NZer1 wrote:Ed can you help me understand some thing please.
What is Vit D deficiency?
What is illness created hi use of Vit D?
Do the people with deficiency in Vit D actually have intake but not able to metabolise it?
I'm confused by the terms and head off with thoughts that maybe wrong at the start.
Nigel
I think the broad answer to the question of what is vitamin D deficiency is that it is having less than the body requires. The specific level likely is very individual and depends on the rate at which you make or take vitamin D as well as on the rate that it is used by the body.
The only numbers we know for certain is that levels of less than 30 nmol/l (12 ng/ml) will cause rickets in children or ostemalacia, the adult form of rickets. It is simply too little to build and maintain bone health.
We have a reference in this thread which shows that it appears that vitamin D is being consumed at a high rate by people with MS as they go from having no signs of the disease through CIS and on to frank, clinically definite MS.
Another way of looking at this is to look at the vitamin D levels of people living near the equator who are to some degree, representative of our evolutionary past. Solar exposure below the 32nd parallel where you receive UV-B radiation year around provides on average 10,000 IU - 20,000 IU a day and results in, depending on skin pigmentation, levels that are over 200 nmol/l (80 ng/ml), but generally not much higher than 225 nmol/l (90 ng/ml).
So the definitive answer to the question of what level constitutes deficiency is that it is somewhere between 30 nmol/l (12 ng/ml) and 200 nmol/l (80 ng/ml).
I think your second question is what happens if you have too much vitamin D, high levels. The answer is that you screw up the management of calcium levels in the body. That has very serious effects. It can result in the body taking in too much calcium from the diet and causing calcification of our organs, effectively turning your kidneys into bone, along with the heart and other organs. Paradoxically, it can also cause the body to attempt to sequester calcium to the point that it starts breaking down bone to obtain more and in that process, releases toxic levels of phosphate, one of the other components of bones.
Levels that cause this to happen, again, probably varying individual to individual, but are certainly north of 225 nmol/l (90 ng/ml). It is virtually impossible for this to happen if the source of vitamin D is solar exposure because of mechanism in the skin that limit the production of vitamin D to generally not more than 20,000 IU/day, although if more is needed as we know is the case in pregnancy and during periods of bone growth, the body will allow more than 20,000 IU/day to be made. The mechanism that regulates this isn't so much looking at how much is being made as how much is required based on the rate at which it is being used up.
If you took high levels of vitamin D as a supplement, the answer depends to a large degree on how you take it. Taking high levels daily can trigger hypercalcemia, but taking the same daily amount in pulses once or twice a week will generally avoid it because those much higher pulses cause parathyroid hormone (PTH) levels to drop which lowers the rate of absorption of calcium from the diet as well as blocks attempts to resorp calcium from the bones.
Your third question relates to whether there can be problems with the metabolism of vitamin D that in spite of intake results in a deficiency.
Yes, that can happen and it is a known factor in some diseases, now fairly well documented in the case of children who become diabetic. Genetic findings show that the most common genetic variations in these children are ones related to the processing of vitamin D.
There are a lot of genes involved in vitamin D processing. Ones that convert various forms in the liver. Ones that do the conversions necessary in the kidneys. Ones that transport these various forms to and from the liver and kidneys. Ones that break down or create various forms elsewhere in the body.
Some level of variation in these genes can cause the body to be unable to create or convert various forms of vitamin D so you can certainly have problems in maintaining vitamin D levels in spite of high intake of vitamin D.
So the full answer is that you can have inadequate levels of vitamin D even with relatively high intake or solar production of vitamin D both as a result of high rates of use of vitamin D in conditions which likely are involved in MS or other diseases such as diabetes, Crohn's Disease, Rheumatoid Arthritis and so on as well as from genetic variations that impair the processing of vitamin D.
The answer to all your questions about vitamin D in 150 words, more or less.
All this is very much more nuanced then I have made it here and it is all subject to continued study that may prove some of this wrong or irrelevant.
The good news is that it seems the whole biomedical field is doing nothing but studying vitamin D these days. I have alerts set up to let me know about new studies on aspects of vitamin D and am getting notices of over 100 a day. Last time I looked at this, there had been over 3,500 new studies uploaded to the US NIH PubMed in the previous 12 months.
The US clinical trials monitoring group,
http://www.clinicaltrials.gov reports over 1,200 trials involving vitamin D of which there are 22 looking at the relationship between vitamin D and MS.
These are simply unprecedented levels of research so we will likely soon know much more about this.
One final point. I think it is fair to say that evolutionary history tells us that the body has evolved to make use of abundant resources such as the air we breath, water we drink and the sun light we expose our bodies to. We use iron and zinc which are relatively abundant, rather than gold and platinum.
One additional "final" point. The farther you are away from equator, the less UV-B radiation you get and the lower the amount of vitamin D your body can produce from this source. There are not a lot of dietary sources of vitamin D and few people in the world consume enough of them to maintain adequate levels of vitamin D. Just to get 1,000 IU you would need to eat roughly 1 kg of wild salmon a day. You can of course, get some highly concentrated dietary sources such as cod liver oil, but again, you need to consume an awful lot of it to have high intake levels.