Short of fretting about breaking a leg on the ski slope, you probably don't think much about your bones. "Most women are totally clueless about bone health," says endocrinologist Kendall Moseley, M.D., of the Johns Hopkins Bayview Metabolic Bone Center. Some 94 percent of them don't worry about their skeletons, according to a recent National Osteoporosis Foundation survey, even though one in five women under 30 already has osteopenia, or low bone density, a pit stop on the way to full-blown osteoporosis. Luckily for you, protecting your frame is easy if you know which bad behaviors to avoid.
The Hard Truth
They may feel rock solid, but bones are actually living tissues made up of myriad layers of collagen, proteins, and minerals. All that stuff is so tightly packed that your inner thighbones, for example, can withstand up to 1,200 pounds of pressure without snapping.
(That's why athletes, like pro snowboarder Shaun White, can suffer a brutal crash and still walk away in one piece.)
It's pretty impressive, considering your frame is always in flux: Through something called bone remodeling, bone constantly breaks down and rebuilds itself, giving you a completely new skeleton every 10 years, though you lose more bone than you make after age 30. That's why it's crucial—starting now!—to stock up your reserves by feeding bones their favorite food: calcium. (Compounding the need for a super-solid base: Your levels of estrogen, the other major bone booster, begin to drop after you turn 30, allowing bones to further break down and lose their strength.)
Bone-Weakening Food Fads
Gwyneth Paltrow's uber-strict macrobiotic meal plan became way less enviable when she admitted she'd developed osteopenia in her midthirties.
"Women who stick to severely low-calorie diets often have the bone health of someone twice their age," says Bart Clarke, M.D., an endocrinologist at the Mayo Clinic.
An unbalanced diet can leave you lacking in bone-fortifying vitamins and minerals, and it's not just celeb skeletons at stake. Studies show that more 20-somethings are cutting down on dairy these days, and that 68 percent of women don't get enough calcium from their food. If you're not a fan of milk or cheese, you can up your calcium intake with beans and nuts such as almonds. Protein from plants and lean meats can also help you hang on to bone mass, says Moseley.
OD'ing on Exercise
Sure, there are worse addictions than exercise, but overtraining can be murder on your bones. When a young woman loses too much body fat (indicated by a BMI lower than 18), her ovaries quit producing estrogen, grinding bone renewal to a halt, says endocrinologist Felicia Cosman, M.D., senior clinical director of the National Osteoporosis Foundation.
What's more, studies show that an excess of some workouts are worse for your skeleton than others. Overdoing it in the pool or on the bike or elliptical machine may actually cause you to lose bone density. Scientists think that moderate pounding on your bones—the kind that comes from impact exercises like walking, running, or weight training—is key to triggering your skeleton to lay down more minerals.
Clarke advises doing weight-bearing aerobic exercises (think running stairs, kick-boxing) three days a week and strength training (squats, pushups, triceps dips) for 15 minutes three days a week. With the right routine, some women can increase their bone density by as much as 2 percent a year, even if they're over 30.
Sneaky Calcium Robbers
If your lifestyle stretches you thin (i.e., you have little time to relax, eat a healthy diet, or get ample rest), you should be on high bone alert—even if you pop the recommended 1,000 milligrams of calcium every day. Excessive amounts of caffeine, salt, and alcohol can all interfere with your body's ability to retain the mineral. Too much caffeine, for instance, can cause your body to flush out calcium before it's properly absorbed. Your best bet is to chug no more than two cups of joe a day; better yet, stick to one morning latte (its milk is a mini calcium boost).
Likewise, don't sip more than one or two alcoholic drinks a day, says Moseley, and rein in your daily sodium intake to 2,400 milligrams (or one teaspoon). Certain medications, including some antidepressants and contraceptives, can also deplete your calcium supply, says Cosman. Always make sure to ask your doctor about potential bone side effects before starting new prescription meds.
ARE YOU SHRINKING?
Gravity doesn't just pull at your face and breasts; it also does a number on your bones by flattening the feet and compressing the disks in your spine. The process speeds up as you age: women may shrink by up to a third of an inch every decade after age 40, and by 80, most will have lost 1.3 inches of height. While there's nothing you can do about gravity, you can slow down its effects by being good to your bones right now.