In the discussion about the benefits of vitamin D, I notice two general difficulties: First, the general misunderstanding that if some thing is good than a lot of it is even better. This is wrong and potentially dangerous. The second difficulty is to establish how much is good and how much more is too much. With this comes the obvious question, does a sufficient amount make a difference in eczema? And here I fully agree with Spanish Key, we just don’t know for sure. Of course, we all need vitamin D to function, it is important for our immune system. But should we supplement? And if so, how much?
The review recommended by Spanish Key  explains nicely the basics of vitamin D production and function in the body and compares several studies that address the relationship between vitamin D and eczema. As you probably know, vitamin D is produced in the skin when exposed to sun light (UVB radiation) or can be ingested through vitamin D rich foods (like e.g. fish oil). As I understand, the best and worst way to get vitamin D is through sun light: it is best, because the UVB radiation sets off a self-regulating process that prevents too much vitamin D to be produced; but it is the worst, too, because of the known cancerous side effects of sun exposure. So, the art is to get enough sun exposure to produce enough vitamin D, but not as much as to out-weight the risk for skin cancer. On the other hand, ingested vitamin D is probably a good option, but if the amount is too much, it can lead to a number of complications (e.g. calcification, kidney problems). To make things a little easier, the amount of vitamin D in the body can be determined by measuring the amount of 25-hydroxy-D (25 HO D), which is produced in the liver out of vitamin D, in the blood serum. In the US a concentration below 30 ng/ml of 25-OH-D is considered deficient, in Germany the threshold is 20 ng/ml. This doesn’t seem so high, but I managed to be tested deficient! Considering that I am not working night-shifts, and like to spend time outside, vitamin D deficiency seems to be not that difficult to achieve (at least not in Germany which is about as far north as Calgary, Canada). So, I certainly need to supplement. And if I am deficient, I wouldn’t be surprised if our son J. is low in vitamin D, too. I am waiting for our doctor’s appointment to discuss supplementation with him. However, I still don’t know what is a good range of vitamin D level. Deficient means, that the lag of vitamin D can cause health problems, but what amount of vitamin D has all the benefits?
And what about vitamin D and eczema? Does it really help? I am sure that a vitamin D deficiency is bad in any case. But the question if supplementation of vitamin D helps against eczema seems to be really tricky. The main problem I see is, that it is so very difficult to conduct a good and clear study. As anyone working in research knows, the design of a good experiment and the evaluation of the data are entirely non trivial, especially in human “field-research”, on which the majority of studies about vitamin D is based. One just doesn’t have laboratory conditions where one could control for everything and then see the effect of vitamin D clearly. In Germany, for example, measuring the vitamin D level is not even a standard test and it is not covered by the insurance. The test is not done on a regular basis, which means that there is not a large database to draw from. Unfortunately, I didn’t have time this week to look at some of the cited studies in this review  to understand better the claimed results. I am always skeptic when I see studies claiming opposite results. One study could be wrong, or the effect in both studies is so small that any choice of statistics could lead to any desired outcome…. Well I will keep reading as much as possible, and see what comes along….
You might also be interested in my post about Fall children and vitamin D.