Bone density is also known as Bone Mineral Density (BMD). It is the best way to measure your bone health. BMD is the quantity of bone mineral in bone tissue and may be defined as mass of bone mineral per volume of bone. It is measured by proxy according to optical density per cm2 of bone surface upon imagination.
Low BMD means you have "Porous bones" and at high risk of osteoporosis and fracture. Generally, old age people are at high risk of low BMD. To avoid this condition, you should have balanced diet and add calcium and Vitamin-D supplements in your diet. Normal healthy people have their T-score between +1 and -1.
How to improve bone density ?
Weight lifting and strength training exercises are helpful in improving low bone density. Eating diet rich in Vitamin-K will reduce calcium loss and helps in mineral binding to the bones. You should avoid smoking and alcohol. Cashews are super nuts for good BMD. Estrogens and testosterone therapies are also helpful for maintaining healthy bone density.