Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Vitamin D, part 3 – The Evidence

devaboone.com

Post reply on HN
Print view View original

121–130 of 218 posts

Re: Vitamin D, part 3 – The Evidence

#121

Post by ramenmeal »

dcx wrote: post #92

This seems like it might be a little selective. What about these [1] [2] randomised controlled trials that show vitamin D supplementation has an effect on IBS symptoms? Or this [3] double-blinded trial showing supplementation improved sleep quality in people with sleep disorders? Or this [4] one showing improvements in depressive symptoms in overweight and obese subjects? The study cited in TFA is large but only uses…

I think the article addresses those by saying they are the result of publication bias.

Re: Vitamin D, part 3 – The Evidence

#122

Post by lizzard »

Serious question, whenever I read something about a Vitamin D deficiency, or a huge number of people getting tests back as lacking Vitamin D, I wonder -- what determined what the baseline of not-deficient is, and for which population? How were the baseline expectations set?

Re: Vitamin D, part 3 – The Evidence

#123

Post by gojomo »

waterhouse wrote: post #112
bad_user wrote: post #103

Earlier quoted context omitted.

RCTs are high quality, because they are done in a controlled setting, testing against a control group, testing the null hypothesis. RCTs are able to show causality. The problem with RCTs is that they are very expensive, since it involves keeping people in a clinic, so usually RCTs are short term and can only afford to look at surrogate markers. However most often than not, surrogate markers are enough. Also RCTs tend…

> The problem with RCTs is that they are very expensive, since it involves keeping people in a clinic This may be a noob question, but why? For something like a vitamin supplement, can't you just give the study participants a box of their 50 possibly-placebo pills and require them to take one per day? If you're worried about compliance, can't you require them to write down the time each day when they take the pill—or…

They're not all done in a completely-controlled clinic - indeed the 25,000 person study highlighted here, with followup after around 5 years, of course had the subjects going about their daily lives except during original enrollment & occasional check-ins.

But when outcomes are finer-grained than "did the subject die or get diagnosed with a major new disease", or short-term, or need high compliance & regular monitoring, RCTs can become a lot more intense & expensive.

Re: Vitamin D, part 3 – The Evidence

#124

Post by scott_s »

chmod600 wrote: post #73
beervirus wrote: post #64

Earlier quoted context omitted.

A little more thinking may be in order, since the whole point of TFA is that supplementing doesn't seem to do much good.

It has a green check next to "treatment for Vitamin D deficiency". What part of the article says that you should just ignore low vitamin D levels?

"Deficient" is not the same as "lower end of the normal range." If you suspect you are deficient, go to a doctor.

Re: Vitamin D, part 3 – The Evidence

#125

Post by devaboone »

dcx wrote: post #92

This seems like it might be a little selective. What about these [1] [2] randomised controlled trials that show vitamin D supplementation has an effect on IBS symptoms? Or this [3] double-blinded trial showing supplementation improved sleep quality in people with sleep disorders? Or this [4] one showing improvements in depressive symptoms in overweight and obese subjects? The study cited in TFA is large but only uses…

I wrote the blog post. Unfortunately I was not able to include every study on Vitamin D, and had to pare it back to the largest and/or most significant studies. Most of the studies you mention are small and published in obscure journals.

As for my argument, I would never claim that Vitamin D is "a pretty useless vitamin". It is extremely useful, and is lifesaving for people with hypoparathyroidism. But that doesn't mean we should all be taking it. Note that the studies you mention are looking at treating something, not preventing something. Many of the people supplementing are doing it because they believe it will keep them healthy - and this does not appear to be the case. That is more the point of my article. The articles you cite are interesting and hopefully will produce larger trials.

Re: Vitamin D, part 3 – The Evidence

#126

Post by 0-_-0 »

zwaps wrote: post #113
0-_-0 wrote: post #62

So what's the purpose of vitamin D then? It must be important if it was worth evolving white skin over, so why are studies failing to find that important reason?

It is important, it's just that most people do not seem to have dangerously low levels and derive no benefit from supplementation. The article states several times that very low levels of vitamin D are not good.

Isn't a large fraction of the US an UK populations deficient in vitamin D? Doesn't deficiency mean that there's a benefit to supplementation? I thought that at least the correction of deficiency should have showed up in some study.

Re: Vitamin D, part 3 – The Evidence

#127

Post by tchaffee »

0-_-0 wrote: post #62

So what's the purpose of vitamin D then? It must be important if it was worth evolving white skin over, so why are studies failing to find that important reason?

> It must be important if it was worth evolving white skin over

Where is the evidence that we evolved white skin to produce more vitamin D? Light skin in Europe may have evolved as a widespread thing as recently as 8,000 years ago [1], which doesn't support the idea that it was essential for survival in northern less sunny areas. Are there any studies giving strong evidence as to the causation for evolving white skin?

[1] https://www.smithsonianmag.com/smart-news/heres-how-european...

Re: Vitamin D, part 3 – The Evidence

#128

Post by [deleted] »

devaboone wrote: post #109
null_object wrote: post #107

Earlier quoted context omitted.

I’d also like specifics about the “not statistically significant” part - because otherwise there can be a suspicion of cherry-picking the available data. Which I felt, reading parts 2 and 3 of these blog posts, was definitely a possibility.

I tried really really hard to put in all of the most significant studies on Vitamin D. Small, low-quality studies didn't make it in, but the major trials did.

[deleted]

Re: Vitamin D, part 3 – The Evidence

#129

Post by tarsinge »

devaboone wrote: post #19
m12k wrote: post #2

So Vitamin D deficiency is linked to cancer, heart disease, respiratory infection, stroke, diabetes, and death. But taking it as a supplement helps with none of the above. What is a reasonable hypothesis then? That having an active lifestyle that brings you outside in the sun both causes your Vitamin D to go up, and is correlated with better physical health in general?

That is a reasonable hypothesis. Also, people who are very ill are less likely to get outside and get enough sun, so they will develop low Vitamin D. Vitamin D is likely a marker of poor health. (Once the Vitamin D gets low enough, we do see direct harmful effects from it (think rickets in children), and this may contribute to poor health at that point.)

I’m healthy, fit and relatively active (3-4 hours exercise / week, 30-1h walk everyday), and I just tested relatively low in Vitamin D (before winter even started). What should I do?

Re: Vitamin D, part 3 – The Evidence

#130

Post by kebman »

m12k wrote: post #2

So Vitamin D deficiency is linked to cancer, heart disease, respiratory infection, stroke, diabetes, and death. But taking it as a supplement helps with none of the above. What is a reasonable hypothesis then? That having an active lifestyle that brings you outside in the sun both causes your Vitamin D to go up, and is correlated with better physical health in general?

It's a classic case of correlation does not imply causation. As implied in the article, people who are sick, stay indoors. So naturally, when they don't get enough sun from staying indoors, they also get lower levels of Vitamin D. And so that is the correlation. It doesn't mean that a lack of Vitamin D causes illness, or that taking Vitamin D supplements will magically cure those illnesses.
Post reply on HN