Out of curiosity, have you taken Vitamin D supplements before for a longer period of time? If yes - what was the daily dosage ?
Have you taken flu shots at the beginning of the season?
I take 2,000 IUs of extra Vitamin D a day and we all got the flu shot in September. From what I've read, this year's flu shot is largely ineffective.
This is a brutal flu. If you catch it, stay home and get rest.
Basically during Fall as the amount of sunlight drops our bodies vitamin D, for which there is clinical evidence that it helps with immunity, drops leaving us more susceptible to infections leading to the overall flu season starting in Jan/Feb time frame. As the sunlight picks up, vitamin D increases and flu season tapers off.
Anecdotally: I have seen a couple studies pop up recently talking about how daily value of vitamin D has been wrong for a long time. This makes me think taking vitamin D might be the new fad medical thing to do, kinda like how going gluten free was the big thing a couple years ago.
For transparency I have not read all of these but they all have popped up recently: https://news.ycombinator.com/item?id=15867918 https://news.ycombinator.com/item?id=16062697 https://news.ycombinator.com/item?id=15877289 https://news.ycombinator.com/item?id=15687217
[0]https://www.health.harvard.edu/blog/vitamin-d-whats-right-le...
Alternative thoughts on adequate vitamin D: https://www.vitamindcouncil.org/i-tested-my-vitamin-d-level-...
https://www.ncbi.nlm.nih.gov/m/pubmed/28768407/
Vitamin D is relevant to proper functioning of immune system, however it seems that it is hard to find "the right amount" for everyone as it depends on several factors.
I'm wondering if Vitamin D intake can improve response against recurring infections like flu, sometimes they can bring you down several times in a season, so it takes quite a heavy toll on productivity and mood.
Edit: I am taking 5,000 units daily. Didn't have the flu vaccine this year.
In my defense the parent comment was asking for anecdotal evidence.