Restrict Direct Acces To Options-general.php?page=user-advertising

Hi there!

I created a menu only for supporters too see:

<?php global $user_ID; if( $user_ID ) : ?>
<?php if( is_supporter()) : ?>
<?php add_dashboard_page(__('Adsharing','menu-test'), __('Adsharing','menu-test'),
'manage_options', 'options-general.php?page=user-advertising'); ?>
<?php else : ?>
<?php endif; ?>
<?php endif; ?>

But now I would like that non supporters don’t have acces too ‘options-general.php?page=user-advertising’, so that they get redirected to let’s say index.php when they type in the URL in the browser adresbar.

How could this be done?