It’s fat soluble vitamins, so you need to have fat in a fish in order to get vitamin D. 

So all fatty fish such as salmon and mackerel are very good.

John -   If you take very large volumes or quantities of vitamin D, you'll get hypercalcaemia and that can have adverse effects and indeed can cause kidney failure if you really overdo it. 

But as George was saying, in fact, it’s very hard to get anywhere near those levels.  You have to really work quite hard at it and for the general population, the sort of supplements that we will get from our diet and from adding a tablet of vitamin D to our routine is not going to take you anywhere near that level.

George:: I agree.  The safety here has been demonstrated in volunteers.  So, the institute of medicine’s recommendation was up to 4,000 units a day for adults.

The safety factor is huge so that volunteers have been given over 100,000 units a day when it’s been gradually increased over time, which is you know, let’s say 25 times the Institute of  medicine maximum recommendation and no ill-effects were seen. 

So if you increase the amount of water you took a day by 25-fold, then it would be fatal, but you can increase the amount of vitamin D slowly and in fact, no side effects have been found.  I'm not recommending people to take that, but there's a big safety factor.

Elina -   Skin colouration is the most important personal characteristics which is affecting how likely you are to be Vitamin D deficient or how efficiently you can produce vitamin D by your skin. 

So for example, we were looking at this cohort of 45-year-old individuals and if among the white skinned individuals, we had less than 10% who were severely vitamin D deficient, so that by severe, I mean people who were at increased risk of rickets or bone deformities.  In individuals who were from non-Caucasian ethnic groups there was 40% of them.  So it’s a massively strong risk factor for vitamin D deficiency.

Chris -   What about the other cultural aspect of this, people who are not necessarily very darkly skinned, but choose to cover themselves from head to foot in very dark fabrics so they don't see the sun?  What about that practice?

Elina -   Yeah, that's of course is a combination of different things and you can't produce vitamin D by your skin without exposing some of your skin to the sunlight.

Chris -   So, what should people who are in these risk groups do?  Should they go and get a vitamin D test then?

John -   Yes, I think you raised the very important point of the additional cultural burden of concealment if you like from the sun which of course means that particularly, families of Muslim extraction are at increased risk, and clearly, the common sense thing is to add a dietary supplement of vitamin D – it’s very straightforward.  But I think it’s also worth just generally picking up this point about our evolution. 

It’s very clear that as we migrated out of Africa, we got paler the further north we went and that had to have been a Darwinian selection process and almost certainly, now that we know so much about vitamin D, the strong argument is that as we got further away from the equator, we had to get paler to remain healthy because our vitamin D levels were at risk.  So, I think that both in terms of the genetic predisposition if you like to vitamin D problems and the cultural problems being that anyone from ethnic minorities should think very seriously about taking a vitamin D supplement.

Well I think there are a variety of different kinds of light boxes, but I think just light unless it’s got an awful lot of radiation, it’s not going to generate any vitamin D so that I mean, people can go to – you know, they go to tanning salons and so forth and that will in fact generate vitamin D, but the downside of this of course is it may have the consequences of being exposed to sun. 

So, the way around the dilemma, it seems to be, is if you want to increase your vitamin D content, then just simply take it by mouth as a regular vitamin D3.

Not unless your window is open.  Window glass does block the UVB radiation.

I think that everything needs to be considered in a balance and there is a very good reason why sunblocks are recommended but common sense should be applied in using those as well. 

I don't put the sunblock on before I go outside but I go first outside and only after being there for 10 or 15 minutes I apply the sunblock. I allow both some vitamin D synthesis in the skin as well as protecting myself from any excess in sunlight.

I think the answer is yes, it is an acceptable alternative. 

The fact is, it is very difficult in our modern world to persuade people to get out into the sunshine.  I mean, that is the best thing to do to get out into the fresh air, get exercise, as well as getting sun exposure, and obviously, that's going to affect things like obesity and so on. 

But the reality is that especially in the winter months in the northern climbs, you're still not going to get enough vitamin D from that source, so you really have to take a supplement unless you have a diet that is very rich in oily fish which would give you a natural supply.

George -  Well chemically, it’s a very simple molecule and it’s identical really to what you make in your skin, so I don't think there's any reason to think that it would be any different. 

But I think the issue of supplementing the population is awkward.

Despite the fact there's a control study showing that folate prevents neural tube defects, it’s not added to the food and one can only compare what happened in America now.

I'm a Canadian, but I’d have to say, the way they dealt with this was the way it probably should’ve been done which is that they supplemented their food within a couple of years that the results coming available and they were able to show that as much as 80% of neural tube defects were prevented. 

Here, I think these issues have been more controversial and just the fact that people want to put supplements then doesn’t mean that it’s bad.  There are lots of examples where supplementation is very useful.  Iodine and salt is a good example.  No one argues about that and I think in a few years, nobody is going to be arguing about this as well.