-- 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.
Also, look at the timings:
Received: 16-09-2025
Accepted: 29-09-2025
Available online: 14-10-2025
That's relatively fast but also the paper is not super in-depth.
And in general it seems like that the "International Journal of Medical and Pharmaceutical Research" is not quite well known.
See the Editors, not even pictures there: https://ijmpr.in/editorial-board/
> Incidence of ARIs was documented through monthly follow-up visits and self-reported symptom diaries validated by physician assessment.
This is basically impossible to accomplish for 386 participants who aren't in some form of captivity (e.g. incarcerated, institutionalized, in the military, or a boarding school). Nobody cares enough to maintain a "self-reported symptoms diary" and make monthly visits for some study. If they actually ran the study as designed, they would've have zero usable participants even starting from 400.
Saying nothing of the ethics of giving half the Vitamin D deficient patients presenting at your clinic with a placebo.
> (e.g. incarcerated, institutionalized, in the military, or a boarding school).
That's a pretty big list. Add Retirement communities and your pool increases even more. Add to that the fact that this is India where the population is at least 5x bigger and much more concentrated..
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.
While I find your comment enjoyably pithy, in the case of vitamin D, many humans are currently living at latitudes which they are not suited to (skin being too dark to generate enough vitamin D given the insolation), and eating diets which do not provide them with sufficient amounts of it (the carnivore diets of Inuits and similar groups being a good contrast).
It’s criminal that the US sent Somalian refuges to live in Minnesota. Those are some seriously brown people in the land of no vitamin D. Pretty big population in Seattle as well, which is worse due to cloud cover.
While I’d love to just go for a walk outside, the allergen exposure of the outdoors is too high most of the time. This elements any mental health benefits a walk in a forest might otherwise give.
The issue I've found with these discussions is it appears there's mixed evidence on if vitamin D *supplementation* actually has a positive impact, regardless of vitamin D deficiency. In other words, is the deficiency causal or correlative.
I have no opinion on the matter, and am inclined to think there is at least some positive benefit. But YMMV
Most of the vitamin D supplement studies have been very low quality in that they give all subjects in each group a fixed amount (or placebo). Ideally they should periodically test blood levels and titrate the dose to hit a target range. This would get us closer to establishing causality (or lack thereof) including a response curve. The amount needed to hit a given target will be wildly different for many individuals based on factors that are still not well understood.
Just my results (n=1) and I don't think this is exactly what you were saying, but just in case other read it the same way I did at first: having had (lab tested) vitamin D deficiencies, vitamin D supplementation can help to restore levels back into the desired range. So supplementation can have the desired effect of improving vitamin D levels (more below). It is a simple test that most doctors don't quibble about adding on to other blood tests (i.e. during annual checkup, for instance), but isn't generally checked by default. (note: insurers may want it to be "diagnostic" rather than "preventative" in order to cover the test.)
Whether it has a "positive impact" on overall health (which I believe to be your point), that would be even more anecdotal and also impossible for me to narrow down whether that one factor had any significant effect, so I won't posit that. And I agree that from different studies I've read, the actual science on it is pretty varied and I haven't seen anything conclusive. Even this study notes their conclusion was "... among adults with suboptimal baseline vitamin D levels".
This is solely my own anecdote, but I used to get bad seasonal depression every winter. I tried a number of interventions short of medication; none moved the needle very much. I started supplementing with vitamin D probably 8 years ago and haven't had any issues with seasonal depression since.
I'm pretty personally convinced that it was the supplements that helped here.
I took a blood test several weeks ago, my Vitamin D level was 14 ng/ml. I was so fatigued there were times I had to lay on my office floor because I didn't even have the energy to sit in my chair. I started taking 50k IU's weekly and then 10k IU's daily, and the results were dramatic. I went from having 0 energy to nearly normal. I also had soreness in my legs which went away.
Vitamin D isn’t technically a vitamin in the strict sense, because unlike the other vitamins the human body can produce it itself (by exposure to sunlight).
The body can also synthesize vitamin A from beta-carotene which is effectively two vitamin A molecules joined together (one rotated 180deg relative to the other).
For most people just eating a good balanced diet and they are good to go. There are a few with genetic/biological issues and they need more - ask your doctor. Vitamin D is one that modern lifestyles likely don't get enough of and so probably worth it - again talk to your doctor.
Uncalled for. GP is pointing out that the fact the human body can produce Vitamin D means it is not a vitamin.
vi·ta·min
/ˈvīdəmən/
noun
any of a group of organic compounds which are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized by the body.
Glad to see this study, seems decent, but for a different perspective there was a relatively recent meta-analysis on the effectiveness of Vitamin D for RIs that suggested no effect:
One significant difference in this study is that it focused on people with low baseline vitamin D (10-30 ng/mL 25(OH)D), and moderate intervention (2000 IU daily).
The meta-analysis you posted did perform subgroup analysis on people with low baseline vitamin D (<25 ng/mL), but this included a wide range of intervention levels, 90% of which were <2000 IU daily equivalent. They also performed subgroup analysis on high intervention levels, but this included a wide range of baseline vitamin D, 90% of which were >25 ng/mL.
And also there's a difference between infection incidence, intensity, and duration, the evidence I've seen has been strongest in reducing intensity and duration. Also dosage might just be too low.
I've been feeling a little off lately with some respiratory symptoms and took 25,000 IU of Vitamin D, in people who are deficient (probably me lately) 400-1000 daily dose might not actually do enough to have an effect.
It's about time for a meta-meta analysis comparing the traits of the different sets of papers (N, dosage, deficiency status, time of year, duration/incidence/intensity, etc)
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.
"Winnipeg, Manitoba" ... "only need 15 minutes of sunshine per day to get your recommended dose of Vitamin D"
That doesn't apply to you most of the time, unfortunately. Vitamin D is the result of UVB exposure. For significant portions of the year, you don't get very much [1], compare with, say, [2] Orlando Florida in the US. 10-15 minutes is for a UV index of 7 [3], so that's only 4-6 months out of the year for you. And just based on my couple minutes with Google here, that number may also include the assumption that you're not just "out in the sun" for 15 minutes, but basically sunbathing. Lesser exposure may take longer: [4] Winter times can be effectively impossible because you can't sunbathe at 10 below (regardless of which scale I'm talking about) and you're not going to spend the requisite hours in the sun for what little skin is exposed. Or they can be outright impossible if your skin is dark enough.
I take 5000 IU per day year round and have not had any issues. Research suggests you can dose 10x that without major problems, although personally I wouldn't go higher than I am already.
To help prevent vitamin D toxicity, don't take more than 4,000 international units (IU) a day of vitamin D unless your healthcare professional tells you to. Most adults need only 600 IU of vitamin D a dayhttps://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...
Vitamin D toxicity is a legitimate concern, so those dosing should be mindful of it, depending on dosage and existing serum levels. Don't action on medical advice from strangers on the internet alone, talk to you doctor or other credentialed medical practitioner you work with if needed.
You probably have to really try to take too much Vitamin D with any over the counter supplement (<=5,000 IU), especially if you live that far north. For reference, a prescription dose for someone who is low is usually 50,000 daily.
It should be part of your standard blood tests so you should know if you're running high or low and your doctor can recommend or prescribe a good dose.
With 5,000 IU sometimes taking several at a time I had blood levels of Vitamin D at the top of the range which wasn't dangerous it was just informative, "hey you're having enough, tone it down".
First know that the body will stop making vitamin D before you reach overdose quantities. This means you should take vitamin D in the morning.m rather than the evening. Second know that vitamin D is fat soluble. So if you are losing weight, you can more easily overdose if you have high levels stored in your fat. Also know the body won’t absorb as much vitamin D if you don’t take it with fat.
This can make dosing tricky. You can be taking an amount that is safe right now, but then is too much later.
You can max out your body’s vitamin D production even on a cloudy day, though the sun’s angle of incidence effects production.
The body typically maxes production at something like 20k iu (pleae verify this number it has been a while since I learned it), so staying below this number should mostly safe.
The USDA has set its recommended daily allowance mostly to avoid rickets. It is largely considered too low a number for general well being.
I live in north western Washington, and previously used to combat seasonal affective disorder, with some pretty dark thoughts come february. Since I started taking 1k D3 some 20 years ago much of the seasonal mental health has gone away. I take 2k D3 consistently currently, and if I run out for more than a week my mood starts to deteriorate quickly. I still haven’t proved causation since there are likely reasons I’ve let myself run out of the supplement that long, but it is so consistent that I treat it as causal at this point. YMMV
Please do research above just asking a forum for dosing advice though. This is a well educated place, and I would very much trust it as a starting point, but there is a lot of good published content on the topic. Though, I admit google is so bad today, I might fail to find any of the content I referenced years ago… if you use chatgpt make sure to require references, and check them. I find that using multiple instances to review research references separately prevents some context based poisoning as well. And pointing out inconsistencies can be a good way to find nuance in a topic. Though sometimes LLM will just waffle, and the context may be done
I've heard the 15 minutes is all you need. I've also heard that in winter the sun is so weak that no amount of sunshine gives you any. (even if you were naked outside in winter - risking frostbite).
I'm not a medical doctor. I cannot evaluate any of the above claims. I wish I could find a source I could trust.
Depends on where you are. Latitudes above roughly 35 degrees N, the sun is too low in the sky roughly between October and March to allow for UV-B rays to penetrate, which is what your skin needs to synthesize vitamin D.
So yes, if you live in the northern regions, you don't produce any at all from sun exposure, even on a bright sunny day, during most of the year.
Up here in the PNW, even in the summer, you only have a window of roughly 4 to 5 hours where the sun is high enough, in July.
I've heard things like you only need 15 minutes of sunshine per day to get your recommended dose of Vitamin D
The figure I read years ago was that it takes 15 minutes in short sleeves to get the necessary light exposure at the 45th parallel in winter. I'm right at the 45th parallel and I don't go out in short sleeves in the winter, so I imagine it's significantly worse for you!
You don't need to guess, go to your GP and get yourself tested. It's not expensive, depending on where you're from it might even be free, and usually you get the results back already the next day.
Generally agree, but unlike water-soluable vitamins, vitamin D can store excess in fatty tissue and the liver, and so if a person takes a large dose (generally 10,000 IU daily or more), they could develop toxicity over time due to the build-up. That's why it's important to test and adjust dosages according to the data.
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."
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).
Readit News
-- 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.
"Assistant Professor, Department of General Medicine, Arundathi Institute of Medical Sciences, Dundigal, Medchal Malkajgiri, Telangana, India"
The 2nd author is listed here: https://aims.ac.in/general-medicine/ I did not find any trace for the other two authors (do they exist?).
Also, look at the timings: Received: 16-09-2025 Accepted: 29-09-2025 Available online: 14-10-2025
That's relatively fast but also the paper is not super in-depth.
And in general it seems like that the "International Journal of Medical and Pharmaceutical Research" is not quite well known. See the Editors, not even pictures there: https://ijmpr.in/editorial-board/
https://aims.ac.in/general-medicine/
> Incidence of ARIs was documented through monthly follow-up visits and self-reported symptom diaries validated by physician assessment.
This is basically impossible to accomplish for 386 participants who aren't in some form of captivity (e.g. incarcerated, institutionalized, in the military, or a boarding school). Nobody cares enough to maintain a "self-reported symptoms diary" and make monthly visits for some study. If they actually ran the study as designed, they would've have zero usable participants even starting from 400.
Saying nothing of the ethics of giving half the Vitamin D deficient patients presenting at your clinic with a placebo.
That's a pretty big list. Add Retirement communities and your pool increases even more. Add to that the fact that this is India where the population is at least 5x bigger and much more concentrated..
Dead Comment
Dead Comment
Man keeps trying to bring the outdoors inside.
The UK also consumed a lot more liver than it does today I imagine...
Man want both good of indoors and good of out outdoors.
The practical man uses technology to offset the prison built for him. The hapless enabler farms “pithy” HN points in his LED-lit room.
Deleted Comment
1 https://www.mdpi.com/2072-6643/17/17/2744#:~:text=highest%20...
2 https://www.abs.gov.au/articles/vitamin-d#edit-group-image--...
I have no opinion on the matter, and am inclined to think there is at least some positive benefit. But YMMV
If a 100 people take 50IU of Vitamin D, you get 100 different results.
Some get enough from minor sun exposure and maybe eating a fish now and then. Others need massive doses to get any results.
Whether it has a "positive impact" on overall health (which I believe to be your point), that would be even more anecdotal and also impossible for me to narrow down whether that one factor had any significant effect, so I won't posit that. And I agree that from different studies I've read, the actual science on it is pretty varied and I haven't seen anything conclusive. Even this study notes their conclusion was "... among adults with suboptimal baseline vitamin D levels".
I'm pretty personally convinced that it was the supplements that helped here.
I took a blood test several weeks ago, my Vitamin D level was 14 ng/ml. I was so fatigued there were times I had to lay on my office floor because I didn't even have the energy to sit in my chair. I started taking 50k IU's weekly and then 10k IU's daily, and the results were dramatic. I went from having 0 energy to nearly normal. I also had soreness in my legs which went away.
Deleted Comment
Dead Comment
vi·ta·min /ˈvīdəmən/ noun any of a group of organic compounds which are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized by the body.
> The study protocol was approved by the Institutional Ethics Committee and registered with the Clinical Trials Registry of India
As far as I can tell, that registry is here: https://www.ctri.nic.in/Clinicaltrials/pubview.php
Doing a keyword search for the first author's last name reveals zero hits. (It's possible I'm missing—that search does not inspire confidence.)
https://www.thelancet.com/journals/landia/article/PIIS2213-8...
The meta-analysis you posted did perform subgroup analysis on people with low baseline vitamin D (<25 ng/mL), but this included a wide range of intervention levels, 90% of which were <2000 IU daily equivalent. They also performed subgroup analysis on high intervention levels, but this included a wide range of baseline vitamin D, 90% of which were >25 ng/mL.
I've been feeling a little off lately with some respiratory symptoms and took 25,000 IU of Vitamin D, in people who are deficient (probably me lately) 400-1000 daily dose might not actually do enough to have an effect.
It's about time for a meta-meta analysis comparing the traits of the different sets of papers (N, dosage, deficiency status, time of year, duration/incidence/intensity, etc)
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.
That doesn't apply to you most of the time, unfortunately. Vitamin D is the result of UVB exposure. For significant portions of the year, you don't get very much [1], compare with, say, [2] Orlando Florida in the US. 10-15 minutes is for a UV index of 7 [3], so that's only 4-6 months out of the year for you. And just based on my couple minutes with Google here, that number may also include the assumption that you're not just "out in the sun" for 15 minutes, but basically sunbathing. Lesser exposure may take longer: [4] Winter times can be effectively impossible because you can't sunbathe at 10 below (regardless of which scale I'm talking about) and you're not going to spend the requisite hours in the sun for what little skin is exposed. Or they can be outright impossible if your skin is dark enough.
[1]: https://winnipeg.weatherstats.ca/charts/forecast_uv-monthly....
[2]: https://nomadseason.com/uv-index/united-states/florida/orlan...
[3]: https://overcomingms.org/program/sunlight-vitamin-d/uv-index...
[4]: https://vitamindwiki.com/dl2105?display
edit: seriously though, anything warmer than -10C you'll definitely see kids in shorts. I go skiing in shorts every year.
https://pubmed.ncbi.nlm.nih.gov/30611908/
To help prevent vitamin D toxicity, don't take more than 4,000 international units (IU) a day of vitamin D unless your healthcare professional tells you to. Most adults need only 600 IU of vitamin D a dayhttps://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h...
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
It should be part of your standard blood tests so you should know if you're running high or low and your doctor can recommend or prescribe a good dose.
This can make dosing tricky. You can be taking an amount that is safe right now, but then is too much later.
You can max out your body’s vitamin D production even on a cloudy day, though the sun’s angle of incidence effects production.
The body typically maxes production at something like 20k iu (pleae verify this number it has been a while since I learned it), so staying below this number should mostly safe.
The USDA has set its recommended daily allowance mostly to avoid rickets. It is largely considered too low a number for general well being.
I live in north western Washington, and previously used to combat seasonal affective disorder, with some pretty dark thoughts come february. Since I started taking 1k D3 some 20 years ago much of the seasonal mental health has gone away. I take 2k D3 consistently currently, and if I run out for more than a week my mood starts to deteriorate quickly. I still haven’t proved causation since there are likely reasons I’ve let myself run out of the supplement that long, but it is so consistent that I treat it as causal at this point. YMMV
Please do research above just asking a forum for dosing advice though. This is a well educated place, and I would very much trust it as a starting point, but there is a lot of good published content on the topic. Though, I admit google is so bad today, I might fail to find any of the content I referenced years ago… if you use chatgpt make sure to require references, and check them. I find that using multiple instances to review research references separately prevents some context based poisoning as well. And pointing out inconsistencies can be a good way to find nuance in a topic. Though sometimes LLM will just waffle, and the context may be done
I'm not a medical doctor. I cannot evaluate any of the above claims. I wish I could find a source I could trust.
So yes, if you live in the northern regions, you don't produce any at all from sun exposure, even on a bright sunny day, during most of the year.
Up here in the PNW, even in the summer, you only have a window of roughly 4 to 5 hours where the sun is high enough, in July.
The figure I read years ago was that it takes 15 minutes in short sleeves to get the necessary light exposure at the 45th parallel in winter. I'm right at the 45th parallel and I don't go out in short sleeves in the winter, so I imagine it's significantly worse for you!
Unless you eat the pills like candy, you're safe.
[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
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).