What vitamin D form? 15. February 2009 William Davis (36) In response to questions regarding why don't vitamin D tablets work, here are my observations. When I first started correcting vitamin D levels around 3 1/2 years ago, people would begin with starting 25-hydroxy vitamin D blood levels of around 20 ng/ml. Taking, say, 6000 units vitamin D as tablets over 3 months yielded blood levels of 24-30 ng/ml. Taking 6000 units in an oil-based form, and blood levels would commonly be 60-70 ng/ml. In other words, tablets are very poorly absorbed. I also saw very erratic absorption with tablets, with tremendous variation in blood levels. I witnessed this effect many times. I finally began telling patients to avoid the tablets altogether. It's simply not worth it. Taking dose X of tablets, you cannot predict what the blood level of vitamin D will be. Now, you can sometimes make the tablets get absorbed by either taking with a teaspoon of oil (e.g., olive, flaxseed) or taking with an oil-rich meal. However, I am uncertain just how consistent the absorption is under these circumstances, not having done this enough times to know. Oil-filled gelcaps are no more expensive than tablets (or perhaps a dollar more). Health food store employees and pharmacists don't know this. I have had many patients come to the office claiming they changed to tablets because that's all their health food store or pharmacy carried and the person behind the counter assured them it was the same. Blood level of vitamin D to confirm: right back down to the starting level or near it--little or no absorption. The only way to know whether a preparation is absorbed is to check a blood level. But, in my experience, having checked vitamin D blood levels thousands of times, gelcaps never fail; tablets fail over 80% of the time.