Function to add category nicenames to body class

gistfile1.php

<?php 

add_filter( 'body_class', 'tax_body_class' );
/**
 * This function adds category nicenames to body class.
 * 
 * @access public
 * @author Remkus de Vries
 * @param mixed $classes
 * @return void
 */
function tax_body_class( $classes ) {
	
	if ( is_singular('post') || is_category() ) {
	
	global $post;
	
	$terms = get_the_terms( $post->ID, 'category' );
	
		if ( $terms && ! is_wp_error( $terms ) ) {
		
			foreach ( $terms as $term ) {
				
				// assign body class for the blog categories
	
		    			$classes[] =$term->slug;
		    		
	
			}
		}
	
	} 
	
	return $classes;
	
}