jenny cares 

Osteoporosis 'snuck up' on me, and at the time I didn't consider myself 'older'.
The list below is interesting, though I've left a lot out that I consider oversimplified. Also, the article neglects to mention that at least one drug given to treat osteoporosis has caused serious problems e.g. multiple teeth abscesses, broken jaws.
.

Adapted from 10 Warning Signs Your Bones Are Thinning | Care2 Healthy & Green Living 
.
HERE ARE THE TOP 10 WARNING SIGNS OF THINNING BONES:
.
1. FRACTURED BONES, BONE DENSITY
i.e. you’ve had more than one fracture...or you’ve had a fracture that seemed unusually severe for the circumstances.
Kim found out she had osteopenia, or mild osteoporosis, when she fractured her ankle simply by stepping the wrong way off a curb. Your bones need to be strong enough to sustain some impact, and if they aren’t, you’ll want to know more about what’s behind that.
Get a bone density test, also called a DXA scan or densitometry, which is a specialized type of X-ray that measures the amount of calcium and other key bone-hardening minerals within each bone segment. 
.
2. THIN, SMALL-FRAMED, GENETICS, EXERCISE 
People with small, delicate frames are likely to develop osteoporosis at a younger age. This doesn’t mean that heavy or big-boned people don’t get osteoporosis; just that people who are thin or small-boned don’t have as far to go before they’re at risk for fracture. 
20-25 years old: we reach peak bone mass and stop building bone;
30-40 years old: we start losing bone.
The rate of bone loss depends on our genetics and on how vigilant we are about diet, exercise, smoking, alcohol. 
If you’re under age 40, eat a diet high in calcium-rich foods; get plenty of high-impact exercise e.g. running, jumping.
If you’re 40 or older, add a calcium-magnesium-vitamin D supplement, and do strength-training exercise in addition to impact exercise. Strength training has been shown to prevent bone loss.
.
3. MEDICATION, LONG-TERM USE
Corticosteroids (e.g. Prednisone), Thyroid hormone, and SSRI antidepressants -- are associated with bone loss.
Taking cortisone drugs over a long period of time interferes with hormone levels in a way that leaches calcium, vitamin D, and other nutrients from your bones. People who have AUTOIMMUNE DISEASES e.g. Crohn’s disease, Lupus, or Rheumatoid Arthritis have Osteoporosis at a much higher rate than the average person because of the corticosteroids used to treat these conditions.
.
4. SMOKING
Experts don’t know exactly how smoking sabotages bones, but it’s clear from numerous studies that it does...so if you’ve been a smoker throughout your life, chances are high that you’ve compromised your bones.
.
5. ALCOHOL
Alcohol is a bone-weakener; it leaches calcium, magnesium, and other minerals from your bones. The more you drink, the more likely it is that it’s happening. Women are more vulnerable to this type of bone loss than men.
.
6. CALCIUM, VITAMIN D, MAGNESIUM
Most American adults are severely D-deficient, putting them at risk for weak bones and for several types of cancer. MILK (dairy, soy or rice) that has been fortified with vitamin D, Calcium and Magnesium should be taken daily.
.
7. EATING DISORDERS
Artificially low body weight lowers hormone levels, causing skipped periods. Anything that lowers estrogen levels interferes with bone building.
.
8. (WOMEN) IRREGULAR MENSTRUATION
Low levels of estrogen are typically responsible for missed periods or a cycle that starts and stops, and low estrogen contributes directly to bone loss. Low estrogen can be caused by an eating disorder, overexercising, or polycystic ovary disease PCOS 
.
9. FAMILY HISTORY
e.g. a close relative who had osteoporosis before the age of 50 or before menopause.
Family history is a major indicator that your bones are weakening. If you come from a family where the older adults have a history of fractures, poor posture, or loss of height, chances are your family members had osteoporosis, whether or not it was ever diagnosed. And if they had it, it’s likely you do too. Compile a family health history. If you had relatives who suffered from osteoporosis, tell your doctor.
.
10. CAUCASIAN/ASIAN, FEMALE, OVER 50
Just one of these risk factors makes it more likely your bones are thinning. If all three are true for you, there’s a good chance your bones are at risk for fracture. But African-American women also have reason to be concerned. A recent study showed that low bone mass is much more common than once believed in all ethnic groups, including African-Americans.
--If you’re 60, 70, or beyond, pay even more attention. Bone-thinning risk increases with age; osteoporosis experts estimate that after the age of 75, 90% of women will suffer a fracture.