Biomarkers for Noninvasive Assessment of Human Hydration

Dehydration, or the loss of body water, is a common health problem during military operations, athletic events and illness, particularly in children and the elderly. Warfighters frequently become dehydrated when training or fighting in hot and mountainous environments because heat and high altitude increase body water losses. The negative consequences of dehydration worsen as body water losses increase. Severe dehydration (>10%) is a life-threatening emergency that may result in heat illness, seizures, permanent brain damage or death. The most common type of dehydration is caused by sweat loss during heavy physical labor or exercise (hypertonic dehydration). A different type of dehydration can be caused by blood loss, burns, diarrhea, vomiting or diuretic drugs used for example by diabetics (isotonic dehydration). Despite the critical importance of proper fluid balance to human performance and health, no field-expedient, non-invasive dehydration test is available for either form of dehydration. The ultimate goal of this project is to develop a field-expedient, non-invasive test for both types of dehydration. The test will be sensitive to 2% dehydration, a critical threshold for performance impairment and a statistically valid decision point for hydration assessment.

Design: Fifteen volunteers will be first euhydrated (well-hydrated) and then moderately dehydrated (2-4%) using two procedures. First, sweat loss during exercise in the heat without fluids (hypertonic dehydration). Second, excessive urination stimulated by a diuretic pill called Lasix (isotonic dehydration). SRP biomarkers in saliva samples will be compared to changes in body weight, and to known hydration indicators in blood and urine. Results will identify the best SRP biomarkers for diagnosing both types of dehydration and compare accuracy of the new saliva test to the existing hydration indicators.

Inclusion criteria

• Signed Informed Consent Form
• Males and females between 18-40, healthy and aerobically fit determined by VO2max test. Minimum 45 ml/kg/min for males and 40 ml/kg/min for females
• Willing to stop drinking any alcoholic beverages, taking all supplements and limit medications to those approved for the study
• No heart conditions assessed by medical history and passing the PAR-Q
• Complete and pass medical exam

Exclusion criteria

• Positive response to any PAR-Q questions
• Physical problems/injuries associated with walking or cycling
• VO2Max below 45 ml/kg/min for men and 40 ml/kg/min for women
• Allergy to sulfa drugs
• Existing heart and or lung conditions
• Pregnant or breastfeeding
• History of heat illness or heat injury
• History of kidney stones or chronic renal problems
• History of orthostatic hypotension, diabetes or gout
• Taking certain medications: NSAIDS [anti-inflammatory/pain medications], digitalis [a type of heart medication], lithium and anti-depressants [medications used in psychiatry], anti-hypertensives [medications to lower the blood pressure], anti-fungals [medications used to treat infectious type of mold], supplements or anti-cholinergic drugs)
• Taking any supplements, particularly creatine in 24 hours before the start of the study, or during the study
• Alcohol consumption 24 hours before the start of the study, or during the study
• Incapable to give informed consent
• Anemia