Too much iced tea is linked to kidney stones


As much of the nation gasps through the last steamy hot days of summer, there's mixed scientific reviews for some of the season's pleasures and dangers.

First, let's talk iced tea.

People gulp it down this time of year. But researchers at Loyola University of Chicago point out too much of the brew can boost the odds of kidney stones, a urinary tract disorder that affects about 10 percent of Americans at some point.

Tea, particularly black tea, contains high concentrations of oxalate, one of the chemicals that combine with calcium to form stones that can painfully lodge in the urinary tract.

Dr. John Milner, an assistant professor of urology at Loyola, noted that people are at greater risk for kidney stones if they don't drink enough fluids or become dehydrated from sweating.

But people who drink more iced tea rather than water during the hottest days might be doing themselves more harm than good. Of course, hot tea has the same ingredient, but about 85 percent of the tea consumed in the United States is iced. Milner said people don't have to give up the beverage entirely, just drink it in moderation along with water and maybe some fresh lemonade -- full of citrates that help inhibit kidney stone growth.

Men are about four times more likely than women to develop kidney stones, and the risk rises sharply after age 40. Postmenopausal women with low estrogen levels and women who have had their ovaries removed are also at increased risk.

Well, surely sitting before a cooling fan is a good way to beat the heat, right?

Not always, according to a team of British researchers who reviewed several decades of evidence about fan effectiveness and published their findings recently on the Cochrane Library website.

Fans are generally good when they circulate us air that is at least a few degrees below body temperature and not aimed directly at us, but may actually make us hotter when used at temperatures above 95 degrees Fahrenheit.

While the moving air may make a person feel cooler, in fact the warmth just makes them sweat more and lose fluids and electrolytes at a pace that results in heat exhaustion.

This is a particular concern for the very old and very young, who have more difficulty sweating and regulating their temperature, making them more vulnerable to heat illness, the researchers said.

Still another study published last winter showed that the so-called exercise or couch-potato pill can help mitigate heat stroke. The condition occurs when the body exceeds 104 degrees and can't effectively cool itself due to dehydration or other factors, such as heavy exercise.

Right now, the only emergency treatment for heat stroke is aggressive cooling in an ice bath or with ice packs to bring down body temperature.

Although heat strokes get the most attention when an athlete is struck down, children, the elderly and anyone working outdoors in extreme heat also are at risk.

A recent study in the American Journal of Preventive Medicine noted the number of heat-related injuries treated in emergency departments more than doubled between 1997 and 2006. In that time, an estimated 55,000 people were treated for heat stroke.

The experimental drug AICAR debuted in 2008 with findings that it could build muscle and improve endurance in "couch-potato" mice, those that were completely inactive.

For the heat-stroke experiment, scientists at the University of Rochester and Baylor College of Medicine in Houston gave the drug to mice genetically predisposed to have a heat-stroke type of response when exposed to very high temperatures or when exercising under warm conditions. The mice experience uncontrolled muscle contractions, resulting in the fatal breakdown of muscle tissue that releases toxic levels of potassium into the bloodstream.

But when the mice were given AICAR -- even just 10 minutes before being put under heat stress -- they didn't have the muscle contractions, said Dr. Susan Hamilton, who heads molecular physiology at Baylor and led the study, published in the journal Nature Medicine earlier this year.

Hamilton said the drug or something similar could particularly help individuals who are identified with similar genetic traits that make them more sensitive to extreme heat when they exercise.

Want to leave your comments?

Sign in or Register to comment.