Final answer:
The risk factor for susceptibility to osteomalacia is taking vitamin D supplements.
Step-by-step explanation:
Osteomalacia is a condition characterized by the softening and weakening of the bones, typically due to a deficiency in vitamin D and/or calcium. In the given options, the most relevant risk factor for susceptibility to osteomalacia is option d, taking vitamin D supplements. Vitamin D plays a crucial role in the absorption and utilization of calcium in the body, and its deficiency can lead to impaired bone health.