Dr. Daniel McCartney:

Absolutely. There is good research behind that which suggests that melatonin is suppressed by the exposure of the back of the eye, the retina, to that white light. It is very well established that the physiological response to that white light is responsible for some of those better outcomes in persons with SAD.

I would like to follow up on a number of questions or issues raised in summation. Deputy Seán Crowe raised the issue of opting in. Under the UK scheme, even though, in theory, vitamin D supplementation is being provided free to 2.7 million of the UK's most vulnerable citizens, it is being provided on an opt-in basis. That is an example we should not follow. It must be operated on an opt-out basis if we want supplementation to be effective for vulnerable groups, such as people in nursing homes, our black and minority ethnicity, BAME, communities, our front-line healthcare professionals and people arriving to test centres. We cannot rely on people having the knowledge to know that they need vitamin D and to take the appropriate action. It needs to be provided on an opt-out basis.

The other issue I will raise is that we have borrowed a lot of the guidance from the UK in this area and a lot of the evidence our statutory agencies have reviewed in this regard has also been from the UK. That evidence has focused on musculoskeletal health. It is really important that the committee understand that the thresholds for blood vitamin D that must be achieved for some of these skeletal benefits are much lower than those to be achieved for immunological function, including for defence against Covid-19.

Were NPHET to review this evidence, we would need a specific review of the evidence on immunological health as it centres on Covid-19. Reviewing the evidence of vitamin D in respect of musculoskeletal health does not bring us any further along.

The other thing to realise here in the context of that information is that the randomised control trials that many people have requested and that we would all like to see in this area may never happen. Professor Kenny will say that the biggest of those studies is in Córdoba in Spain where some 1,000 individuals have been targeted. They are on 300 at the moment after the elapsing of nine months in that study and may never reach the 1,000 patients.

We cannot wait for those randomised control trials. There is a model or paradigm called the Bradford Hill criteria for causality and the evidence that we have in relation to vitamin D and Covid-19 already meets those Bradford Hill criteria. These are the same criteria that anti-smoking interventions have been based on, which as we said earlier have been very effective.

Finally, on the issue of our population, we mentioned obesity. Obesity affects approximately 60% of our adult population, who are either overweight or obese. The dosage of vitamin D one requires if one is overweight, that is a body mass index, BMI, of between 25 and 30, is about one and a half times what a person of ideal weight would require to raise their blood levels by the equivalent amount. When one gets into the obese category, that is a BMI above 30, then one may be looking at a dosage of about two to three times to achieve the equivalent level of increase in the blood. Even though 20 to 25 mcg per day may be sufficient for most of the adult population to reach the required threshold for immunity against Covid-19, there is a significant proportion of the population who will require supplementation at higher doses than this, including people with darker skin, our nursing home residents, older adults, and some other vulnerable groups old as well.

That is all I really have to say but as a group we will be delighted to engage with NPHET if that opportunity arises and to furnish the committee with any further information that they require on any of the issues that we discussed today.