Bones continually change throughout your life, with some bone cells dissolving and new bone cells growing back in a process called remodeling. With this lifelong turnover of bone cells, you replace most of your skeleton every 10 years. During childhood and teen years, new bone grows faster than existing bone is absorbed by the body.

After age 30, this process begins to reverse. As a natural part of aging, bone dissolves and is absorbed faster than new bone is made, and bones become thinner. You are more likely to have osteoporosis if you did not reach your ideal bone thickness (bone mineral density) during your childhood and teenage years.

Why is bone loss so common? Think you know what causes osteoporosis? Think again — some of the causes may surprise you

Causes Of Osteoporosis

1. Low Estrogen in Women: What’s the most common cause of osteoporosis? In general, it’s estrogen deficiency in women. Bone loss accelerates after menopause, when older women have a quick drop in estrogen. Over time, the risk of osteoporosis and fracture increases as older women lose more bone than they replace (in women, bone loss increases around menopause, when ovaries decrease production of estrogen, a hormone that protects against bone loss). Besides this, younger women who stop menstruating — such as thin athletes or girls with anorexia — also have compromised bone density. Having both ovaries surgically removed, called a bilateral oophorectomy, it may also cause osteoporosis and low bone density.
2. Low Testosterone in Men: Man needs both testosterone and estrogen for bone health. That’s because men convert testosterone into bone-preserving estrogen. There’s a clear consensus that when you’re evaluating men with osteoporosis, you always evaluate for testosterone deficiency. Several other hormones play a role in regulating your bone density, including parathyroid hormone and growth hormone. They help orchestrate how well your bones use calcium — and when to build up and break down bone. But too much parathyroid hormone, called hyperparathyroidism, causes calcium loss in the urine at the expense of bone. Less calcium means weaker bones. And as you age, your body produces less growth hormone, which you need to build strong bone. Osteoporosis is typically seen in men older than 65, when production of this hormone declines.
3. Lack of Calcium: Without calcium, you can’t rebuild new bone during the lifelong process of bone remodeling. Bones are the reservoir for two minerals — calcium and phosphorus. You need a constant level of calcium in your blood since many of your organs, especially your heart, muscles, and nerves, depend on calcium. When these organs demand calcium, they’ll steal it from the mineral storehouse in your bones. Over time, as you deplete the mineral reservoir in your bones, you end up with thin, brittle bones.
4. Lack of Vitamin D: Too little vitamin D can lead to weak bones and increased bone loss. Active vitamin D, also called calcitriol, is more like a hormone than a vitamin. Among its many benefits, vitamin D helps your body to absorb and use calcium.
5. A Sedentary Lifestyle: Bones weaken if they aren’t worked. For people who are sedentary or have a condition like paralysis or muscular dystrophy, bone loss happens quickly. As a cause of osteoporosis, this one’s in your hands. You can help “remodel” your bones with weight-bearing exercise, where you’re putting gentle stress on bones.
6. Thyroid Conditions: High levels of thyroid hormone have long been linked to an increase in bone loss. That’s always been a concern of most physicians, but if you look at the long-term bone densities of patients who are on high doses of thyroid pills, they’re not dramatically different, and their fracture risk isn’t dramatically different. Still, most doctors would agree that anyone on high doses on thyroid hormone can benefit from getting regular exercise and taking enough calcium and vitamin D. These lifestyle factors are potent ways to manage your overall fracture risk, along with monitoring bone density with testing.
7. Smoking: Smokers suffer from lower bone density and a higher risk of fracture than non-smokers. Studies on smoking and bone health have turned up a host of other dire effects, from direct toxic effects of nicotine on bone cells to blocking the body’s ability to use estrogen, calcium, and vitamin D.
8. Medications: Taking certain medications may lead to bone loss and an increase in bone fractures. Most common are corticosteroids, also known as cortisone, hydrocortisone, glucocortisoids, and prednisone. These drugs are used to treat asthma, rheumatoid arthritis, psoriasis, colitis, and a wide range of other conditions. Antiseizure drugs are linked to bone loss, as well.
9. Medical Conditions: A host of medical conditions can lead to bone loss, from genetic diseases like cystic fibrosis to digestive diseases to the tumors called multiple myeloma, which infiltrate bones with abnormal cells. Abnormal calcium excretion also contributes to bone loss. Some people just don’t trap calcium like they should, and they excrete it through the urine at the expense of the bone.
10. Too Much Alcohol: Alcohol can arrest bone remodeling and increase your calcium loss. Being tipsy increases the risk of falling, and with osteoporosis, that means you’re risking a fracture.