In response to heat waves across the US, NWS Las Vegas, the National Weather Service for southern Nevada, northwestern Arizona and southeastern California, posted an extreme heat warning on X. The warning cautioned residents not to drink caffeine because it speeds up dehydration, which can contribute to heat stroke and exhaustion.
NWS Las Vegas's post quickly made headlines. These headlines said that Americans were being "warned not to drink coffee in three states" because it was "lethal in a matter of minutes." This all seemed extreme to me, so I reached out to three dietitians to find out if we should actually stop drinking coffee in the heat.
"People love to hate on coffee consumption, we're either drinking too much, too little, it's better for you iced versus hot -- it's almost hard to keep up," says Brigitte Zeitlin, registered dietitian and founder of BZ Nutrition.
Does coffee dehydrate your body?
"Caffeine, the main active ingredient in coffee, does have a mild diuretic effect," explains Jessica McAllister, MS, RDN, a registered dietitian based in Honolulu, HI. "However, the common idea that drinking coffee automatically causes significant dehydration, especially in hot weather, is an oversimplification that deserves a closer look."
A diuretic is a substance that increases the production of urine. Though coffee mildly has this effect, McAllister states that for healthy individuals, moderate coffee intake doesn't cause dehydration, but can instead contribute to daily fluid intake.
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Zeitlin adds that what is being talked about in NWS Las Vegas's post is caffeine, which isn't just in coffee. It can also be found in sodas, energy drinks and chocolate. She advises that people keep their caffeine intake to about 300mg daily. This is about 1-2 cups (8-16 ounces of drip coffee) or 1-2 shots of espresso daily. If you stick to this and are otherwise healthy, Zeitlin states that you don't need to be concerned about the outside temperature.
Amelia Ti, a registered dietitian and diabetes educator in New York City, who is also part of CNET's medical review board, adds, "It's not a major concern unless you're already at risk (e.g., high blood pressure or other cardiac issues) or heat-sensitive. The main concern with drinking coffee when it's hot out is that caffeine may mask early signs of dehydration or overheating, especially if you're sweating a lot or not replenishing fluids adequately."
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