They tested 11 different measures. Only 3 of those tests showed significance, but after they corrected for multiple testing the significance of 2 of those disappeared. Only 1 test remained below the significance threshold.
This is on a set size of about 500 children who completed the study, randomized to the two groups.
The only measure that remained statistically significant was visual memory. If you look at Figure 2 it's not even clear that there was a trend toward improvement because everything is so scattered, including a couple measures that were trending worse with higher Vitamin D levels.
This study isn't very convincing. It's a classic p-hacking trick to include many different smaller tests so if one of them pops up as an outlier you can claim that something was significant.
I point this out because there are so many known factors both positive and negative that contribute to increased 'cognitive performance' it is impossible to account for all of them, even within a randomized trail such as this. People are weak to assumptions when it comes to correlation.
1. Yes, vitamin D actually controls a lot of bodily functions it’s very easily set aside as not a “main” factor when in reality it actually controls a lot
2. This study was done on women in Denmark only which isn’t a great study subject considering Denmark doesn’t get a lot of sun to begin with so most of these women would already start at very low levels
3. This doesn’t directly correlate to women of color because WOC need higher dosage of vitamin D than white women do. The general range of “good” level of vitamin D that doctors tend to use is related to studies results gotten from white people when in reality brown and black people need way more for their range to be at a normal place.
1. They measured maternal vitamin D before supplementation began. They explicitly adjusted for these preintervention levels.
2. the two groups started at essentially the same vitamin D levels.
3. They specifically tested whether baseline vit D status changed the effect of supplementation
For my own point: in this study they have like 22 test values but still use the 95% confidence interval. Even on random data there will be a significant result like a third of the time so I think it's easy to interpret these result as more definitive than they are. Not that it's a bad study though (no study will be everything, baby steps like this are important in science).
> Covariate-adjusted analyses of standardized scores (mean [SD], 0 [1]; higher values indicating better performance) showed positive associations of high-dose vitamin D3 with verbal memory (β = 0.17 SD; 95% CI, 0.03-0.32 SD; P = .02), visual memory (β = 0.24 SD; 95% CI, 0.06-0.42 SD; P = .01), and flexibility or set shift (β = 0.19 SD; 95% CI, 0.01-0.37 SD; P = .04); however, high-dose vitamin D3 was no longer associated with flexibility or set shift after multiple test correction.
Generally, when a study is done in the US - no one will ever question the location. The moment the study is outside the US, "not US so not generalisable" questions always arise.
As they stated, it is because the population of Denmark is very homogenous, as opposed to the US. If you are trying to make a generalization that applies to a range beyond just white people, having Denmark as your sole sample is clearly flawed.
Along the same lines, picking Japan for the purpose of generalizing to wider racial/ethnic groups would also be a bad idea. Not because their research is untrusted/considered non-reputable (it is quite the exact opposite), but because their population is too homogenous.
> As they stated, it is because the population of Denmark is very homogenous
If you know about vitamin D, you'll note that sun exposure is one of the primary reasons location matters for this study. It would be similarly relevant if they only studied students in Miami or southern California.
Essentially: sun exposure helps you create vitamin D, and so you shouldn't naively generalize this study to other lines of latitude
It is probably a logistical nightmare to do a study of this sort in multiple countries and regulatory systems simultaneously.
It's just an important factor - if you live much further south or spend a lot of time outdoors, your target dosage will be different than someone in _Denmark_.
Studies everywhere are now being scrutinized for the participant cohorts because it is now widely recognized that biological differences exist between different groups. Some medications for example aren’t sufficiently studied for effects on women vs men and are being reviewed.
Plus, studies in US are less scrutinized because researchers are aware of the need for a diverse cohort and you are more likely to get one in the US vs elsewhere.
Spain have lower levels of vitamin d than Denmark.
In places like Spain only some “premium” milk gets this treatment.
That same mutation made them vulnerable to the levels of sunlight at lower latitudes, susceptible to sunburns, etc.
First, that's only true for about 4 months of the year. Second, people cooped up in offices in China, India, and the US don't get a lot of light either. In fact I'd bet the better work-life balance in Denmark means people actually do get more light there because they spend more of their evenings and weekends outside instead of in the office. Office buildings in Denmark also tend to have much better sunlight by design.
You can probably have the same results in the New England area of the USA, no? Even NY with 10mil people?
3. Okay, and?
this is right there in the abstract, isn't that the entire game?
If there were a connection then I would wager that there are more significant factors, since I have seen or heard of no evidence to assume those in sunnier climates have better verbal and visual memory.
The results of this study seem to show no significant correlation, anyhow.
(I realize this is a frought topic, so please hold the race science bullcrap replies or the over-reactions in the other direction. I am not a believer in hard biological determinism or "race science," but I also don't dismiss the existence of variations. As with everything else in population genetics and biology, any variations that do exist probably have more than one cause.)
If there's any truth to this, it might be further compounded as people with darker skin spend more time indoors in the modern world. If you have darker skin you need, as far as I know, more sun to make vitamin D, which normally is not a problem if you're outdoors near the equator.
I think a combination of good policies and ideally some preexisting wealth will trigger this upwards cycle.
And even clothing.
I don’t think clothing is that big a factor because all humans in hot environments adapt and very little survives in the archaeological record. Many populations lived in heavily forested jungles where they was little sun exposure and those in deserts used stuff like Otjize for sun protection. Given all the ethnographic reporting from the age of exploration, tons of that clothing was probably made of feathers, cordage, bark, and other materials we wouldn’t even think of using for clothing.
They flags their own post hoc status, reports modest effect sizes, and applies some multiple-comparison correction. That makes the rhetorical sleight of hand harder to spot, because it's buried inside otherwise careful looking work.
The statistics are shit. They applied Benjamini-Hochberg FDR correction within cognitive domains, not across the family of 11 functions. That choice is what produced the headline "memory survived correction."
Watch what happens with the actual numbers. The two "winning" functions, verbal memory (p = .02) and visual memory (p = .01), both sit inside the memory domain — which contains exactly those two functions. BH within a 2-member family barely adjusts anything: the most lenient threshold is just 0.05, and both p-values are already under it, so the q-values come back at .02 and .02. The correction was toothless by construction, because the two hits happened to fall in the same tiny domain. A reviewer should have made them show the whole-family result side by side. The fact that they didn't is the tell. And there is much more that could be criticized in the same manner across the whole thing.
And then the observational data fail to corroborate the supplementation finding. The authors explain the mismatch via trimester timing of exposure, which is plausible, but the equally plausible reading is that the RCT hits are fragile, or that, more probably, it's not a real effect.
And even if there was an effect, it's so small and weak and NOT proven by even this data, that the recommendation for supplementation is not warranted at all. At best, this single study with their focus on recreating this effect is the only defensible conclusion. And yet they recommend supplementation.This is pure bias and D-vitamin cult babble once again.
The conclusion, based on the actual data, is: in a vitamin-D-sufficient cohort, high-dose prenatal D3 was not associated with offspring cognition on any whole-battery-corrected measure.
I hate this so much because it's stupidity like this that shows that science is not worth paying attention to, because the scientists basically lie through their teeth, at least from my perspective, where truth is something that is verifiable and relates to something real.
At any rate their main marker for intelligence showed an impressive p=90%, so whatever cognitive effects were present they've not made them any smarter (at 10).
Maybe it's the high dose vitamin, maybe it's because one cohort was skewed one way on the socioeconomic spectrum, maybe it's something else entirely. More evidence would be needed imo to confirm Vitamin D3 has a direct contributor to cognitive performance as the research portrayed.
The main trick behind randomized control trials is that you can disregard factors like this because these effects would be randomly distributed as well.
If a study is going to draw debatable conclusion after 10 years on high dose Vitamin D during pregnancy, I'd expect at least some comment in the study on the general socio economic landscape and grouping.
Regardless, this study looks like a sham to me.
it is -exactly- like Linus Pauling and Vitamin C cult in the previous century
Vitamin D is very important
Too Much is as bad as Too Little
The "RDA" is too low at 600IU and should have been changed to 2000IU decades ago
It can help prevent certain diseases and illnesses
It CANNOT cure any known disease or illness once afllicted
It makes you wonder how much of what we accept as "normal" afternoon brain fog or tech burnout is actually just our biology reacting to this massive behavioral shift and lack of natural light.
It's one huge perk of working from home. Lying down for 20 minutes makes the rest of the day much more pleasant and productive.
Check the CO2 levels in your office. They can get ridiculously high indoors when humans gather in the same room. It's not dangerous, but it makes people tired, they stop taking initiative, and less creative.
The natural rest position of the human eye is to focus at the infinite. Focusing on closer objects like books or screens requires a constant effort (we don't feel it).
The eye simply adapts and elongate to relieve some of the strain. Wearing corrective lenses further amplify the process.
If you want your kids to have perfect vision they should spend a lot of time playing outside, until early adulthood.
Clearly there's some significant environmental factor, and constantly focusing at short distances and/or getting no bright light exposure are the two obvious candidates (in other words, being inside all the time)
Whatever we're doing that isn't what they're doing is not normal.