Menu Bar Layout Question - How to stop it bumping other content down the page

I have a vertical menu bar linking to an A-Z list of items running down the side of a page as quick links to other content. Unfortunately because the list is long, it is bumping content from the next section downwards (including when I float the menu bar).

Does anyone have a genius idea how I may be able to stop this happening? You can see an example here: http://drgeraldlewis.com/disease-information/disease-alzheimers/

Thanks