We can see here experience from the USA, tests funded by Medicade. We are looking at not all blood tests but those concerned with immunology and nutrition. In the year 2000 vitamin D testing was bottom of the list, but since then the increase in number of tests has been enormous.
The question is whether this is just a new fad or whether it is of clinical importance. Low blood levels of vitamin D have been linked to a variety of diseases including coronary heart disease, stroke, diabetes, Crohn's disease, rheumatoid arthritis, breast cancer, colon cancer, prostate cancer, multiple sclerosis, and above all early death. It would appear therefore that to identify and correct low blood levels of vitamin D would seem to be sensible, even thought the benefits in the long term are not yet clear.
The extent of vitamin D deficiency is far greater than anticipated. It is more common in northern Europe than in southern Europe, similarly in France and the UK. Locations with the lowest levels have the worst health. The majority of people appear to have low levels of vitamin D, especially Asian and Black ethnic minorities in the UK and the USA.
It is necessary note that unfortunately there are two units of measurement in use, nanogrammes per ml and nanomols per litre. When you receive your result it is essential to know which of the two measurement unit are being used. The ideal levels are shown here, but very few people achieve these levels naturally.
Most vitamin D comes from the action of the sun on the skin, and few people achieve adequate sun exposure as judged by vitamin D levels in the blood. Air conditioning in hot countries makes this worse on an international scale as industrialisation expands, people spending more times indoors. It is necessary to eat a great deal of fish each day to achieve a good vitamin D level by diet. Sun-bed use leads to good levels of vitamin D and sun-beds used without sunburn are not dangerous to adults.
If vitamin D deficiency is so common it could be argued that we should all take a supplement without blood testing. This is safe with a supplement of 2000 units per day. "Overdose" of vitamin D is extremely rare and does not occur if exposure to the sun is good as the sun acting on the sun appears to de-activate circulating vitamin D. It will occur if calcium is given with vitamin D and it is not necessary.
We can see that with supplement, in this case 20,000 units each week, the blood level does not keep increasing. It rises into the ideal range and then it stabilises. Vitamin D is consumed by the body, it is utilised and then inactivated. The supplement dose that achieves a steady state is obviously the amount that the body requires each day.
We can also see that although multiple measurements were performed on this particular subject, experience now tells us that if the ideal range is achieved after three months that will become the steady state.
Although the blood testing of vitamin D is increasing, many people who are at risk of vitamin D deficiency are still not being tested. We can anticipate that the number of tests will increase. Perhaps vitamin D testing should be part of routine testing in early pregnancy, as if a child starts life with a good level of vitamin D, it is likely to continue through life. It appears to be that vitamin D is most important in the early stages of life, particularly before birth and shortly after.