You are much more likely to get sick from a flu shot for one reason or another than from Sunshine/D-3. I would venture to guess that if you do both shots and D you will be sick more likely than if you do the D alone. The government says each year that the shots are only 20% or 60% or some % effective and never 100%. I admit my sample is small, perhaps a couple of dozen people I have successfully proselytized and a few more I know who were already doing it. Over the time that all of them have been using the supplements there has been zero flu among them. I would say zero colds but some are subject to seasonal allergies and sometimes one can’t tell for sure. Three, including myself 9 years ago, used megadoses (900 iu per pound of body weight) to end almost immediately -12 hours or less- highly debilitating cases of flu.I got a flu shot in 1966 that almost knocked me out of the Air Force and have not had one since.
It is important to tread carefully in advising against vaccines, as even the Vitamin D Council notes that in the research, there are some important provisos (stipulated conditions.)
https://www.vitamindcouncil.org/health-conditions/influenza/
“A study was done that looked at the levels of vitamin D in people with prostate cancer and their immune response to the influenza vaccine. This study found that people who had higher levels of vitamin D had a higher response to the vaccine, meaning that they would be more protected against getting influenza.”
“In experiment done with Japanese schoolchildren looked at the effects of vitamin D supplements on their chances of getting influenza... There was a preventive effect of 1,200 IU vitamin D per day on children getting influenza A... In this study, there was no effect of vitamin D on influenza B, possibly because vitamin D may respond in different ways to the inflammatory proteins in the viruses.”
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“There are two branches of your immune system: the adaptive and the innate. The adaptive immune system develops based on previous exposure to a virus. The innate immune system is the part that can respond quickly to foreign invaders, and is based on the levels of immune cells and proteins you have.”
I wanted to cite this in the article for an unrelated reason. That is factors *beyond* Vitamin D or vaccines that can strongly impact influenza.
To start with, obesity. In the white fat of the body are what are called MAST cell clusters.
https://en.wikipedia.org/wiki/Mast_cell
They have been described as bags full of histamines and other chemicals that cause an immune response, typically to allergies, but also to the flu. When irritated they not only start to release chemicals, but these chemicals irritate other MAST cell clusters. As such, they are to a great extent responsible for the “cytokine storm” overreaction to new pathogens. Vitamin D is an ACE inhibitor, that helps to moderate these MAST CELL clusters.
https://en.wikipedia.org/wiki/ACE_inhibitor
This relates to obesity in an odd way. Because when people become overweight, their increased white fat cells also gets more MAST cell clusters, in a greater than proportional way. So people who are morbidly obese have a LOT of these MAST cell clusters. They strongly impact auto-immune diseases like arthritis and psoriasis, etc.
And beyond a certain amount, vitamin D can’t moderate them any more. This is why obese people are much more susceptible to influenza than people of ordinary weight.
The other notation is about how the semi-metal arsenic can foul the immune system. It interferes with *both* the adaptive and innate parts of the immune system. First by inhibiting the adaptive part, so that it does not detect a new and dangerous pathogen until it gets a foothold in the body. And then, when it does recognize the pathogen, the innate immune system goes wild with a cytokine response, far more than Vitamin D can moderate.
So, don’t eat arsenic. (I’ll note that the USGS allows just a minuscule amount of arsenic in drinking water, and is very serious about it. So the biggest exposure of most people is from wood preservative.)