public function isEmailTaken($email)
    {
        $query = "SELECT count(*) FROM {$this->config->table_users} WHERE email = :email";
        $query_prepared = $this->dbh->prepare($query);
        $query_prepared->execute(['email' => $email]);

        if ($query_prepared->fetchColumn() == 0) {
            return false;
        }

        return true;
    }