Add Categories For a Post As Class Names On The Body Tag - Wordpress

Categories As Body Class Names

// add category nicenames in body and post class
function category_id_class($classes) {
  global $post;
	foreach((get_the_category($post->ID)) as $category)
		$classes[] = $category->category_nicename;
	return $classes;
}
add_filter('post_class', 'category_id_class');
add_filter('body_class', 'category_id_class');