In 1994, the World Health Organization (WHO) defined the term osteopenia. Before 1994 this medical term did not exist and many people confused this with osteoporosis; even though osteopenia is not a disease like osteoporosis.
Osteopenia is a stage of bone loss before osteoporosis, but having this classification on a DXA, does not mean it will develop into osteoporosis for all.
Osteopenia is a bone mineral density measurement that is below the average for bone loss. As we age, it is normal to lose some bone. 
The WHO Definition for Bone Loss
Normal Bone Density
Any score above -1.0
Any score between -1.0 and -2.5
Any score below -2.5
The World Health Organization went on to further classify established (severe) osteoporosis as a score below -2.5 with a non-traumatic fracture. 
- Family history of bone loss
- Race (Caucasian and Asians are at highest risk)
- Weight and eating disorders
- Malnutrition and Malabsorption disorders
- Radiation or chemotherapy exposure
- Age 
To see a full list of causes for osteopenia read the National Osteoporosis Foundation site on bone loss causes.
Since osteopenia is a silent disorder, you need to have a dual-energy X-ray absorptiometry (DXA) scan to measure your bone mineral density.
Since osteopenia is not a disease, some physicians feel it should not be treated the same way as osteoporosis due to the long term effects of some of the osteoporosis drugs.
If your physician feels that osteoporosis drugs are not suitable for osteopenia, they generally recommend, lifestyle changes like weight bearing and muscle strengthening exercises and healthy diet with adequate amounts of calcium and vitamin D.
If your physician recommends osteoporosis medications, here's a list of available drugs:
- Bisphosphonates: Actonel®,Atelvia® (time-released), Boniva® (tablet and quarterly injection) Fosamax®, Reclast® (infusion-yearly and biannual).
- Anabolic: Forteo®, daily injection for 2 years.
- SERMs: Evista®
- HRT: ET (estrogen therapy) and HT (hormone therapy)
- Biologics: Prolia® twice yearly injection for those at high-risk of fracture
- Salmon Calcitonin: Injectable and nasal spray
- ®: Medicinal food, requires doctors prescription
- Strontium Ranelate®**: Available in the European Union only
Just keep in mind that you need to agree with your treatment plan, and if you want to try diet, exercise and supplements instead of medications, be sure to explain this to your doctor and come to a mutual agreement.
Some of the medications above, are not approved for osteopenia, e.g. Forteo and Prolia.
- National Osteoporosis Foundation 2011 _http://www.nof.org/ _
- World Health Organizations T-score definitions 2011 _http://courses.washington.edu/bonephys/opbmd.html _
- History of Osteopenia, eHow.com 2011, _http://www.ehow.com/about_5348403_history-osteopenia.html _