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Comment by blurbleblurble | Hacker News Reader

Not enough existing research controls for when in the day vitamin D is taken or for other related nutrient levels (K, Mg).

Vitamin D is part of a whole complex network of signaling processes related to (at the very least) regulating circadian rhythms and how is calcium absorbed and used in the body.

I could see how taking vitamin D in the evening would actually be harmful if it disrupts melatonin synthesis. Do existing studies control for this? If they are, they're hard to find.

Until I see vitamin D studies controlling for those things, I take meta-analyses like that with a grain of salt. And I'll keep taking vitamin D in the mornings + magnesium in the evenings when I'm depressed in the winter. It sure seems to help.

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Said as respectfully as I can, it seems like there's a lot of post-hoc justification from the supplement crowd.

I.e. 'Well, no effect was observed because Y wasn't done simultaneously.'

Which isn't to say vitamins aren't under-studied and -prioritized.

But is to say, it feels unscientific to always quibble over experiment design after the results show no effect.

> it feels unscientific to always quibble over experiment design after the results show no effect.

Respectfully, this is exactly what science is. The process of finding potential confounding variables and controlling for them in a new study is critical.

The OP isn’t saying the original study is wrong, or falsified, or whatever, just that it might not account for a particular effect. Someone should study that effect!

There is a lot of untestable post-hoc armchair experiment criticism from the supplement crowd, but this isn’t an example of that!

There are an infinite number of confounding variables in biological systems. Ergo, there are an infinite number of reasons to dismiss any particular study.

OP's suggestions are tightly scoped and proceed from a basis, but there is a point where you're dismissing concrete evidence on the basis of supposition.

I'm not usually motivated by these discussions, but it does seem like it's worth testing the difference between morning and evening for taking something that's related to circadian rhythms.

I've been wondering about melatonin.

It started when I heard about umbilical stem cell injections on the joe rogan episode with mel gibson. I started to look into it, and mesenchymal stem cells seem to really "fix things" that have broken down in your body. The more I read about them, the more I think they're going to be a powerful way of staying younger and fighting aging.

And then I read that melatonin is what regulates the natural generation of them in our body. Hmm.. probably something you shouldn't disrupt.

>I could see how taking vitamin D in the evening would actually be harmful if it disrupts melatonin synthesis.

How would this work? From my understanding, vitamin D blood concentration takes quite a while to build up due to the fat soluble nature, and taking a single pill doesn't cause an immediate spike just like staying inside for an entire day doesn't cause a drop.

Here's a study showing a marked circadian rhythm in serum 25-hydroxyl vitamin D levels. There are actually lots of theoretical papers about this kind of thing, yet somehow so many of these nutritional studies seem oblivious to them or something.

https://pubmed.ncbi.nlm.nih.gov/25788054/

If you dig a little you'll find a similar situation with Mg/Ca/vitamin K/vitamin D. There are lots non-controversial evidence and understanding of the relationships between them, but the nutritional studies on vitamin D supplementation seem all but oblivious to that information.

So that study seems to conclude that the blood concentration of vitamin D varies according to circadian rhythms.

That's an interesting finding, but what I'm saying is that I don't think taking a vitamin D pill has an immediate effect on your body's vitamin D levels. That's why it takes weeks or months of supplementation before you see it reflected in blood tests.

One issue here I'm realizing is in a difference of assumptions... I'm used to taking vitamin D3 drops under my tongue, which I imagine absorb differently than capsules.

But even so, fat soluble substances can get into the blood pretty quickly when you ingest them, well within the timespan of one day.

So I'm not sure if I understand your reasoning. Can you link to a source?

Something I'm reading now that sounds similar to what you're saying is that during supplementation, it takes a while for serum vitamin D levels to reach a steady state. Maybe that's what you're referring to?

Edit: check this out https://www.sciencedirect.com/topics/medicine-and-dentistry/...

> After an oral dose of vitamin D, blood levels begin to rise at 4 hours, peak by 12 hours, and return to close to baseline by 72 hours.

In this article, I take "baseline" to refer to what I called "steady state" earlier in this comment.

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