Dehydration 101

Mar 22, 2018

 Editor's Note: This post is authored by Beth Conlon, PhD, MS RDN, a Visiting Professor at College of Saint Elizabeth.


The recommended daily AI is approximately 5 of these 26-oz water bottles for males and 3.5 for females. Photo by Ashley Grimes.


You were on a workout roll, achieving your exercise goals several weeks in a row. Everything was going great and then – seemingly out of nowhere – symptoms that may have included fatigue, muscle aches, cramps, headaches, irritability, lightheadedness, thirst, and general malaise erupted. Your performance decreased and you started missing some of your goals. You wonder what happened? What is wrong with me?


Before hitting the internet in search of a potential rare or serious disease to blame, take a deep breath and consider your fluid intake (good news: it may be a simple fix!). Dehydration is a common occurrence among recreational gym goers and competitive athletes alike. While risk factors for dehydration1 include heat, humidity, exercising outdoors, being an older adult or infant/young child, or having a chronic illness, dehydration can happen to anyone at anytime. When dehydration hits, the physiological and performance consequences can be alarming.


What is Dehydration?

Dehydration is defined by the Mayo Clinic as occurring “when you use or lose more fluid than you take in, and your body doesn’t have enough water and other fluids to carry out its normal functions.” It can occur with as little as a 1% loss of body weight (for a 150-lb person, this translates to a 1.5 lb loss of body weight), with increased risk in heat.2 Risk of electrolyte loss through sweat also increases with heat and exercise duration. More than 1% loss of body weight can seriously hinder performance. 2 As noted by Sean Craig, when dehydrated, people often opt for a sports beverage to address fluid and electrolyte imbalances. However, many sports drinks contain added sugars and excess calories. Ensuring that you are meeting your daily water needs coupled with electrolyte replacement as appropriate is a healthy solution for short-term recovery and long-term maintenance of adequate hydration.


Daily Fluid Recommendations

How much H20 do you need daily? A rule of thumb tends to be a minimum of eight 8-ounce cups of water per day.2 But this level meets the needs of a sedentary adult. Daily fluid needs vary by individual factors such as sex, age, body size, physical activity levels, and climate (e.g., hot/humid vs. temperate or cold). The Adequate Intake (AI) established by the National Academies of Sciences, Engineering, and Medicine is a better reference point for daily fluid needs.

The AI for water is:2,3

  • 128 ounces/day in adult men (about 16 cups/day)
  • 96 ounces/day in adult women (about 12 cups/day)

These values include fluid consumed from water and other beverages (about 80% of fluid intake), and food (about 20% of fluid intake).2 You may require more than the AI on days when you exercise.


To stay hydrated, be sure to drink plenty of fluids before, during, and after activities. In addition to achieving the AI, drink an additional 24 ounces (0.75 liters) of water or fluid (sodium chloride/electrolytes) for every pound of body weight loss during exercise. Grab a drink of water before thirst hits, because by that point, you are likely already dehydrated. Also keep in mind that proper nutrition is also critical for health and work out/exercise performance.

Beth Conlon, PhD, MS RDN, is a Visiting Assistant Professor at College of Saint Elizabeth. She has a PhD in Clinical Investigation, Biomedical Sciences program, from the Albert Einstein College of Medicine. She is passionate about developing and implementing behavioral-based nutrition education programs to promote chronic disease prevention and management, reduce health disparities, and strengthen evidence-based nutrition practice. Views expressed are my own and do not necessarily reflect the official policy or position of any other agency, organization, employer, or company.





1. Mayo Clinic. Dehydration. Mayo Clinic website. Accessed March 21, 2018.

2. Murray B. Fluid, Electrolytes, and Exercise. In: Dunform M. Sports Nutrition: A Practice Manual for Profesionals. 4th edition. Chicago, IL: American Dietetic Association; 2006.

3. The National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Total Water and Macronutrients. The National Academies of Sciences, Engineering, and Medicine website. Published 2005. Accessed March 21, 2018.

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