It depends: It depends why one has weak bones: frail or fragile bones are usually due to osteoporosis (and sometimes due to genetic disorders such as osteogesesis imperfect, and secondary to cancer, metastasis). Week bones due to osteoporosis: usually secondary to postmenopausal status (sex-hormone deficiency), age, or due to other medical disorders. It is very important to identify and treat the latter be.
Vitamin d def. Possible vitamin d deficiency.
Usually not. Osteoporosis is a common problem for postmenopausal women, not genetic. Longstanding hyperparathyroidism can also lead to bone calcium loss (generally caused by a benign tumor of a parathyroid gland). Metastatic cancers to bones can lead to pathologic fractures. Best to review with your doctor to assess risk factors, and there are tests to evaluate bone health.