Remembering to drink enough water is easy during the summer, when higher temperatures and outdoor activities drive the point home. But staying adequately hydrated is just as important during the winter.

Environmental humidity plays a role, said Stavros Kavouras, who directs the Hydration Science Lab at Arizona State University in Phoenix. Central heating causes drier interior environments during the winter, which can lead to increased water loss simply from breathing.

That's not the only challenge. In cold environments, the kidneys actually excrete more urine, said Joseph C. Watso, a postdoctoral research fellow at the Institute for Exercise and Environmental Medicine in Dallas.

"It's a small change that could potentially make a difference," he said. "If you're not sweating, you might forget to drink adequate water."

Dehydration sets in when the body loses more water than it takes in.

Even minor dehydration – the level at which people begin feel thirsty – is linked to difficulty concentrating, poor memory and bad moods. And studies have shown people who chronically consume a low amount of water seem to be at higher risk of developing chronic kidney disease, kidney stones and urinary tract infections. "High urine flow seems to be protective," Kavouras said.

Kavouras and his colleagues found mild dehydration impaired the function of cells that line blood vessels almost as much as smoking a cigarette. Dehydration also has been linked with inflammation, artery stiffness, blood pressure regulation and other factors that can raise the risk of heart disease and stroke.

Research also has linked poor hydration to diabetes. "Diabetes is a lifestyle disease that's associated with what we eat, what we drink and how physically active we are," Kavouras said. "Hydration seems to be part of this recipe."

Exactly how much water people need can vary.

"Our water needs change from day to day based on factors such as environmental temperature and activity level," Kavouras said. "If you are an Ironman athlete who trains four hours per day, your water needs are higher than somebody who is sedentary."

In general, the federal Institute of Medicine suggests women take in 2.7 liters and men 3.7 liters of water per day. That might sound like a lot, but because food contributes about 20% of the daily water total, women should drink 8, 8-ounce glasses and men 12, 8-ounce glasses.

"It's underappreciated that many fruits and vegetables are 90 to 95% water," Watso said. "Eating more fruits and vegetables can certainly help you stay hydrated." Soup, an old winter standby, also counts. "Just be sure to avoid soups with very high amounts of sodium."

Watso recommends people keep a refillable water bottle with them and sip on it all day. "Your body can only process water at a certain rate, and if you drink too much too (quickly), the excess will be excreted," he said.

Experts say fluid from tea and coffee – even that eggnog latte – counts toward hydration. Even soda and juices technically contribute to one's daily fluid intake, although experts do not recommend them because of their high sugar content. Alcohol, however, doesn't make the cut.

Kavouras advised people to pay attention to how often they use the bathroom. Adults should urinate six or seven times per day. Dark yellow or orangish urine is a sign to drink up.

"Drinking water throughout the day is one of the most effective things you can do to improve health and well-being."

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