<prompt> What is the World Health Organization WHO definition of osteoporosis?Bone mineral density less than 1 standard deviation below the mean of a young, healthy adult.Bone mineral density at least 2.5 standard deviations below the mean of a young, healthy adult.T score less than -2.5.B and C.  <response>: Ans. D. B and C.In 1994, the WHO introduced definitions for osteoporosis and osteopenia in terms of T score thresholds of -2.5 and -1 respectively. A T score of -2.5 means that the bone mineral density in the lumbar spine L2-L4 is at least 2.5 standard deviations below the mean of a young age 25-35, healthy female. A T score of more than -2.5 implies it is more positive and hence could represent either osteopenia or normal bone density. 