Source

File: wp-includes/class-wp-user.php

public function update_user_level_from_caps() {
		global $wpdb;
		$this->user_level = array_reduce( array_keys( $this->allcaps ), array( $this, 'level_reduction' ), 0 );
		update_user_meta( $this->ID, $wpdb->get_blog_prefix() . 'user_level', $this->user_level );
	}