Study links hydration to better health: Is water the answer?

From the desk of
Robb Wolf
ScienceStudy links hydration to better health: Is water the answer?

If you want to live a longer and healthier life, you need to drink more water.

That’s how the media is reporting the results of a recent study published in The Lancet, a longstanding peer-reviewed academic journal. The study linked higher blood sodium levels (a proxy for dehydration) to higher risks of chronic disease and death in over 11,000 middle-aged adults. More moderate sodium levels (though not the lowest levels) were linked to lower mortality rates.

Slam dunk, right? Actually, I’d prefer to ask a few questions first. I don’t seek to be a contrarian, but I am keen to examine data from multiple angles before drawing conclusions. For example, are there other factors that may be influencing those correlations? Is serum sodium an accurate marker of hydration? And why isn’t anyone talking about the results of the study’s low-sodium group? Spoiler alert: They didn’t fare well.

While news outlets create splashy headlines to make waves, I’d prefer we calm the waters. It may not attract a lot of surfers, but it does allow us to see much deeper into the ocean of data. Let’s start by examining the paper itself – then we’ll dive into the questions I laid out above.

Overview of the Lancet Study

In this observational study published in January 2023, scientists from the National Institutes of Health (NIH) analyzed health data on 11,255 middle-aged adults between ages 45 and 66. Specifically, they sampled serum sodium levels 5 times over a subsequent 25 years, and compared those levels with markers of aging, chronic disease risk, and death. They excluded, as best they could, adults with conditions or medications that could affect serum sodium levels.

Below are the highlights of what they found. Note that normal serum sodium is in the range of 135–146 mmol/L.

  • People with optimal serum sodium (137–142 mmol/L) functioned like a control group, to be compared against those with high-normal and low-normal serum sodium.
  • People with low-normal serum sodium (135–136.5 mmol/L) had a 71% increased risk of all-cause mortality compared to people with mid-normal serum sodium.
  • People with high-normal serum sodium (144.5–146 mmol/L) had a 21% increased risk of premature death compared to people with mid-normal serum sodium.
  • Above 142 mmol/L, people were more likely to suffer heart failure, atrial fibrillation, stroke, dementia, chronic lung disease, diabetes, and other chronic conditions. They also scored worse on biological age (BA). BA is not one’s true (chronological) age, but rather it’s a figure calculated based on biomarkers of overall wellness, such as blood pressure, cholesterol, blood glucose, and more.

Let’s review how this data is being presented to the public now.

What’s Being Reported About Hydration and Health

The media has interpreted this study as evidence that we need to drink more water. Check out these two headlines, for example:

  • Drink up: Large study finds that not consuming enough water increases risk of death by 20%NY Post
  • Staying hydrated is linked to a longer, healthier life, new study suggestsCBS News

Even when reporting nuanced science, news outlets focus on one potential conclusion to get your attention. Insufficient hydration means you die young? Print that baby out!

These titles don’t surprise me. What does, however, is that nobody is reporting the statistics associated with the lowest sodium group. Here comes the fun part: thinking for ourselves!

Questions About These Conclusions

The conversation surrounding this study needs more nuance. Here are some questions to help.

Is serum sodium an accurate marker of hydration status?

In mice, significant water restriction increases serum sodium levels and shortens lifespans. This makes sense. Water is an important component of blood, so significantly decreasing water intake would reduce one’s blood volume and increase the concentration of sodium in that volume. Limit water intake for a long time, and chronic dehydration produces many negative health consequences.

However, elevated sodium isn’t a perfect proxy for fluid needs. Sodium status is also influenced by factors such as medications, insulin function, sweat loss, sodium consumption, and many other health conditions. While the researchers attempted to control for these factors, it’s far too complex to accomplish.

Could the study population really be dehydrated for decades?

The population studied were pretty healthy, and dehydration is rare in healthy adults. Why? Most people have adequate fluid access, a functioning thirst mechanism, and plenty of societal reminders to hydrate—like those catchy headlines, for instance!

Dr. Rick Lange of Texas Tech summed it up well: “It’s hard to believe that people are really under-hydrated for a period of 25 years.” Again, perhaps something else is influencing their sodium status.

What else might explain the correlations?

It’s crucial to ask this question of any observational study. Just because two variables trend together doesn’t mean one causes the other.

Consider the relationship between height and reading ability: as height increases, reading ability increases. Does this mean that shorter adults can’t read Tolstoy? Nope! It just means that babies and toddlers—the shortest folks around—skew the data.

What hidden variables might be confounding the Lancet data? Are people with higher sodium levels more likely to eat ultra-processed diets? They could be, as processed foods tend to be saltier than whole foods. Then salt takes the blame for bad health outcomes, even though overeating and nutrient deficiencies are the real culprits.

That’s just one possible confounder. Remember, a long list of factors affects sodium status. The authors adjusted for a few, but it’s simply impossible to account for all of them.

Why isn’t anyone talking about the low-sodium cohort?

Compared to the control group (moderate serum sodium), the highest sodium group had a 21% increased risk of premature death. That’s the figure plastered all over the internet. But looking at the data, you could also write a headline like:

Drinking too much water increases risk of death by 71%, study finds.

That’s right. The lowest serum sodium group had a 71% higher risk of all-cause mortality than the control group. What reliably lowers sodium levels? Drinking too much water.

Again, the risk of death was MUCH higher in the low-sodium group than in the high-sodium group. It’s the bigger story, so why didn’t anyone print it? I’ll leave that for you to ponder.

Finding Your Hydration Sweet Spot

Drinking more water regardless of your age, diet, and activity level is NOT a reliable way to enhance health and longevity. It might prevent dehydration, but it raises the risk of overhydration. That’s a bad trade. Instead, find your hydration “sweet spot.”

To do so, rely on an ancient, effective, internally regulated mechanism: thirst. If you’re thirsty, drink something. If you aren’t, your body probably won’t benefit from more water. I’ll caveat that as we lean into our wiser years, our thirst mechanisms may become less reliable. So drinking on a set schedule may be helpful for seniors, but it shouldn’t be a standard protocol for everybody.

Adding salt to your water can also help to ensure you don’t deplete sodium levels while hydrating. Contrary to popular belief, sodium is an important component of healthy hydration.

It’s simple to maintain your hydration sweet spot. Just sip electrolyte water to thirst. It may make for a lousy headline, but it’s a fantastic way to care for your health.

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