My blood test showed a vitamin d level of 17. the doc prescribed ergocalcitrol 50000 iu. is this low level common? how can i prevent it in the future?

Yes. Get sensible sun: Low vitamin d concentrations such as those described are very common in the us population. They are especially common in persons who are homebound, drink little vitamin d fortified milk, and or have darker skin color. The best way to prevent low vitamin d is to take a multivitamin, drink vitamin d fortified milk, and to get 10 to 15 minutes of sensible sun exposure daily during the summer months. This means exposing at least your arms and legs 10 to 15 minutes prior to putting on sunscreen.