When the Body Forgets to Ask for Water

The fading thirst reflex after 60 isn’t just an inconvenience—it may be one of the most overlooked causes of heart and brain stress.

This past weekend, Louise and I took our weekly 2-mile hike through Portland’s Forest Park, climbing the equivalent of 30-40 stories up trails that follow the urban hills of the Tualatin Mountain range. My heartbeat, which usually only gets into the low 130s on such a hike, was spiking 145 on my Apple watch.

That was when I realized the only liquid I’d drank since before going to bed was a half a cup of coffee. I pulled out a bottle of water and downed about 8 ounces of it; within 10 minutes my heartbeat rate was down to the 120s. (My resting rate is 57.)

Apropos of this, I’ve noticed something over the past few years that both surprised and concerned me: I rarely feel thirsty anymore.

When I was younger, thirst was like an internal alarm clock: loud, immediate, and impossible to ignore. Now it’s mostly silent. My body still gives me signals, of course. My urine will turn dark, my mouth will go dry, or I’ll feel a faint lightness in my head if I stand up too quickly. But the actual sensation of thirst—the prompt that once made me go to the sink and get a glass of water—has nearly disappeared.

It turns out this isn’t just a personal quirk. Once we pass around 60 (I’m 74), the systems in the brain and body that govern thirst lose their previous sensitivity. The hypothalamic osmoreceptors that once reacted quickly to rising sodium levels or falling fluid volume just don’t sound the alarm the way they used to.

At the same time, aging muscles shrink and total body water declines, so we have a smaller margin for error. The kidneys lose some efficiency in concentrating urine, which means we lose more water than we think. Add in common medications in older adults—like diuretics or antihypertensives—and it’s easy to see how dehydration can become a chronic, low-level condition without a senior citizen ever feeling like anything is wrong.

Studies back this up. Surveys suggest that somewhere between a quarter and nearly half of older adults are underhydrated on any given day. UCLA Health has noted that up to 40 percent of adults over 65 experience chronic dehydration. Researchers writing in journals like Nutrients and The American Journal of Epidemiology have described how age-related changes in fluid balance, thirst perception, and kidney function combine to create what they call “low-intake dehydration.”

It’s not the dramatic, hospital-level kind kind of dehydration caused by vomiting or fever. It’s the slow, quiet kind that builds over days or weeks when you simply don’t drink enough because your body doesn’t ask you to.

And here’s where it becomes more than an inconvenience. There’s growing evidence that chronic dehydration in older adults may increase the risk of heart attack and stroke.

The connection isn’t speculative. When you don’t take in enough water, your plasma volume drops. Blood becomes thicker and flows more slowly. That increased viscosity raises the likelihood of clot formation, especially in blood vessels already stiffened by age or plaque.

Researchers who followed older adults in the Adventist Health Study found that those who drank five or more glasses of water a day had a significantly lower risk of fatal coronary heart disease than those who drank two or fewer, even after accounting for lifestyle factors. Other studies have pointed to how rising blood sodium concentration and reduced plasma volume can trigger vascular inflammation, increase endothelial stress, and strain the heart.

Even modest dehydration can provoke the body to constrict blood vessels and raise heart rate to maintain pressure. In someone with aging arteries or mild diastolic dysfunction, that extra strain adds up.

A NIH-supported analysis has suggested that staying well hydrated may reduce the long-term risk of heart failure. There’s also research connecting dehydration and short-term stroke risk in people with atrial fibrillation.

When blood thickens, clots can form more easily and travel to the brain. A recent paper in Progress in Cardiovascular Diseases outlined how both physiological aging and cardiovascular medications make older adults uniquely vulnerable to this cycle. The authors weren’t fearmongering; they were sounding an alarm modern medicine has largely overlooked.

To be clear, no one is claiming dehydration alone causes strokes or heart attacks. Much of the evidence is observational, and many of the mechanisms are inferred from lab and animal studies. But the convergence of data, biologic plausibility, and lived experience points in the same direction: once you’re north of 60, letting yourself slip into even mild dehydration is a cardiovascular stressor. But you might never feel thirsty while it’s happening.

That puts the burden back on awareness and habit, which is trickier than it sounds. I’ve had to train myself not to wait for thirst as the signal to drink water. Instead, I pay attention to things I used to ignore: the color of my urine, whether my mouth feels slightly tacky, whether my energy dips for no obvious reason.

Some days I do well. Other days I look at a glass sitting next to me in the late afternoon and realize I never touched it. I’ve started keeping water or green drinks at arm’s reach, drinking a glass in the morning before coffee, and sipping throughout the day whether I feel like it or not. I also remind myself that fluids don’t just come from water; herbal teas, broth, juicy fruits, and soups all help. The goal isn’t to drown myself; it’s to stay ahead of the deficit my body no longer warns me about.

The research suggests that roughly 1.7 liters a day is a reasonable floor for most older adults, adjusting for heat, activity, and health conditions. But the exact number matters less than the consistency. I’ve also found that pairing water with routines—like writing, reading, doing my radio show, or meals—keeps it effortless.

None of this is glamorous, but neither is a stroke. Every cell and capillary depends on hydration to do its job. When we’re young, the scaffolding of youth masks a lot of neglect. Past 60, the bills start to come due.

There’s a cultural habit of treating hydration as a lifestyle tip rather than a medical issue. But for older adults, it may be one of the simplest and most powerful cardiovascular interventions we’ve overlooked. The blood gets thicker, the vessels get stiffer, the kidneys get slower, and the brain gets quieter about thirst. That’s a setup that deserves attention.

I’m not interested in alarmism; I’m interested in staying alive, aware, and functional for as many years as I’m given. Water is cheaper than heart surgery and quieter than an ambulance.

So I no longer wait to feel thirsty. That signal retired before I did. I watch my body’s other indicators, I err on the side of drinking before I need it, and I treat hydration not as an afterthought but as part of aging consciously.

If you’re over 60 and you’ve noticed the same thing—that you almost never feel thirsty anymore—you’re not imagining it. The system has changed. Fortunately, we can change with it.