This is a refreshingly balanced and honest analysis of Vitamin D studies.

The strongest evidence for Vitamin D is in people who are severely deficient. Bumping up to a normal range can provide some improvements.

The health influencers started noticing that the Vitamin D studies coming out weren't matching their original hype for Vitamin D, so many pivoted to trying to make claims that most people are severely deficient and just don't know it, which provides a convenient out to dismiss the studies that didn't pre-filter for people who were severely deficient. You can find waves of people on social media repeating the idea that almost everyone is Vitamin D deficient and encouraging high dose supplementation still.

Speaking to a doctor who runs Vitamin D labs as part of her annual physical screening process, she's now actually seeing more people who have excess Vitamin D than too little Vitamin D. Upon followup she discovers that patients have listened to a podcast about Vitamin D and started taking it regularly, unaware that they're pushing their levels into the range where it can start doing more harm than good.

Vitamin D is tricky because it lasts for a very long time in the body, which means steady-state supplementation can take a very long time to stabilize. I suggest anyone supplementing for a long time get a blood test, which can be ordered without your doctor if you can't get your doctor on board.

On another topic: Fish oil has also gone through a similar cycle of being hyped up based on early results, with higher powered follow on studies showing much less interesting results.

You keep showing up under articles about vitamin D and keep telling that more people have excess than insufficient vitamin D levels without presenting any data whatsoever.

We're among plenty of inside-dwelling nerds here. Do the test. Don't listen to folks like the parent, don't let yourself be discouraged; check your blood level and act on it if necessary, it's fast and cheap. I even had a test done at my home, you can schedule that online these days! You're much more likely to be severely deficient than have it in excess (it's quite hard to get to toxic levels anyway, you'd need to be really irresponsible about it) and once you confirm that, supplementing can help you tremendously with plenty of mental issues you may be experiencing. It won't fix you up, but it can make it possible for you to fix yourself up in the first place. And if the test shows you have adequate levels already - good for you.

(and if you're too depressed to even arrange the test, it may make sense to start supplementing blindly - but don't exceed ~10K IU D3 daily and make sure to stop after 2-3 months tops. Hopefully at that point it'll be easier for you to finally do the test to know whether to continue or not; don't keep taking high doses blindly, toxicity is hard but not impossible to achieve and you really don't want to be suffering from it. You almost certainly won't reach it with 10K IU when starting from deficiency, but it you happened to be on the high side already at the start it could be dangerous when prolonged)

My family runs a blood analysis lab in Belgium for which I wrote some of the statistics gathering software.

The thresholds for 25-OH vitamin D: <20 ng/mL → deficient, 20–30 ng/mL → insufficient.

When I looked at all 1738 blood samples that had their Vitamin D tested between Feb 1, 2020 and Mar 13, 2020 (We were looking into the link between Vitamin D and COVID-19): The median (P50) was 20.1 ng/mL and the average was 22.4 ng/mL. Standard deviation: 11.24 ng/mL Half the samples were deficient, and the next 20% was insufficient.

Coming out of winter in Europe in a country with limited sunshine: most of the population is deficient in Vitamin D.

Histogram: https://files.catbox.moe/p785wx.png

The Mediterranean diet itself has a lot of health benefits interrelated with the ones claimed about fish oil.

But just as a human experience, the first time I ate cod livers, it was hard to accept. Then I started spreading them on toast for breakfast, and realized that they were quite delicious, but very very much an acquired taste (and I eat almost everything).

As far as Vitamin D, there does seem to be a correlation between deficiency and severe coronavirus disease

https://www.mdpi.com/2075-1729/15/5/733

[edit] to say, I love chicken and cow liver, but it took awhile to get a taste for fish liver. Pork liver, however, is putrid. I don't think I could eat that again.

Seemingly any decent way to tune in a steady-state supplementation involves multiple iterations of the "get blood test, adjust dosage, repeat" loop

On the other hand, when our body synthesizes Vitamin D itself it seems to regulate that process to prevent overdose. So I've just settled on supplementing in the winter based on my best estimate of the correct dosage, then let my body do its thing in the summer. No issues so far, and supplements have had a major impact on my fatigue/energy/depression levels in the winter

On a slight tangent, if people are unaware, you can pay for and get just about any lab test without a prescription in the United States.

Baby aspirin was overdone too. Interestingly, the fish oil hype cycle has a much longer timeline if you consider the popularity of cod liver oil once upon a time.

The moral of the story here is just to do bloodwork on a regular basis (absolute bare minimum once a year) and respond accordingly. I take some supplements like vitamin D, but I only take what is empirically measurable. If I can't quantitatively measure the outcome, then there is no value and it's a woo woo solution. This isn't always going to be the best advice, but a vast majority of times it will be.

> The health influencers started noticing that the Vitamin D studies coming out weren't matching their original hype for Vitamin D, so many pivoted to trying to make claims that most people are severely deficient and just don't know it, which provides a convenient out

Not really. It isn't possible to be severely deficient in vitamin D without knowing it. By definition, if you are severely deficient in vitamin D, you have rickets.

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It's pretty safe to assume all hyped supplements are pointless. Being generally active and eating fruits/vegetables is like 80% of the work for being healthy.

> almost everyone is Vitamin D deficient

This was the red flag that made me realize it was BS early on. If everyone is deficient, then it must not be that important.