What are they trying to do. They are trying to make it all unintimidating and simple. Certainly 5 k a day does that. What am I trying to do. I am trying to optimize my vitamin D level and believe this can only be done if weight is taken into consideration. Now a little story about me and it applies to you also. It is all about optimization and dosing.
I have been taking "varying" doses of vitamin D since 2004 in attempt to lean by experience and optimize too. From time to time I have stopped vitamin D and had a blood level drawn. I drew the blood levels when I started to feel significant pain. I had a significant pain increase when my blood level was 75ng. ( Yes Virginia, vitamin D is a significant ant inflammatory and therefore pain reliever. It is so slow on you may not notice the improvement until you try going without it. All of a sudden you hurt badly. Do you suppose it has something do with running out of vitamin D a few days ago. You betcha! It is nice to keep a extra bottle on hand). I digress. My optimization means, to me, about a level of 90 ng. I seemed to end up with a 90 when taking 10 to 9 k the last few years. But, in the last few years I have stopped my vitamin D a few times to see what my pain level was and in the process depleted my fat stores of the vitamin.
So I was taking 9k and I had a blood level of 120ng. To much but not dangerous. Toxicity occurs at something over 200 ng. I had been taking that dose without reducing it for easily two years. So I cut my dose down to 5 k. ( Note: as your blood level goes up it takes more vitamin D to achieve the same movement upward that occurs when your blood level is low. What I mean is if your blood level is 30 typically your blood level will go to 40 with a 1k increase in vitamin D a day. At a blood level of 90ng a 1000 increase in vitamin D will bring your blood level up 2ng. So it depends).
I checked my blood level again six months later and my blood level was now 102 ng. I was not alarmed, but do not believe that level is needed so I have now cut my dose down to a tad over 4k a day. I expect that it will drop into the low 90's. Right where I want it to be. I can test in three months and find out. Recall that it takes 3 months for your level to stabilize after changing your dose assuming you take the same amount every day. So what happened here. Recall that vitamin D is a fat soluble vitamin. It took awhile to get into the fat and fully saturate it. At that point, once saturated, you blood level will rise because there is no other place for it to go....
How does this work. Your body is made up of three compartments that can absorb a fat soluble vitamin. These compartments are the blood, the cells of the body and the fat of the body. Vitamin D most easily goes into the blood then the cells from the blood and lastly a little goes into the fat and is stored there. Just like any storage place, once it is full the spillage will be outside. Outside in this case will be represented by the cells and blood with a corresponding increase in blood level.
Bottom line. You need to test and you need to test at least once a year. Also if your level is like mine it will take a significant cut in vitamin D to bring it back into the proper range. In my case a cut of 1000 iu when I was taking 9 k a day would have ended up with a drop of perhaps only one or two ng!
I do not know of anything bad that will happen with a level of 120 or even more, but why take more than is needed or recommended by anyone. As to the last statement, there are Doctors that recommend up to 100 ng for those who are ill or vulnerable. At my age, almost 74, I would like to continue to do well. Stay tuned.
Don't forget vitamin D utilizes magnesium so you need to supplement that also. Vitamin K2 directs calcium to the proper place ( bones and not the heart) and helps with the proper utilization of vitamin D. Calcium lining the coronary arteries is the leading indicator of a pending heart attack. Not cholesterol. Suppose those recommending statins will change to vitamin k? Not likely! And as a final reminder vitamin k will change the effectiveness of those on blood thinners such as Coumadin. Don't take vitamin k in such a case without the Doctors monitoring.