Bone is living tissue; every day your body breaks down old bone and new bone grows in its place. Until your 20s, you actually make more bone than you lose, but in early adulthood, the building process comes to a halt, and you start losing bone faster than you replace it. That’s why it’s essential to build strong bones when you’re young. Strong bones aren’t as vulnerable to a bone-destroying disease called osteoporosis. Osteoporosis means “porous bone,” and it means that bone has become less dense and weaker.

The problem is that you can’t feel your bones getting weaker, so you may not even know your bones are at risk until you break one. Just a generation ago, physicians thought that developing weak bones was just part of the aging process. But now we know there is plenty we can do, at every age, to develop healthy bones and keep them that way.

Exercise is essential for building — and maintaining — strong bones. Experts have known that resistance training and weight-bearing exercise will fortify your frame, but some new research suggests that the higher the impact, the better. One study, done at the University of Missouri in Columbia, Mo., found that running boosts bone mineral density more than resistance training.

Although running might be the “best” way to build bone, it’s not the only way. Your bones will also benefit from walking, hiking, dancing, doing “step”-type aerobics, jumping rope, and playing basketball or tennis. Any type of weight-bearing exercise, i.e., activities that force you to work against gravity, will help. The impact of activities such as these tells your bones to produce cells called osteoblasts, which strengthen your skeleton. If you prefer to ride a bike or swim, its extra important that you incorporate resistance training into your routine; try lifting weights, which also sends the cell-building message to your bones.

The National Osteoporosis Foundation recommends 30 minutes of weight-bearing exercise on most days of the week, but you don’t have to do it all at once. You might walk for 10 minutes during your lunch break, do another 10 later in the afternoon, and then do 10 more after dinner. The foundation also recommends a strength-training regimen that works all the major muscle groups. Aim to complete one or two sets of 8–10 repetitions of exercises such as bench press, biceps curls, modified pushups, squats, lunges, etc.

Osteoporosis is a problem that is most often linked to older women, but they’re not the only ones who are at risk. Some two million American men have the disease, and another 12 million are at risk. Osteoporosis in men is underdiagnosed and underreported. The disease isn’t as widely studied in men, either. Men who smoke, don’t exercise, don’t take adequate calcium, and have a family history of the disease are at particular risk for developing the disease.

Experts know much more about osteoporosis in women, and the American College of Obstetricians and Gynecologists offers guidelines about testing for the disease: Postmenopausal women who are 65 years old should have the screening test known as the dual-energy X-ray absorptiometry (DEXA). Bone mineral density testing may be recommended for women who are postmenopausal and younger than 65 if they have at least one risk factor for the disease. Risk factors include family history, previous fracture, menopause before age 45, poor nutrition, cigarette smoking, low weight and body mass index, and estrogen deficiency. According to the National Osteoporosis Foundation, only 15 percent of women 45 or older believed they were at risk for osteoporosis, yet many of them had two or more risk factors for the disease.