[9급 지방직 영어 2015년 14번]

A growing number of people are seeking medical attention for vitamin D deficiency, a common condition among those who spend a lot of time indoors. It is well known that vitamin D deficiency can affect one's muscles, bones and immunity and is even associated with cancer. Vitamin D is produced by the body in response to skin being exposed to sunlight. A lot of women, however, wear sunscreen before they go out, and this often makes it more difficult for their body to produce vitamin D ― as ___________________________.