Chapter 52
How Much Water Should You Drink, Then?
If you look at blood samples taken at different times, you find that between 20 and 30 percent of older adults are chronically dehydrated. They have an increased risk of heart attack, pneumonia, and blood clots, which doubles their likelihood of being disabled two years later. How do you know if you’re dehydrated? Young people can check the color of their urine. The gold standard for hydration—or, more accurately, the pale-gold standard—is straw yellow, meaning a light yellow. A darker yellow, amber, or brownish tint indicates dehydration in athletes, pregnant women, and breastfeeding mothers, as well as in the broader population; in older adults, however, that doesn’t seem to work. Of 67 different parameters—including urine color and volume, a dry mouth, or feeling thirsty—not a single one proved consistently useful for determining hydration status in those over 65. Only the fact that the older men and women were tired and drank too little between meals could predict impending dehydration.
Based on the current state of knowledge, experts at the World Health Organization (WHO) and the U. S. Institute of Medicine recommend between eight and eleven cups of water a day for women and ten to fifteen for men. This includes water from all sources, not just beverages. We get about four cups of water daily from food and from our body’s own production (for example, through fat burning), so the guidelines can be roughly reformulated into the daily recommendation, with moderate physical activity and a moderate ambient temperature, to drink four to seven cups of water a day as a woman and six to eleven cups as a man. Older people’s kidney function, however, is usually limited to about three to five cups per hour, so under normal circumstances you shouldn’t exceed that limit. More than the recommended amount of fluid can dangerously dilute the electrolytes in the brain.
Which water?
Many people don’t trust the quality of tap water, but bottled water may not be any cleaner than water straight from the faucet. But what does that say? Drinking-water quality is more than preventing waterborne diseases. In fact, our fight against microbial contamination has brought about a new drinking-water contamination—in the form of disinfectant by-products caused by chlorination. In my video see.nf/water, I weigh the possible bladder-cancer risks and assess the effectiveness of two refrigerator filter systems (Whirlpool and GE) and three pitcher filter systems (Brita, PUR, and ZeroWater) for water purification.
Beverages—a ranking from best to worst
What are the best beverages besides water? The chart below comes from the comprehensive study of hundreds of pooled meta-analyses and systematic reviews and shows protective, neutral, or harmful associations with diet-related chronic diseases.
As expected, sweetened beverages such as carbonated soft drinks were rated as the most harmful, but 14 percent of studies found protective effects for soft drinks. How is that possible? In most cases, these were references to cross-sectional studies—for example, one found that eighth-grade girls who drank more soft drinks were slimmer than girls who drank less. That was only a snapshot, though. Which do you think is more likely? Did the heavier girls weigh more because they drank less soda, or did they drink fewer sugary drinks because they were heavier? Avoiding such beverages is more likely a consequence of obesity than a cause, yet they were classified as protective because a greater amount of that beverage was associated with a lower prevalence of a disease.
Flaws in study design may also be the reason for the findings about wine. The review of reviews was published in 2014, before the revolutionary realization that supposedly healthy “moderate” alcohol consumption was nothing more than an illusion. (More on addressing the systematic error of misclassifying former drinkers as lifelong abstainers elsewhere.) Sometimes, however, there are truly unexplained connections. For example, one of the soft-drink studies found that higher consumption was associated with a lower risk of certain types of esophageal cancer. Let me guess. Did Coca-Cola fund that study? Yes, Coca-Cola funded it. Do comparable conflicts of interest explain the “protective” effect of milk in some studies? Were those funded by the National Dairy Council? In fact, there were even more conflicts of interest in the milk studies than in the soda studies. Studies funded exclusively by industry are four to eight times more likely to produce results that favor the financial interests of their sponsors.
But even if you subtract the bias from financial interests, there could be legitimate reasons to associate protective effects with consumption of cow’s milk. After all, people who drink milk reach for soda less often, which is even more harmful, so milk drinkers may achieve better outcomes. But perhaps there is more behind it than just relative advantages. Not even something with as nasty a reputation as tobacco is entirely bad. More than 40 studies consistently showed protection against Parkinson’s disease, thanks to nicotine’s effects on the brain. Even secondhand smoke can protect. Of course, you still want to avoid it. Tobacco may lower Parkinson’s risk, but if you smoke, you increase your own risk of a stroke, an even more life-threatening brain injury—not to mention lung cancer and heart disease, which have cost millions of Americans their lives since the publication of the first report by the U.S. Surgeon General against smoking.
Fortunately, we can eat nicotine-containing vegetables and get closer to the benefit without exposing ourselves to the risks (see.nf/nightshades), and the same concept could apply to dairy products. Milk consumption is associated with an increased risk of prostate cancer, leading to recommendations for men to cut back or minimize it, but dairy products are also associated with a lower risk of colon cancer. It appears that this protective effect is due to calcium. Fortunately, we can leave out the harm and keep the benefit by eating plants high in calcium such as leafy greens and beans.
I have already covered dairy products in more detail and also explained the positive effects of coffee consumption. The overview there shows, however, that each cup of coffee could be a missed opportunity to drink something even healthier, such as a cup of tea.
The healthiest milk
These days there’s a new landscape in dairy products, because now milk is made from everything from almonds to oats, and the selection is so enormous that large dairy operations are threatened with bankruptcy. The healthiest of all options is probably soy milk. Check out my video see.nf/milks as well. None of the plant-based milks contains lactose—a benefit worth emphasizing.
Most adult humans are lactose intolerant, meaning they can’t properly digest milk. Over the course of childhood, our body makes less of the enzyme that, in most of us, breaks down the milk sugar lactose, which makes sense, since milk is for babies. Why would we still need to be able to digest milk after weaning? That’s likely why most people around the world suffer from symptoms such as bloating, abdominal pain, intestinal gas, and watery stools, or even nausea and vomiting.
It’s estimated that a two-thirds majority of people worldwide have difficulty absorbing lactose. In the United States it’s more like one in three, but 95 percent of Asians, 60 to 80 percent of African Americans and Ashkenazi Jews, 80 to 100 percent of Native Americans, and 50 to 80 percent of Hispanic Americans have trouble digesting milk. People of Northern European ancestry are most likely to manage it throughout adulthood. So when you say everyone should drink milk, it sounds like racial discrimination in U.S. nutrition policy. Spoiler alert: Not everyone in America is from Northern Europe.