How are your sons calcium levels?
Vitamin D is essential for promoting calcium absorption in the gut and maintaining adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and prevent hypocalcemic tetany.
http://ods.od.nih.gov/factsheets/vitamind.asp
My calcium levels seem to be okay at the moment although my Vitamin D levels are low, but they are checking these on a regular basis. I am also awaiting a bone scan, but I think this is more in relation to having Coeliac disease.
My sons levels were also below 10. He rarely makes it outside to get sunlight. They have him taking 2000 ui a day. I read a healthy level starts at 50, so you should also probably be taking a supplement. They are going to recheck his levels in 2 months.
I also have low Vitamin D levels, I think mine are either 5 or 7!! Strangely I have not been put on any treatment for this although my neurologist has asked for my deficiencies to be treated.......this is something I need to speak to my GP about - just need to be well enough to be able to go and attend an appointment!!
As I am aware it is common for people with a chronic illness to have low Vit D levels. I hope he does experience some symptom relief from correcting his levels x
I am not sure about the benefits, but in order for your body to absorb Vit D, you also need Vit C. So you may want to check on that so he can get the full effects.
I also don't know what symptoms he is having, but some say magnesium and phosphorus seem to help also. Just thoughts