iText: PdfTable cell vertical alignment

I'm trying to vertical align my headet cell text to be in the middle of the cell height.

This is my code:

    PdfPCell c1 = new PdfPCell(cerate_phrase("" ,regular_bold ));
    c1.setHorizontalAlignment(Element.ALIGN_CENTER);
    c1.setVerticalAlignment(Element.ALIGN_MIDDLE);
    c1.setBackgroundColor(BaseColor.LIGHT_GRAY);
    table_.addCell(c1);

but this does not work. setHorizontalAlignment is centered but not setVerticalAlignment.

Am I doing something wrong? how can i vertically align it in the middle?

Any help will be appreciated.