I will start by saying I cannot advise anyone to take Vitamin D. It is outside my scope of practice. However, I can say that during this whole period I have made sure that my family members are taking supplements including Vitamin D because there is a clear body of evidence about how important it is in relation to the immune system.
Vitamin D is called the sunshine vitamin and yet it is so much more than that. It is also a hormone and essential to the function of our immune system as well as bone health and a number of other important body functions.
Due to our position on the planet and our lack of sunshine days for much of the year this is something we are very deficient in overall in places like the UK, Canada and northernmost parts of Europe. Most functional medicine practitioners know the value of Vitamin D and indeed I have friends and family who after simple blood tests after feeling very rundown realised they were very deficient in Vitamin D. It can be prescribed on the NHS by a doctor.
Vitamin D works synergistically alongside vitamin K2 and also uses a lot of magnesium when it is used in the body. Therefore, it is a good idea to read a lot more about how it works and with what as just taking vitamin D on its own can cause some issues, for example, in higher doses it may cause calcium deposits to go in the kidneys as stones rather than on the bones.
It is also a fat soluble vitamin rather than a water soluble one. There are a number of good food sources for it yet often these foods, such as liver, are not in people's regular diets nowadays.
Disclaimer: I am not a medical professional and my blog is not given as medical advice- if you want to take a supplement then discuss it with your GP and/or a pharmacist first and foremost.
The NHS says this https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/ which is a very conservative figure.