Overview
This lecture explores the importance of water in the human body, how it is regulated, potential effects of dehydration and over-hydration, and recommendations for daily water intake.
Water in the Human Body
- The human body is 55-60% water on average, with babies at 75% at birth.
- Water composition decreases to 65% by a child’s first birthday.
- Major organs have high water content: brain/heart (75%), lungs (83%), and bones (31%).
Functions of Water
- Water cushions and lubricates joints.
- It regulates body temperature.
- It nourishes the brain and spinal cord.
Water Loss and Replacement
- Adults lose 2-3 liters of water daily through sweat, urine, bowel movements, and breathing.
- Fluid loss must be replenished to maintain a balance and avoid health issues.
Regulation of Hydration
- The hypothalamus senses low water levels and signals release of antidiuretic hormone.
- Antidiuretic hormone helps kidneys reabsorb water, concentrating urine.
- Dehydration can lead to low energy, mood changes, dry skin, low blood pressure, and cognitive impairment.
- Over-hydration (hyponatremia) dilutes sodium, causes cell swelling, and may result in severe health issues.
Recommended Water Intake
- Previous advice said to drink eight glasses daily; now intake depends on weight and environment.
- Recommendations: 2.5-3.7 liters/day for men, 2-2.7 liters/day for women.
- Needs adjust with health, activity, age, and climate.
Sources of Hydration
- Water, coffee, tea, and other beverages contribute to hydration.
- Foods provide about 20% of daily water; fruits/vegetables are over 90% water.
Health Benefits of Hydration
- Proper hydration may lower stroke risk, help diabetes management, and reduce some cancer risks.
- Feeling, thinking, and functioning are improved by adequate hydration.
Key Terms & Definitions
- Antidiuretic hormone — a hormone that signals kidneys to reabsorb water.
- Aquaporins — channels in kidney cells that allow water absorption.
- Dehydration — condition of insufficient water in the body.
- Over-hydration/Hyponatremia — excessive water intake causing dangerously low sodium levels.
Action Items / Next Steps
- Calculate your daily water needs based on weight and activity level.
- Monitor daily hydration, including both liquids and high-water foods.
- Review dietary sources of water and track intake for a week.