According to the last census, 84pc of the country may still be Catholic, but 269,800 see themselves as having no religion; and other surveys suggest that less than half of Catholics here attend Sunday Mass. Things have changed greatly since 1973, when 91pc attended Mass every week.
But this decline may not be solely a spiritual matter. Our lack of faith may be affecting our health and well-being. Because there's growing evidence that religious belief can be an important factor in the treatment of a number of chronic illnesses.
Last October, it was reported that prayer was one of a number of "psychological interventions" that had had a positive effect on coronary care patients in a study led by Dr Zoi Aggelopolou. For religious patients taking part in the study, nurses would help them with their prayers during their time in hospital. A follow-up survey found that patients who received these interventions were less likely to have suffered any further cardiovascular episodes.
At Wayne State University, they examined the effect of faith on traumatic brain injury (TBI). TBI is the impairment of the brain's normal functioning following a head injury. TBI victims completed a number of neuropsychological tests and interviews to assess their mental and physical abilities, as well as their level of "religious well-being." The researchers found that those who reported having "higher levels of religious well-being" had achieved better emotional and physical rehabilitation. They found that a positive health outcome could be predicted by someone's reported religious well-being.
Prayer appears to be particularly potent for those suffering from psychiatric illnesses. A study by Dr David H Rosmarin at Harvard found that those with a belief in a higher power enjoyed greater improvements during short-term psychiatric treatment.
"Belief was associated with not only improved psychological well-being, but decreases in depression and intention to self-harm," said Dr Rosmarin.
An earlier study, carried out by Rush University, looked at those diagnosed with either major depression or bipolar depression. Each patient's symptoms were assessed on admission, and again after eight weeks of treatment. It was found that those patients with strong religious beliefs had had a better response to the treatment, and in some cases were 75pc more likely to get better.
"In our study, the positive response to medication had little to do with the feeling of hope that typically accompanies spiritual belief," Dr Patricia Murphy, assistant professor of religion at Rush University, said at the time.
"It was tied specifically to the belief that a 'supreme being' cared.
'For people diagnosed with clinical depression, medication certainly plays an important role in reducing symptoms. But when treating persons diagnosed with depression, clinicians need to be aware of the role of religion in their patients' lives. It is an important resource in planning their care."
Such is the effect of religious belief on mental health, that at the annual meeting of the American Psychological Association in 2011, Dr Rosmarin encouraged mental health professionals to find out about their patients' beliefs, and to include these beliefs in their treatments for religious patients.
But faith doesn't just help with illness; there's evidence that it can improve our day-to-day mental well-being too.
At Ohio State University, they devised a novel method of studying how prayer could help those with anger issues. A number of college students were recruited and asked to complete a questionnaire to assess their levels of anger, fatigue, depression, vigour and tension.
The students were then asked to write an essay about an event in their lives that had made them feel angry. They were told that the essay would be evaluated by an unseen partner. However, all the essays were given the same negative evaluation and included the phrase, "This is one of the worst essays I have ever read!" Basically, this part of the experiment was about making the students angry.
"The effects we found in these experiments were quite large, which suggests that prayer may really be an effective way to calm anger and aggression," said Brad Bushman, professor of communication and psychology at the university.
While many of these studies focused on the health effects of Christian beliefs, similar effects have been found with other religious faiths. For example, a study in Saudi Arabia found that faith in Allah could help women cope with breast cancer treatment.
And research by the University of Missouri found that spirituality, regardless of religion, was enough to help in the rehabilitation of physical and mental health. The researchers looked at Buddhists, Muslims, Jews, Catholics and Protestants, and found that all experienced positive mental health effects attributable to their faith.