Is it true that osteoporosis is an endocrine disorder?

Sometimes: Some, but not all cases of osteoporosis are associated with gland problems: too much thyroid or parathyroid hormones from those glands; the adrenal gland putting out excess cortisone; the pituitary (master gland) can also increase some of these hormones.

Yes: Although osteoporosis can be managed by many subspecialties (endocrinology, rheumatology, orthopedics, gynecology, geriatrics, bone metabolism is regulated by several hormones, therefore it is an endocrine disorder.