D is unique among nutrients in that it can be obtained simply through exposure to a certain spectrum of ultra violet light, as is produced from sun exposure. What happens here is that cholesterol in the skin is enzymatically converted into D. It takes about 15 minutes of UV exposure to produce about 10,000 units of D in the body. But some people are concerned about even this small level of sun exposure, mainly because of admonitions from doctors about the risks of acquiring skin cancer. The other problem with this is that during the Winter, some places just don't get enough sun exposure, so you would then have to depend on food sources. Good luck with that, since good natural food sources of D are far and few between. The obvious solution to this problem is to ingest vitamin D supplements.
Recently, an "expert" science panel concluded that vitamin D supplements are superfluous, and probably dangerous, since most people show normal levels of activated D in their blood. But what these scientists considered an optimal blood level of D differed from that offered by other scientists more versed in vitamin D research. According to the latter group, most people are likley deficient in the optimal blood levels of activated D, and should take a D supplement.
That's the next controversy about D: which type of D is best? D comes in two forms, D3 and D2, with the latter being synthetic, produced as a result of irradiating sheep wool. For years, experts always advised people to stick to the natural (D3) form, noting that it's retained longer in the body compared to the synthetic D2 version. But others noted that the biological activity of D2 had been adjusted in terms of units per dose to match that of the natural form of D, or D3. One study even directly compared the two forms of D, with the conclusion being that they were biologically equal.
In a new study, however, which again compared the two forms of D head to head, D3 again proved superior. This study involved 33 healthy adults, who were given D at a dose of 50,000 units a week for 12 weeks. The results showed that natural D3 was about 87% more potent compared to D2 in raising activated D levels in the blood, and also showed 2-3 times greater storage in the body than the same dose of D2. As such, D3 is the best form of D supplement to use. This however, is a moot point, since I've never seen a stand-alone D2 supplement, although it's often the form used in vitamin-mineral supplements, and in milk. As for the dose, most experts suggest that 2,000 units a day is a good start. But to be precise, it would be better to take a baseline blood test for the activated D form. Good levels start at 30 or higher, with about 50 being optimal. Those who are old, fat, or have darker skin, may need to ingest higher levels of D to reach the optimal level.
Heaney, RP, et al, Vitamin D3 is more potent than Vitamin D2 in humans.J Clin Endocrin Metab 2010: in press.
©,2015 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited
