Vitamin D: the New Covid-19 Chloroquine?
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However, there a a few things that are clear:
1. Calcium absorption from the intestine increases with vitamin D supplementation dose up to around 8-10,000 IU D3 daily.
2. 15 minutes of full body exposure in noon sun is equivalent to a dose of ~20,000 IU D3
3. There are few cases of vitamin D overdose in the literature - doses in the 1,000,000 IU+ range within days is generally where symptoms are noted - this excludes people with kidney disorders.
Personally, I take 10k IU D3 a day. The D3 is important because D2 has 1/2 to 1/3 the effect per dose in raising calcium absorption levels.
I would recommend this level of supplementation to anyone who doesn’t have a kidney disorder.
Vitamin D is involved with calcium in the body in many different ways, specifically I was talking about a measure of the absorption of calcium into the body from food as promoted by vitamin D.
Organ calcification is extremely serious and a very understandable reason why doctors have been hesitant to recommend higher doses of vitamin D, however most medical thinking about vitamin D until recently has focused on the prevention of Rickets, which requires only a small amount of constant supplementation (500 IU D3) to avoid serious effects. In context, 10,000 IU seems like an enormous dose. However if you look at the blood serum levels of people who receive consistent UV exposure, they have much higher levels than someone who is being supplemented with 500 IU D3 and no UV. So much of this debate is around trying to find out what the "optimal" vitamin D level is rather than what level is "sufficient" to prevent Rickets.
Here's a tool that can help calculate useful exposure depending on your location/time of year. Doesn't take clothing into account however..
My pale skin in the midday desert sun for fifteen minutes in July? I'd have a pretty serious burn.
I list these numbers to give a general idea of the levels of Vitamin D that people experience without oral supplementation.
My conclusion was that too many studies were being done to determine the correct or safe amount to supplement rather than testing regularly to determine a safe/optimal blood concentration.
Very excited for good prospective studies of Vitamin D.
Because usually phisiological processes are in some kind of equilibrium and regulated, so it's not straightforward to compare it to supplements.
A bag of carrots wont hurt you yet an equivalent dose of betacarotene (vit A) supplement definitely will and is strongly associated with increasing certain cancers. There's a reason you won't see those on the shelf apart from miniscule amounts in multivitamins.
Nothing in nutrition exists in a vacuum.
I’m worried about overdosing if I take 5000 UI and get a lot of sun.
In other words, 5000IU is much lower than what the body would naturally produce when exposed to sunlight for long durations in a day (assuming good latitude, sunny season, lower atmospheric pollution, around noon, lighter skin tone, etc.).
Shots of 250,000 IU are given clinically and the therapeutic dose was traditionally 50,000 IU D2 weekly - corresponding to a dose of about 3,500 IU D3 daily.
I highly recommend getting tested for kidney disease if you are worried and get multiple vitamin D tests - the tests are imprecise but will give you a general idea of what your levels are.
However, this is I think what you are trying to get at:
One particular epidemiological study stands out as a guide for what typical 25-(OH)D levels might have been be for our earliest ancestors.
Luxwolda et al. studied populations of pastoral Masai and hunter-gatherer Hadzabe, sampling their blood for 25-(OH)D levels and taking note of their daily habits in reference to UV exposure.
The mean 25-(OH)D concentration in these populations was 115 nmol/L, with a range of 58 nmol/L to 171 nmol/L.
This study provides a general framework for the expected 25-(OH)D level of active, healthy humans working outdoors at a low (< 5 degrees) latitude. Humans have modified their living conditions greatly from this model of ancestral life, leading to reduced exposure to UV radiation.
Can increased calcium absorption lead to kidney disorders?
This is my biggest worry when taking Vitamin D3 supplements, I have Vitamin D deficiency but when I take supplements it quickly reaches to toxicity levels (> 80 ng/mL) and so I have the revert to monthly supplement of 60,000 IU of Cholecalciferol.
PSA: I'm a dwarf, possibly Achondroplasia, but during childhood (4 - 15years) I wasn't categorised as such and my bone troubles were always attributed to Vitamin D deficiency. After age 17, I didn't have much of bone problems and so I didn't follow up on my Vitamin D deficiency.
Fast forward to age 32, I was diagnosed with Spinal Stenosis among other cerebral spinal fractures risking becoming quadriplegic[1]. So, if you have bone problems due to Vitamin D deficiency, please follow it up regularly, it's likely going to be life-long but taking proper supplements is better than a fracture. Also visiting a good endocrinologist to get to the root of Vitamin D problems is recommended.
[1]https://abishekmuthian.com/i-was-told-i-would-become-quadrip...
I hope you are receiving the treatment you need.
It is certainly true that a few high dosages of vitamin D are not harmful. The issue is the negative effects of having too high of a vitamin D status.
Anyone taking more than 2k IU/day should do so after consulting their doctor or at least testing of their vitamin D levels.
Be careful of anyone claiming to be an expert on anything, especially on an anonymous forum - even if that forum has in general higher quality opinion.
And the OP does not mention Vitamin K2 at all. How does anybody who claims to have done a Masters on Vitamin D not mention K2?
Personally, I eat dark green leafy vegetables every day - one serving of kale contains 443% daily value of vitamin K and I probably consume 2-3 servings a day.
Most food we eat doesn't contain vitamin D. A serving of farmed salmon, for example, contains about 250 IU D3 - 32% of the daily value.
In any case, I highly agree with not trusting anonymous internet opinions.
I've been taking vitamin d3 10K IU/day for 10 years and it has allowed my blood V-D3 levels to go from 12 ng/mL to ~50 which is within normal range. The NIH recommended dose has been going up over the last 2 decades starting at 400 IU and now 4,000 IU as we learn more and more about it's effectiveness.
If you are rounding down your vitamin D status then it is currently at what the NIH say should be avoided. Have you consulted with a medical professional about your vitamin d status?
10k IU/day can be great when someone's level is 12, but it's not a maintenance dosage once at healthy levels.
"A statistical error in the estimation of the recommended dietary allowance (RDA) for vitamin D was recently discovered; in a correct analysis of the data used by the Institute of Medicine, it was found that 8895 IU/d was needed for 97.5% of individuals to achieve values ≥50 nmol/L. Another study confirmed that 6201 IU/d was needed to achieve 75 nmol/L and 9122 IU/d was needed to reach 100 nmol/L. The largest meta-analysis ever conducted of studies published between 1966 and 2013 showed that 25-hydroxyvitamin D levels <75 nmol/L may be too low for safety and associated with higher all-cause mortality, demolishing the previously presumed U-shape curve of mortality associated with vitamin D levels. Since all-disease mortality is reduced to 1.0 with serum vitamin D levels ≥100 nmol/L, we call public health authorities to consider designating as the RDA at least three-fourths of the levels proposed by the Endocrine Society Expert Committee as safe upper tolerable daily intake doses. This could lead to a recommendation of 1000 IU for children <1 year on enriched formula and 1500 IU for breastfed children older than 6 months, 3000 IU for children >1 year of age, and around 8000 IU for young adults and thereafter. Actions are urgently needed to protect the global population from vitamin D deficiency."
I have no doubt that the mainstream NIH advice is not optimal. The best thing for everyone to do though is not to recommend high dosages for everyone but instead to recommend getting vitamin D levels tested.
Vitamin D level blood testing is imprecise - I would not consider any one test of Vitamin D levels to be accurate.
This person's cited paper corresponds with the calcium absorption data that suggests around 8,000 IU D3 is where calcium absorption begins to plateau and more vitamin D leads to minimal additional calcium absorption.
Since I haven't been going outside, I take vitamin D 10,000 IU daily. You are correct in that one shouldn't just take the advice of random internet strangers - I should be more careful in posting. My personal experience with Vitamin D has been extremely positive and so I get excited about sharing what I know - of course I had to work and couldn't actively respond to this thread as much as I would like.
Things that work well for one person can be dangerous for others. It's fine to share your positive experiences, but it's another step to be recommending the same to others.
There are a lot of other factors besides calcium absorption to consider. In fact maximizing calcium absorption with vitamin D likely has negative consequences unless there is proper vitamin K intake as well.
Which is just what you did before.
For someone who claims to have done a masters on Vitamin D, I find this generalized statement disturbing. What skin tone the person has, what season it is, what latitude the person lives at, age of the person etc., are factors in how much Vitamin D is produced by the body on exposure to sunlight. I’m afraid I can’t take the other points seriously because of the brevity and lack of nuance.
My point here was meant to be about how this is essentially the daily maximum dose from UV radiation due to the isomerization of previtamin D into inactive isomers, and to give context to a dose of 10,000 IU D3 seeming large when it is half the amount a person might receive from sun exposure.
Define "full-body exposure", please? I'm not going to walk around naked outside in the sun.
Re lux with full body exposure. I was under the impression it's an hour per day to get 15-20 IU? Either way it means exposing legs, hands and face to the sun which most people rarely do on a daily basis.
Seems like such a low effort, high reward thing to do.
Depending on the latitude and skin complexion that may be all thats needed for D3.
During “flu” season I was usually sick for the entire season with a rotating assortment of viral respiratory issues, this lasted until about 7 years ago.
8 years ago in September I started taking 10,000 IU of vitamin D3 and 180mg of K2 daily.
I haven’t had a deputies illness since. My children were getting sick at their normal clip, my wife the same, but not me. I went from being sick all the time to not getting sick ever. I made one change in my life, adding the D3 and K2.
After 2 years of not getting sick my wife and children started supplementing with D3 and K2, everyone stopped getting sick. My son went off to college and stopped taking the D3 and K2 and during the winter semester he got sick twice, he had me sent him the D3 and K2, he hasn’t been sick since.
It’s a small sample size, but even at 10,000 IU daily D3 is not dangerous or expensive, the only caveat seems to be that you need to supplement with K2 or you can cause gardening if the arteries due to calcification.
My doctor thinks it’s a lot of nonsense, but then again he wants every patient on blood pressure and cholesterol medication “just in case”.
(I have celiac [1], and I had to learn about this connection the hard way. The horrid thing is that my normal daily lunch was an enormous bowl of leafy greens, exactly where you're supposed to get vitamin K from, and I still had to supplement it. Calcium in the wrong places was one of the contributing factors to my heart issues in the link. I still have to be a bit careful not to eat too much hard cheese, but only slightly more careful than a normal person who faces potentially blocking themselves up anyhow.)
I supplement K2 and Mg also (plus a few unrelated things). I also get sick less, though I made enough other changes I can't tell whether to credit the supplements. (The K2 definitely helped a skin issue -- I could reliably bring it back by stopping taking the K2. That's probably a pretty idiosyncratic problem of mine, but it's an example of a supplement clearly helping.)
Chris Masterjohn has suggested that high levels of vitamin D could make you more susceptible to the virus, because some papers suggest that D upregulates ACE2 expression. He thinks it's best to aim for a blood level in the 30-35 range. I don't know how seriously to take this suggestion. For now I reduced my supplement to 1000IU/day.
Also, what dosage of D3 and K2 are you using for your kids?
Sorry the nitpicking, but may I assume you mean 180ug? That would be the normal order of magnitude for K2 supplementation.
How about this: to be in the best possible position to beat any serious infection, you need to be in generally good health.
That means having adequate levels of all essential nutrients - i.e., all the vitamins, minerals, amino acids, enzymes etc that you get from maintaining a good diet and healthy lifestyle over the long term.
To focus on just one nutrient as a pandemic looms just isn't the answer; it's not how health works.
That said, I've personally researched what nutrients (note the plural) are most important for beating an infection like this, and have adjusted my nutrient intake somewhat, and recommended to close relatives they do the same. But this is after I and they have spent many years researching and maintaining good health practices.
Update: if I was in not-so-good health (and not in medical treatment for a diagnosed condition, in which case, consult your doctor), my approach would be:
- boost my amino acids, fatty acids and minerals with a few spoonfuls of hemp seeds every day
- take extra supplements of vitamins A, B complex, C and D (and perhaps K?)
- do plenty of walking in the fresh air and sun,
- keep a generally healthy diet of good quality protein and veg.
Update 2: Others are mentioning Vitamin K, which seems like a good idea to supplement if you're generally nutrient deficient, but may not be necessary if you have a good diet. [1]
Disclaimer: not a health professional, but have had personal reasons to get very knowledgable about health and diet over many years.
[1] https://www.healthline.com/nutrition/foods-high-in-vitamin-k
Health is complex. No one is advocating ignoring all the other aspects of immune system function by paying attention to vitamin D.
[Update] I see you have toned down your comment since I started composing this response. We are in agreement.
Everybody in nutrition disagrees about specific, outsized effects. But pretty much everyone agrees what constitutes "basically healthy".
When you get your vitamins/minerals from a pill, you run the risk of your body not absorbing it because that's not how our bodies adapted to absorb those things for millions of years.
If you're eating a healthy diet (90%+ plant based whole foods), you will get more than enough minerals/vitamins and amino acids.
Taking a few spoon fulls of hemp seeds is an excellent idea: it's super high in magnesium which is a mineral that most of us are greatly lacking. But, I would consider hemp seeds as just another food part of a plant based whole foods diet. personally, i add it to salads, smoothies, etc.
And you don't need Vitamin K supplements. Greens are extraordinarily high in Vitamin K. Even, just 20 calories of Spinach will provide over 400% of your daily Vitamin K intake!
People, be especially careful with supplements, they're very much unregulated and can put almost anything they want in those things.
Nature makes the best supplements: it's called food (plant based whole foods with a variety of grains and beans, lots of vegetables and fruits and some meat) and it has everything our body needs. Yes, for vitamin D, you'll need to go outside and get some exposure to the sun. Actually, doctor's tell us, Vitamin D isn't even a Vitamin, it's actually a hormone that your body makes all on it's own with enough exposure to sun. But, based on your skin pigmentation, you may need more or less exposure.
I agree with you that most people don't eat enough fruits and vegetables. Though if someone is worried about a particular nutrient, it isn't that simple. It doesn't matter how much Vitamin K is in spinach if you don't absorb it:
>...Circulating phylloquinone levels after spinach with and without butter were substantially lower (7.5- and 24.3-fold respectively) than those after taking the pharmaceutical concentrate. Moreover, the absorption of phylloquinone from the vegetables was 1.5 times slower than from Konakion.
I don't think they have B12, you need to get that from animal sources or a pill.
People used to get B12 from the bacteria in the soil and the plants we eat. Not, anymore.
So, yes, you could eat some meat. B12 is present in very high concentrations in a lot of sea food.
When I Google "mushroom B12" it seems to suggest mushrooms have almost none.
People used to get B12 by eating meat (which I use generally to also include seafood).
This is an interesting idea. It's believed our bodies get fat to ensure we have energy when food is scarce. It makes sense that we'd also want to have vitamins available too.
This sounds like a much more specific and more testable version of that theory.
This is mostly selection bias. Society is so fat that being normal / underweight is correlated with sickness/disease.
The Ponderal Index [2] (AKA the "Corpulence Index") gives values that work for any height, with units in kg/m^3. If you are a young child or over 6 feet tall, you might find the PI/CI works better for you.
[1] https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/en...
Important to note it refers to overweight (might be referred to as "a little chubby"), not obese.
There is a lot of misinformation on the web around Vitamin D, such as that even high amounts (>= 5000IU) are tolerable and safe. After a blood test showed me Vitamin D deficient, taking 5000IU (that size is readily available over the counter at my grocery store) daily gave me disturbing heart palpitations, which I didn't realize were related to Vitamin D until after thousands of dollars in tests showed my heart to be perfectly healthy. It wasn't until I had slacked off in taking the vitamins and then started taking them again that I discovered the connection. Apparently magnesium has something to do with it, but IANAD. (I was not taking magnesium supplements at the time.) I can tolerate 1000IU occasionally, but people need to be aware that not everyone tolerates supplements (especially high doses) the same.
I was happy to see the article you linked to above only claims Vitamin D is considered safe up to 4000IU. Although IMHO, after my experience, anything over 1000IU should require a prescription. Of course nothing would stop people from taking five 1000IU OTC doses to get 5000IU, but I think most people know better than to take five of the same type of vitamin daily without talking to their doctor first.
I do not doubt your experience, but it seems incredible to me that just a 5000 IU supplement gave you heart palpitations. Then again, I've also read many reports about incorrectly labeled products (e.g. milk, supplements, etc.) which contained far more D2 or D3 than what was written on the tin, causing toxicity.
It is completely possible for "more of a good thing" to have a negative impact on you because it pushes something out of balance beyond what homeostatis can maintain. In principle the best solution is to go get more of what you need to balance it, but that can be easier said than done. Between the things that science still just plain doesn't know and the chaff of all kinds of garbage information about nutrition on the internet it can be very hard to figure out what you need.
I take roughly 5k per day in the winter and it has helped a lot. See my other post for details.
Did the supplement you took include those, or at least Mg?
Vitamin D is fat soluble, not water soluble.
The article briefly mentions this, noting that it’s possible vitamin D is just a sign of a healthy person, so of course they’ll do better with COVID. Another correlation that doesn’t get discussed whenever vitamin D comes up is that people with darker skin generally have less vitamin D, because our skin doesn’t absorb sunlight as much. We also know that COVID is disproportionately hitting colored neighborhoods in the US. Is that just because of vitamin D differences? Who knows!
By the way, if you are a person of color, you probably need vitamin D supplements. The recommended doses are for white people, so adjust accordingly.
I really loved that the whole piece was informational, and not trying to convince the reader that Vitamin D is or isn't a cure or remedy for anything. It simply presented the available facts, the research, and the positives and negatives of that research. It even explained multiple aspects and positions of the debate on whether vitamin D supplementation is good or bad.
Ideally all packaged into one tablet or something. I take an unholy cocktail of supplements to help curb my migraines, that's 5 tablets/caps a day. Not much fun.
These let you create the vitamin/supplement mix you want: https://getvitaminlab.com/
last time I tried, it ended up quite more expensive than my D vitamins.
The article "Limits of Vitamin D supplements" is a summary of the Lancet meta-analysis: "Vitamin D status and ill health: a systematic review", which is paywalled [2]. The review shows that Vitamin D supplementation has no clinically beneficial outcome on heart disease, stroke, or cancer.
FWIW, I have been supplementing with Vitamin D for over a decade. I would rather like Vitamin D to work because I have chronically low levels and it would be good to have such a good silver bullet of a nutrient. I have not stopped my supplementation but I do take more frequent walks in the Sun.
[1] https://www.outsideonline.com/2380751/sunscreen-sun-exposure...
[2] (https://well.blogs.nytimes.com/2013/12/11/limits-of-vitamin-...)
Started with 1,000 IU a day and getting sick stopped abruptly. For the last decade or so, haven't been sick more than one day, two at max, with one exception.
Yes, believe I had CV in March and "walked it off" in about 6 days or so with mild symptoms.
Last few years I've taken 5,000 IU several times a week (from Trader Joes, which has an excellent price of $4.99). As compared to Albertsons which disgustingly tries to get $15-20 for the same thing. Unfortunately this news has made both C and D unavailable at Trader Joe's for months. We'll run out soon and need to buy the gouging price somewhere else.
It's really hard for average person to accept reality: This virus, like all others, will last for a long time. We won't have, in a foreseeable future, a treatment neither a cure. Cancer, HIV or even seasonal flue are good examples examples of diseases that were discovered decades ago for which science still don't have a cure, there are a few treatments or easing medication, but none of them can be actually cured.
I expect that people will move from crazy solution to another on a regular basis until a final cure is found.. my expectation is this will last for years.
Even pessimistically assuming 90% fail, you end up with 10 vaccines.
https://www.centerwatch.com/articles/12702-new-mit-study-put...
"Approval rates ranged from a high of 33.4 percent in vaccines for infectious diseases to 3.4 percent for investigational cancer treatments"
So by that source, I was wildly pessimistic.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6...
Cancer isn't an infection and is a million different diseases lumped together.
We could prevent the flu much more reliably if it didn't mutate so much. Will this disease do the same? Maybe. It's very hard to know.
Re the lasting for years, Thailand where I am has gone from 3000+ cases to zero local transmissions. Mostly from basic stuff like masks, testing and quarantine. I hope this can be replicated in other countries.
http://dminder.ontometrics.com/
I only wish the algorithm used to derive the estimates was public/documented somewhere ...
Well, that's one thing you don't need to worry about. Vitamin D is fat-soluble, so any excess isn't excreted in urine (hence the arguments over effective vs. excessive dosage).
Good point. Thanks for pointing that out. I knew about the whole concept of water vs fat but didn't occur to me in this context
Why has Japan, with an older population (median age 47), a tiny island, crowded indoor subways —- has only experienced 900 deaths and never locked down! while some zip codes in New York experiences 2x that amount.
Even state to state the difference is alarming.
And obesity is strongly correlated with diabetes: https://www.diabetes.co.uk/diabetes-and-obesity.html
There is a distinction to be drawn between obesity rates in the US and Japan and that might be part of the answer to your question.
That's a huge problem in medical studies generally.
https://clinicaltrials.gov/ct2/results?term=vitamin+d&cond=C...
At some point, high-quality RCT results will be in.
It is highly likely that Vitamin D isn't saving these people's lives, it's that the folks without vitamin D are older and/or have disease.
Huge inverse correlation between Vitamin D and all-cause mortality -- but almost complete failure of vitamin D supplementation vs. cancer, heart disease and stroke. What?
Turns out that sunlight produces vitamin D -- and a host of other difficult to detect artifacts, which seem to be at the root of the reduction in all-cause mortality.
Seems interesting. Or, carry on -- I'm sure there's nothing to see here, and your pasty-white overweight doctor's advice to avoid sun exposure is right...
I hope you don't mean the advice to use sunscreen when you're going to be outside so long you'd get sunburn without it.
I can assure you, whether it was the intent or not, that the message got out in the 1980s and 1990s that all sunlight exposure is uniformly bad and its only effect is to increase your likelihood of skin cancer, so everyone should avoid it and unconditionally use strong sunscreen for any exposure.
Without that piece of data you have no idea what, if any, difference the supplements were actually making vs. placebo.
That being said, VitD has much fewer potential side effects than CQ (in the recommended dosage)
On this epidemic we should be looking at potential preventative quick gains, especially as the most disrupting solutions are, well, disrupting.
where RCTs are not possible.
References: [0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2998589/
In causal inference, limited causal claims can be made through observational studies (where no control is done), such as retrospective natural experiments [1]. These methods are of course limited by assumptions and by how closely they match reality.
Note: while a controlled experiment is the gold standard, it is not always feasible or necessary. We don't need to do RCTs on parachutes to prove their efficacy for instance. [2]
--
[1] https://en.wikipedia.org/wiki/Natural_experiment
[2] https://www.scientificamerican.com/article/volunteers-jumped...
In the title of this piece, analogizing to chloroquine is irresponsible. A high % of readers will take the message to stay away from D and never read the rest.
I'm glad he has a similar top-level rec as me: Take all measures to avoid deficiency, probably by D3 of 2000-4000 IU/day (I'd prefer 4000). The piece unfortunately fails to make the other most important top-level comment: that all COVID-19 patients should have their D levels tested and more data on D & COVID-19 severity should be published urgently (possibly based on records that already exist). And all clinical trials for COVID-19 should be testing D levels as well.
Overall, this piece is not emphatic enough that vitamin D may significantly help during this COVID-19 crisis.
Several important responses to some of the top material in this piece:
The NYT article dismissing Holick is terrible and not worthy of being linked at the top of this piece. I won't go into the point-by-point criticisms of this article, but it's not worthy of a piece that is supposed to be weighing evidence.
The bullet point claiming the COVID-19 association could still be a fluke does not adequately acknowledge the causal aspects of the evidence: Many RCTs on D supplementation helping viral/respiratory infections (Martineau et al BMJ 2017), D causally affecting rate of aging in roundworms, causal inference model overwhelming supporting D's role as causal, studies on the correlation correcting for age, sex, comorbidities, and reverse causality, and causal mechanistic biological arguments. Some portion of the strength of the correlation seen in the 1000+ patient cases published in preprint studies so far may be due to other causal factors, but the causal evidence so far makes it very unlikely for the full extent of the large effect size seen to all be a fluke.
The piece wrote: "A healthy full body exposure to sunlight can generate 25000 IU of vitamin D in one sitting, without getting burned. 2000-4000 IU daily of D3 supplements will also work." No. People wrongly believing that some sun gives them enough is probably one of the causes of widespread deficiency. From my review, in the "Practical considerations for avoiding D levels that are too low" section: There are several studies showing that even a lot of sun exposure leaves many people with insufficient D levels. For one list of studies see Tsiaras & Weinstock, “Factors influencing vitamin D status” Acta dermato-venereologica, 2011: “Studies in Hawaii (97), South Florida (98), Southern Arizona (99), Brazil (100), rural India (101) and Queensland, Australia (102) found that significant proportions of the study populations had low vitamin D levels despite abundant sun exposure.” For example, in the Hawaiian study, 51% of the 93 young, non-obese adults had D<30ng/ml despite 29hr/week (>4hr/day) in the sun at latitude 21 degrees. The variability in both seasonal sun intensity and daily hours of exposure for any given individual provide yet another reason that testing blood levels would be helpful. These studies show that even those who seem to get a lot of sun exposure should probably supplement if not testing to ensure adequacy.
Also, the bullet point summary in this piece fails to point out the history of the RDA being set too low by statistical mistake. (Which I've updated my review to include. The story is crazy---the original data used to set the RDA would have resulting in 8000 IU/day if it had been analyzed correctly.)