Osteopenia is the condition in which bone density is somewhat less than a “standard” young person of the same sex. It is not a true diagnosis, nor is it a disease; it is simply a state of relatively low bone mass.
The causes are not always related to bone loss; if you never developed a high peak bone mass during your youth, you could have lifelong osteopenia. Similarly, if you are not a young person, you will not be likely to have the same bone mass as somebody who is young.
Low bone density is one risk factor for osteoporotic fracture; however, having osteopenia doesn’t mean you will have a fracture. In fact, studies suggest that well over half of those who suffer a low-trauma “osteoporotic” fracture do not have an osteoporotic bone density; rather they have “osteopenia” or even normal bone density. There is much more involved in the equation.
While childhood and adolescence are the best times to build strong bones, there are ways to halt and even somewhat reverse bone loss in adulthood. Contrary to what you might have heard, calcium is not a panacea. There are many other nutrients that play a role in bone health and, in fact, the societies with the highest calcium intakes also have the highest rates of osteoporosis.