Dr. John Faul:

We have looked at people who had Covid and were vitamin D deficient and looked at them in clinic six months afterwards. While 75% of them were vitamin D deficient when they were sick, when we told them to take supplements and gave them prescriptions for a period of 1,000 units a day, 35% were still deficient at the end of it. It was better but not great. Obviously people forget to take the tablets. When we asked them afterwards, they were not quite clear that it was important. They said they took them for a little bit but then forgot. The levels would go up after two to three weeks but even six months later people tend to forget. That is why the messaging has to be important, strong and persistent about vitamin D supplementation.

How long does it take to improve one's immune system? Generally, we would say that if one impacts one's immune system severely - for example with a high dose of steroids - it takes about three months for one's lymphocytes to recover from that. If one has, say, a death in the family, then three to six months later one gets shingles, it means one's immune system is hit in some way. We think the same is for recovery. When one tries to boost someone's immune system - say, the person comes off chronic steroids - one's immune system only really recovers three to six months later. It is at least three months. That is why there is an urgency about getting supplementation into people now because time is moving on. The commonest thing that our patients are asking us is why were they not told this last year as it could have saved so much trouble considering it takes months to build up one's levels.