I was wondering whether one's vitamin D needs increase significantly during periods of stress, e.g. when you're ill. It's been suggested that consumption of wheat bran increases the rate at which the body burns through vitamin D (perhaps because wheat consumption provokes an immune response), but does the same apply with illness or other physiological stressors.
At present I try to keep my vitamin D intake (no sun most of the year) to 5000IU per day which, in theory, should get me into a healthy range (since it's been posited that 1000IU typically increases levels by 10ng/mL) and since I think I'm pretty healthy and pretty light and eat a fair amount of oily fish (mackerel/sardines) too. If I do get a cold however, would it necessarily be a good idea to consume extra vitamin D on the assumption that I'm using it up quicker, or would there be no rationale behind this other than 'if I'm ill, my vitamin D must not be high enough' (which seems fallacious)?
Every vitamin D molecule is a one shot pass for a cell to access cellular DNA as to how a cell needs to respond to a stimuli. A cell under attack by a virus makes use of many more molecules of vitamin D.
A cell cannot think, all its instructions are preprogrammed and stored in the DNA. The DNA is locked and vitamin D is the pass card to access DNA instructions. The pass card can be used only once and is detroyed.
When you are sick your body uses much more vitmain D accessing the DNA for instructions.
Stressors on the body, including exercise, illness, and psychological stress, sleep deprivation, etc, all increase the need for all nutrients. But how much is the need truly increased I think is the real question. If your needs go up by 20% (a number I just invented for fun) over the course of a week, but your body levels of D were already totally stocked up, then I think you would be fine. The body stores D for a good long while. I think the main goal for us is to always have plenty and that is why some people supplement, exactly so they will not dip far into their D stockpiles should germs attack or any special need comes up. I personally do not think you need more D if you are were already well stocked, taking plenty more in, and are only sick for a short while. Of course, the only way to really know your status is to test your blood. It's tricky to give advice when you don't know your true D status. I'd say get your D status to good levels and then just float with that as your guide. It's unlikely you will be able to effectively micromanage intake beyond that for every stress or head cold you get through the months. My advice would be to also check all other nutrient intakes as well. Many other nutrients can also have strong effects on health.