Does atheism make you happy?

Remember the ad.  'There's probably no God.  Now stop worrying and enjoy your life.'  A lot was made of the fact that they used the term 'probably' but then it is impossible to prove the non-existence of God.  However, it is not the 'probably' I want to contend with.  It is the implication that we all would be happier without religion.  That is simply not true.  Professor Andrew Simms, former President of the Royal College of Psychiatrists, comments that

The advantageous effect of religious belief and spirituality on mental and physical health is one of the best-kept secrets in psychiatry and medicine generally.  If the findings of the huge volume of research on this topic had gone in the opposite direction and it had been found that religion damages your mental health, it would have been front-page news in every newspaper in the land.