The Count is back
I thought I’d revisit this topic, as I’ve come to some new insights on vitamin D. As a result, I have increased my daily intake to a total of 10,000 IU per day. I estimate how much I’m getting from Sun exposure and take supplements so that I get the 10,000 IU per day on average. I believe that this is the right thing to do for a number of reasons:
1) 10,000 IU/day is what you would naturally get from sun exposure if you lived as our recent ancestors. Dynamical equilbrium is reached between vitamin D production and destruction within half an hour or so, if you are in the tropics at this level. So, if you are outside for some hours every day, then you are guaranteed to get this dose on the long term. Your calcidiol levels will be approximately 220 nmol/l. To get significantly lower calcidiol levels, you woud have to get significantly less vitamin D over a prolonged period of time, which is unnatural if you live in the tropics as our recent ancestors
However, if you lived in Ice age Europe, you would not get the 10,000 IU per day after the start of Fall. Your vitamin D levels would slowly go down. How fast depends on how much vitamin D you have stored in your fat reserves. It would be natural to assume that your fat reserves would be saturated with vitamin D, so this actually only depends on the total amount of fat reserves you have. This then points to a very clever mechanism:
2) Vitamin D’s real role in the body is to act as a signal. Calcidiol levels lower than the maximum attainable via solar exposure is a signal that the prospects for getting enough food from Nature in the near future is below optimal. Clearly when the Sun no longer rises high in the sky in the afternoon in Fall, this is a signal that hard times are coming and the smart thing to do is to save mor energy from each meal. This is better than waiting until food shortages arise before taking any measures. And the less fat reserves you have, the earlier in Fall you want to start. So, what would you cut back your energy spending on? It seems sensible to start with things that do not pose any risk to your health. So, you can imagine that as calcidiol levels drop from 220 nmol/l to 180 nmol/l, all that happens is that the body does not invest as much in maintaining optimal fitness levels. If you run a marathon, you will not recuperate as fast as you are used you. Thing is that even if you do not run a marathon, keeping your body in shape so that you could recuperate fast, costs energy.
Then as your calcidiol levels go down further, more energy saving measures are taken. But these now have increasing risks for your health. The lower your calcidiol levels become the more serious the prospect of severe food shortages is estimated to be, hence it pays to take more risky energy saving measures. When calcidiol levels sink below 150 nmol/l, less energy will be made available to your immune system. You’ll lose some very expensive layers of defense that you can do without in almost all circumstances anyway. The risk of certain diseases may then increase, but you save a lot more energy, making it more likely that you will survive the Winter.
Then when Winter arrives and your calcidiol levels go below 80 nmol/l, you will cut back on other expensive processes in your body. E.g. getting calcium from food is not free of charge. There are enzymes that have to be produced that do this. By cutting back on this, you may get a bit less calcium from food, but you then save energy. You will still get enough calcium from food if you get 1 gram per day, but if you get 400 mg or less per day, the body will get some of it from the bones. Because the calcium in the bones is very concentrated, it costs less energy to get it from there than from the food we eat. When calcidiol lelvels get below 20 nmol/l, you will struggle to get enough calcium from food, even if it is rich in calcium. You can imagine that such low levels point to it being late in Winter and you having lost quite a lot of your fat reserves, so you want to extract as much energy as possible out of every meal that you eat.
Of course, this is just my speculative theory, but it is the only thing I can think of that makes sense. Why else would animals have evolved to make maintaining their bones artificially dependent on a chemical that is not going to be produced when the Sun is not high in the sky? Note that vitamin D itself does not get the calcium out of food, it merely switches on genes that code for the proteines that do this.
3) It is now recommended that babies get 400 IU per day from supplements. This has been shown to be necessary and siufficient. However, one can ask why Nature hasn’t taken care of this. Why is there not enough vitamin D in breat milk? It turns out that if lactating women have calcidiol levels of about 150 nmol/l or more, their breat milk actually does provide for the 400 IU per day for their babies. It is just that almost no women living in the West have such high calcidiol levels. Women need to use at least 6700 IU per day to get such high calcidiol levels. This fits in with my theory that the RDA should be 10,000 IU per day leading to calcidiol levels of around 220 nmol/l, because 150 nmol/l is a threshold value where the body is on the verge of cutting back on providing the best care for its baby.
4) 10,000 IU per day is guaranteed to be safe. Obviously a dose that you would naturally get from Nature is unlikely to be unsafe. But direct tests also point this out. It is estimated to be at least a factor 4 below the minumum value at which you can expect that some people could get hypercalcemia. A test in which 50,000 IU per day was given to people for 8 weeks showed no evidence of elevated calcium levels. The calcidiol level of some of these people was higher than 600 nmol/l. While it cannot be ruled out that in some people you could see hypercalemia at these levels, it should still be rare. The safe limit for calcidiol is set at 500 nmol/l and 220 nmol/l is so far below this value that one shouldn’t worry about it.
5) Last but not least: I’ve improved my fitness by quite a bit since starting to take vitamin D supplements