Carlos Solis
Dehydration means the body loses more fluid than it takes in. It can happen after diarrhea, heavy sweating, drinking alcohol, fever, or prolonged sun exposure.
Drinking water is the simplest fix. Adults should drink about six to eight cups, about 1.5 liters per day. But studies show the average adult drinks less than half that, which raises the risk of several health problems.
Key symptoms to watch for
Thirst
Thirst is the clearest signal of dehydration. Losing about 2% of body weight as fluid through sweat, urine, bowel movements, or even breathing triggers the brain’s thirst response. You feel it more in hot months because your body produces more sweat.
Beyond plain water, experts recommend electrolyte-rich drinks to help restore kidney function and replace minerals lost in sweat.
More stress and a worse mood
Dehydration affects the mind as well as the body. A study in the Journal of Applied Psychology published last year found that people who drank the recommended 1.5 liters per day had lower cortisol—the stress hormone—than those who did not. Earlier work linked lower water intake to increased tension, while drinking more fluids had the opposite effect.
Dark urine
Urine color is an easy way to check hydration: pale yellow or nearly clear usually means you are well hydrated, while a darker yellow or brown can signal you need to drink more. When you’re dehydrated, urine becomes more concentrated because there is less water to dilute the natural pigment urobilin. Urine can also develop a stronger ammonia-like smell.
That said, dark or strongly smelling urine does not always mean dehydration: medications, diet, infections, or other medical conditions can also change urine color and odor. If these changes do not go away after you drink more, see a doctor.
Trouble concentrating and making decisions
The body is about 60% water and the brain up to 75% fluid, so even mild dehydration hits cognitive function quickly. Even a small amount of fluid loss reduces memory, attention, and coordination. That can show up as trouble concentrating, remembering things, or making safe decisions—for example when crossing a street. People sometimes call these effects “brain fog.”
Headache
The common advice to “drink water for a headache” has merit. The body loses about 2.5 liters of fluid a day on average, and shortages can trigger intense headaches. Experts think that reduced fluid volume in the brain increases pressure on pain receptors and nerves, and drinking water helps relieve that pressure. Most dehydration-related headaches ease within an hour or two after rehydration.
Weakness and fatigue
Dehydration can be one cause of fatigue. When the body loses fluid, the heart has to work harder to maintain blood pressure and oxygen delivery. That extra strain leads to sluggishness, general weakness, and low energy. Professor Lobo adds that older adults feel these effects more strongly. Studies show older patients hospitalized with dehydration stay in the hospital longer and have a 6% higher mortality rate.
Dizziness and fainting
If you lose about 4% of your body weight as fluid, you risk overheating and a drop in blood pressure. That can cause dizziness and, in some cases, fainting. Dehydration is one trigger of fainting, which happens to roughly two out of five adults at some point in life.
Muscle cramps
About a third of people over 60 experience leg cramps. Dehydration is one possible cause. Low fluid levels can go along with drops in salt concentrations, which may trigger cramps. Sodium—the electrolyte that combines with chloride to make table salt—is lost during dehydration, and sodium deficiency is linked to cramps.
How much to drink—and when it can be harmful
Doctors recommend adults drink between 1.5 and 2 liters of water a day, or enough to keep urine a pale yellow. But drinking too much also carries risks. Rapidly drinking large amounts of water can disrupt electrolyte balance, especially sodium, and cause hyponatremia.
Hyponatremia happens when water moves into cells, causing them to swell. That can be dangerous and lead to headache, confusion, nausea, vomiting, and in severe cases seizures or loss of consciousness. The highest risk falls on people who gulp large volumes of water in a short time.
Keeping a safe fluid balance is easier than it sounds: drink regularly throughout the day, watch urine color, and account for higher needs during heat, exercise, or illness. If you have doubts about symptoms or they do not go away after you drink more, consult a doctor.
Based on reporting from Daily Mail
