolithiasis, urinary tract infection, hyperglycaemia in diabetic ketoacidosis, and mitral valve prolapse. Association with constipation, hypertension, coronary heart disease, stroke, venous thromboembolism, dental disease, gallstones, and glaucoma is less strong6.


  • thirst3
  • tiredness3
  • palpitations due to an increase in heart rate7
  • increased body temperature as a result of decreased blood flow to the skin and sweating compromising thermoregulation7

Although these signs and symptoms are neither specific nor sensitive, it is important to consider whether dehydration might be the cause.

Read more about this topic and find a downloadable pdf of Key Tips on Hydration: Recognising signs and symptoms of mild dehydration

1. Panel on Dietary Reference Intakes for Electrolytes and Water (2005) Dietary reference intakes for water, potassium, sodium, chloride, and sulphate. National Academy Press: Washington DC. 2. EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. Available online: 3. Kolasa KM, Lackey CJ, Grandjean AC. Hydration and Health promotion. Nutrition Today 2009;44:190-201. 4. Cheuvront SN, Carter R, Sawka M. Fluid balance and endurance exercise performance. Curr Sports Med Rep 2003;2:202-8. 5. Szinnai G, Schachinger H, Arnaud MJ, Linder L, Keller U. Effect of water deprivation on cognitivemotor performance in healthy men and women. Am J Physiol Regul Integr Comp Physiol 2005;289(1):R275-80. 6. Manz F, Wentz A. The importance of good hydration for the prevention of chronic diseases. Nutr Rev. 2005;63:S2-S5. 7. Kavrouras SA, Anastasiou CA. Water physiology. Nutrition Today 2010;45:S27-S32