Influence of age on thirst and fluid intake

Q: Is it true that thirst disappears after 60 years?

Krishna: This is what research (1,2) says:

The sensation of thirst decreases, not fully disappears,  with age, as does the amount of water in our bodies, which makes seniors more at risk for dehydration.

You most likely know a feeling of thirst – or even of being parched, when you are young.  But as you age, that sense of thirst diminishes. So even when your body needs to be replenished with water, you might not realize it.

Because of that, many older adults don’t drink enough liquids. “By the time they are thirsty, that’s already an indication of early dehydration". 

Seniors are also at greater risk for dehydration because of how body composition changes with age. Older adults have less water in their bodies to start with than younger adults or children.

Many of the earliest signs, like dry mouth, fatigue, dizziness and muscle cramps, are nonspecific and could be easily attributed to other medical conditions, medications or natural effects of aging. Persistent dehydration that causes difficulty walking, confusion, rapid heart rate or other more severe symptoms can land seniors in the hospital.

Kidney problems cause dehydration. As bodies age, the kidneys can stop processing fluids efficiently, which can lead to more trips to the bathroom and fluid loss. Medications can be another cause of dehydration. Many seniors take regular medication for medical conditions and can be unaware of dehydration as a side effect. 

Independently living older adults (over the age of 65 yr) consume adequate volumes of fluids on a daily basis. However, when challenged by fluid deprivation, a hyperosmotic stimulus, or exercise in a warm environment [all of which combine hypovolemia (  a state of low extracellular fluid volume, generally secondary to combined sodium and water loss. All living organisms must maintain an adequate fluid balance to preserve homeostasis. Water constitutes the most abundant fluid in the body, at around 50% to 60% of the body weight) and hyperosmolality( a condition in which the blood has a high concentration of salt {sodium}, glucose, and other substances], older adults exhibit decreased thirst sensation and reduced fluid intake. Full fluid restoration eventually occurs, but full restoration of fluid balance is slowed.

The aging process alters important physiological control systems associated with thirst and satiety. Recent evidence suggests that older men and women (i) have a higher baseline osmolality (the concentration of all the particles dissolved in body fluid) and thus a higher osmotic operating point for thirst sensation (with little or no change in sensitivity), and (ii) exhibit diminished thirst and satiety in response to the unloading (hypovolemia) and loading (hypervolemia-  a condition where your body has too much fluid. Another name for hypervolemia is “fluid overload” or “volume overload.” Your body is made up of 50% to 60% fluid, which includes water, blood and lymphatic fluid) of baroreceptors. A diminished sensation of thirst in the elderly relative to young adults is generally absent when a volume stimulus is absent, despite higher baseline plasma osmolalities.

Compared with the elderly, there are scant data associated with homeostatic control of thirst in children. Nonhomeostatic control of thirst and drinking behaviour may likewise be different for children (as it is for the elderly), as compared with young adults; however, little empirical data exist on this topic. Children rarely exhibit voluntary dehydration for activities lasting 45 min or less; however, drink flavouring and sodium chloride are important promoters of drinking in active children.

Even if you don't  feel thirsty, you can have these other dehydration symptoms

Signs of dehydration aren’t always obvious and can range from mild to severe. Symptoms can include the following: Headache, Nausea, Dizziness, Confusion or disorientation, Dry mouth, Fainting, Loose skin or skin that doesn’t return to normal after pinching, Urinating less than usual, Constipation, Muscle cramping, Fast heart rate, Drop in blood pressure. 

Hot weather season is not the only time when dehydration is a risk. Many seniors are at risk for dehydration throughout the year. Even in winter, it’s important to drink a healthy amount of water throughout the day. Everyone does need to drink an appropriate amount of water for their body weight and level of activity, dehydration or no dehydration. 

Footnotes:

1. https://journals.lww.com/acsm-msse/Fulltext/2001/09000/Influence_of...

2. https://pubmed.ncbi.nlm.nih.gov/11528342/

Other related Qs and answers:

Q: My hands and legs swell in the heat. Why is this?

Krishna: Heat edema. This effect is more common in females. I too face this problem during summer, especially when I exercise, walk or work hard my palms and feet swell and I have this painful sensation.  

 Heat causes the blood vessels to expand (dilate), so body fluid moves into the hands or legs by gravity. The balance of salt in the body is also a risk factor for heat edema. If salt loss is less than normal, the increased salt level draws fluid into the hands and legs.

It’s common to experience edema more severely on hot days. “As the temperature starts to rise, the heat may cause the lower leg vessels to dilate,” or open wider. “That can cause fluids to leak out and get trapped underneath the skin.” With more fluid comes more swelling.

Another explanation for summertime swelling stems from the body’s interest in regulating your core temperature to prevent organ damage. As your heart pushes warm blood away from your intestines and kidneys, it can pool in the legs and arms.

If you suddenly come out of an AC room or car into a very hot  outside atmosphere, you won't even be able to walk with your legs swelling all of a sudden. This is mainly  because of venous insufficiency (or bad vein valves), but there can be other underlying health conditions and reasons too. So if it is severe consult a qualified medical doctor.

One sign that your edema might be dangerous: You can see the memory of your fingerprint after you press into the skin. This is called pitting edema. If a person notices they can press a finger into their leg and it leaves a deep dimple, they should seek medical attention.

Ordinary heat edema can be reduced by following these things like I do ....

Raise you hands above your heart level for sometime, this swelling disappears. Or put them in mild cold water or water that is not hot for about 10-15 minutes. This reduces the swelling for me.  

Other things you can  follow if it is more complicated: Once you’ve ruled out serious problems, you might want to start reducing the swelling. Here are a few things you should try.

• Wear compression socks. This is a common way to treat edema. Compression socks can be purchased online or at a medical supply store. “Wear them like a normal pair of socks during the day. You do not need to sleep in them.” This can make a big impact on swelling. Similarly, you can also look into compression boots, which are inflatable leg sleeves you can wear at home.
• Elevate your legs. Use gravity to help blood flow back toward your core. You do this by elevating your swollen legs. When sitting down, it may benefit you to prop your legs up on a recliner or on 2 to 3 pillows to get your feet above your heart level.
• Give your feet a break. If you work standing up, the occasional break could help blood circulate away from your legs. It would be beneficial to sit for 10 minutes a few times a day during work. This is most effective if you’re also wearing compression socks and drinking plenty of water.
• Cut the salty foods. Diet also plays an important role in keeping edema at bay. “Foods high in salt and sodium may be part of the problem. Among the big offenders are  potato chips, noodles with “flavour packaging,” soy sauce, teriyaki sauce, flavoured jerky, and pickles.
• Drink plenty of water. Being dehydrated can actually lead to more swelling.  You should drink  lots of water on hot days. Your urine should run clear, with no odour. (As it turns out, the color of your urine says a lot about your health.)

Q: Why do we get heat cramps?

Krishna: Heat cramps are painful muscle spasms caused by dehydration and electrolyte loss. They can be brought about by strenuous activity, hot weather, and other causes.

Heat cramps are very painful muscle spasms that occur due to dehydration and loss of nutrients from excessive sweating. They are associated with heavy perspiration. Heat cramps are most common in the abdomen, back, arms, or legs.