Since laughter does effect the body, mind and spirit，the only thing you have to do to lead a happy life is laugh.
effect在此为动词，does effect为强调形式。不过这里effect似乎应该用affect。you have to do to lead a happy life为定语从句，修饰the only thing。一个句子用十个谓语动词也不奇怪，为什么就不能用二个谓语动词呢？关键是你要分析主句和从句，而不是数几个谓语动词。
