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Newsflash: When you are sick, addressing comorbid conditions helps you get better faster.
Anecdotal but when I'm sick I double my vit C and D intake which typically helps me.
I live in Winnipeg, Manitoba where it is quite cold for a big majority of the year. I have dabbled with supplements because I get a couple of major colds every year.

I've heard things like you only need 15 minutes of sunshine per day to get your recommended dose of Vitamin D, but I've also heard it can be quite bad for you if you have too much in your system (and it's hard for your body to flush excess amounts).

If there a safe level of Vitamin D supplements where you won't run this risk? I don't drink milk either because I'm lactose intolerant.

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Can confirm anecdotally. I used to get 2-3 colds a year for about 15 years straight, especially during season changes when the humidity levels changed. Started taking 5000 IU vitamin D3 daily about 2 years ago and I haven't gotten sick since.
Vitamin D, red light therapy, insulin attenuating response of a walk, immunological benefit of allergen exposure, cognitive noise reduction and rest response of walks in forests.

Man keeps trying to bring the outdoors inside.

I wonder why we didn’t recommend vitamin D during Covid?
Unfortunately Vitamin D deficiency tests (probably it is not covered by your insurance), high dose supplements are currently pushed so much by Doctors I started to think this is almost a scam. Most of the research about the subject are very noisy and conflicting.
"Exercise" not found in the shared text.

I'm sure people who supplement or have good D levels also take care of themselves, generally - because they know D is one of the supplements that make a difference both somatic and psychological.

And thus do better with flu/cold.

Just turn on an uv light for a few hours. Problem solved.
Supplementing with vitamin D is honestly one of the easiest things you can do... it's cheap, available everywhere, and makes a real difference. Just make sure you're also taking magnesium citrate (or another good form of magnesium) with it, since your body needs magnesium to properly use vit D
3-4 years ago this submission would be flagged in seconds just because of the word Vitamin D.
I take 10k IU of vitamin D if I feel a cold coming on. I used to get extremely bad colds very frequently, and every time I get frustrated and read whatever research might be helpful. A year ago I came across some info about LL-37, and found that vitamin D might help, and that's when I started taking it. https://pmc.ncbi.nlm.nih.gov/articles/PMC9134243/

The big dose of D seems to help. I'm certain I'm deficient, since I already take 2-4k daily, which noticeably helpsy winter blues. It's the first time I can "arrest" a cold, and even if I get sick the symptoms aren't nearly as bad.

My full protocol for if I start feeling a cold is this:

1. 10k vitamin D 2. Stay extremely warm when I sleep. Uncomfortably warm. 3. Butyrate (probably a placebo) 4. Curcumin (almost certainly a placebo).

I personally found that taking vitamin D regularly dramatically reduced how many colds I got (10 in 2024 vs. 1 in 2025).

I take 2,000 IU per day, typically without a meal.

In the US it is very easy to test your vitamin D levels. I recently had mine done and was just below normal range. Started supplementing and will test again in 6 months.
I wonder if adding zinc on top of this would do.
Interesting how your government did not mention Vitamin D during the COVID scare.
A few other interesting links with Vitamin D absorption. Surprised nobody has brought up gut dysbiosis and the role microbiome plays in Vitamin absorption. I'm finding it increasingly difficult to discern whether the things we consume are for the direct benefit of our cells and metabolic needs or via a more indirect path if the things we consume directly affect the microbiome within us which then translates into either nourishment or inflammation within us. Since microbiomes can change rapidly in composition, this feels like a game of nurturing over the long-haul with some minor blips along the way.

[1] "connection between vitamin D and the immune system through gut bacteria and may have applications for improving cancer therapies"

[2] "How the Gut Microbiome Affects Vitamin D Absorption"

[3] "vitamin D may affect the host-microbiota relationship."

[1]: https://www.science.org/doi/10.1126/science.adh7954

[2]: https://www.gutnow.com/medical-treatments/how-your-gut-micro...

[3]: https://journals.asm.org/doi/10.1128/spectrum.00083-24

Heh...this is a shady study if I ever saw one.

-- Exactly 400 study participants recruited.

-- Exactly 193 of 200 participants completing the study in each group (which, for a study administered in a community setting, is an essentially impossibly-high completion rate).

-- No author disclosures -- in fact, no information about the authors whatsoever, other than their names.

-- No information on exposures, lifestyles, or other factors which invariably influence infection rates.

-- Inappropriate statistical methods, which focus very heavily on p values.

-- Only 3 authors, which for a randomized controlled trial involving hundreds of people in different settings with regular follow-up, seems rather unlikely.

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I was pretty sure we already knew vitamin D deficits dampen the immune system.