High-impact exercise is one way to maintain bone density, but it may not sustain the calcium levels you need for the long term. In a 1995 study of college basketball players at the University of Memphis, researcher Robert Klesges's bone-density scans revealed significant mineral loss in the athletes during their four-month season. To find out why, his scientists literally wrung out the jerseys after a practice. "Our analysis showed huge expenditures of sodium," says Klesges, "which we expected, and surprising amounts of calcium, which we didn't."

The next season, to counteract the mineral flush, Klesges advised the players to supplement their diets with up to 2,000 milligrams of calcium per day, administered by stirring inexpensive calcium lactate into an energy drink. That season, "bone loss was virtually eliminated," he says. For five years, the team continued to add calcium to their drinks, with the same results.

His findings, published in The Journal of the American Medical Association in 1996, exposed a common shortfall in the American diet: too little calcium. "Most people don't even come close to the recommended daily allowance of 1,200 milligrams," says Klesges, "but that amount is still not enough for an athlete exercising over an hour each day." Nearly ten years later, most sports drinks still don't contain enough calcium for Klesges. "Without a demand for it, manufacturers simply aren't going to add the mineral's cost to their products," he says.

So how much calcium should you be getting? For most, anything over 2,000 milligrams is overkill; 1,200 a day is plenty for a recreational athlete, says Klesges, and you can meet your needs through milk, dairy products, calcium-fortified orange juice, and tofu. Each serving contains about 200 to 300 milligrams of calcium. Going on a long workout? Nab an additional 200 milligrams of the stuff for every hour beyond the first.

Bill Holland follows this advice religiously. He still rides as much as ever, but now he also rotates in thrice-weekly four-mile runs, plus three trips to the weight room each week, and he takes 1,200 milligrams of calcium a day. Since his first bone scan, in 2001, he's reversed his bone loss and seen 1 to 2 percent increases in density each year.

"Someday," says Holland, "I might have average-strength bones again."