php - Impact of Share Button on Web Page Performance -

on few websites maintain, noticed adding share button addthis page varyingly slows down page loading, significantly.

what explanation , can done keep share buttons while not incurring page loading performance penalty this?

add script call bottom of page, that's do, right on top of </body>.

...  html  ... <!-- addthis button begin --> <div class="addthis_toolbox addthis_default_style "> <a href="http://www.addthis.com/bookmark.php?v=250&amp;username=xa-4d4c6a9028bcda9b" class="addthis_button_compact">share</a> <span class="addthis_separator">|</span> <a class="addthis_button_preferred_1"></a> <a class="addthis_button_preferred_2"></a> <a class="addthis_button_preferred_3"></a> <a class="addthis_button_preferred_4"></a> </div> <!-- addthis button end --> ...  html  ... <script type="text/javascript" src="http://s7.addthis.com/js/250/addthis_widget.js#username=xa-4d4c6a9028bcda9b"></script> </body> </html> 

edit: moving script call bottom of page page load before script , users not feel impact.