In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: High doses of vitamin D are known to cause calcification of the artery media in as little as 3 to 4 days .
### Output Text:
High doses of <span class="chemical">vitamin D</span> are known to cause calcification of the artery media in as little as 3 to 4 days . 