Some people may be responding poorly to the supplement, especially at high doses and low calcium. Direct blood test for status would help.
Makes sense. This is often how the body works. You should get enough of <nutrient> but having more than needed doesn't turn you into a superhero (but it can be poisonous).
Not say that lends me too much authority on the matter, but many of the biological effects of D3 are pretty poorly understood, still. Simplifying a bit, this can be chalked up to the fact that it's roles in molecular networks across the systems are myriad, and of these, many of its (downstream) effects seem -- and, if not, are -- contradictory. (To the initial point, in it's bioactive form, it's classified as a hormone.)
At high dosages, typically what's found it many OTC supplements (5-10K IUs vs 500 IU daily allowance), there is evidence that it facilitates significant bone resorption.
So not only does it not strengthen bones, D3 actively makes it more brittle. Typically, this is linked to inadequate calcium & phosphate minerals to match the excess D3 (and these minerals in excess introduce additional problems of their own).
I didn't cite literature here but it is readily available & abundant (But I can pull some if anyone would like). And, within it, there is a glaring lack of consensus. And hence, why my language is couched in so many conditionals.
Another question for you, does supplementation work as intended when our diet is insufficient, or is it just a gimmick? I've always wondered about this. By work, I mean, if you were to have a blood test in two parallel trials, one where you supplemented but had a crappy diet and another where you ate the "perfect" diet that supplied the daily IU needs, would the blood work show equal amount of each mineral/vitamin/etc in both cases?
>Vitamin D increases absorption of calcium and phosphate in the intestinal tract, leading to elevated levels of plasma calcium, and thus lower bone resorption.
Essential vitamins are clearly important to multiple health and fitness pathways. But identifying which specific pathways, results, and mechanics has value.
One of my favorite articles. Vitamin D supplementation has a very poor track record of doing anything positive. It’s very likely that most of the studies attributing benefits to vitamin D and correlations between serum vitamin D and health are because it is a surrogate marker for getting sunlight, which may be the real health improver. When we supplement with D in properly controlled studies, the health benefits disappear.
I'm not vegan and I actually take Vitamin D3 supplements, but wanted to point out the flaw in assuming that everyone is in the same bucket as me.
Generally speaking, interesting to consider that Calgary is a fairly northern city and they say more northern people get less natural VitaminD from sun exposure... So even in a generally vitaminD short populace the results are showing no stronger of bones. I say all this iirc, not from specific scientific sources...
tl;dr there are homeostatic mechanisms in place in calcium metabolism that result in a "counterintuitive" reduction in the active metabolite with supraphysiologic supplementation. Also, this is actually in line with prior work, though the authors don't mention any of it until the discussion at the end, and then only two papers. In about 5 minutes of searching, I found papers going back to 1995 suggesting the same thing.
I take Vitamin D, Calcium, and alendronate (Fosamax), and when the sun is out, I go out for a while without sunscreen.
My last DXA (2.8 years ago) had a Z-score of -2. I'm only in my 40's, so I don't have a T-score.
I don't really care about the validity of this study. I just know I have to take Vitamin D and Calcium supplements regularly, and Magnesium less often, but regularly.
I mean no one really expects vitamin d by itself to improve bone density. It’s but one step in the process.
1) It probably easier to measure density than strength. Additional measurement noise could mean the strength difference is not statistically significant while the density difference is.
2) The relationship between density and strength is probably not a simple 1:1 linear function. For example a 10% bone mass reduction may only result in a 1% strength reduction. Therefore one many be statistically significant while the other is.
Likely is is a combination of factors like this. Things are rarely simple in the lab.
"mean [SD] age, 62.2 [4.2] years"
1. Stimulus: ie lifting heavy, nutrients to support hormonal response
2. Materials: ie Calcium / minerals
3. Rest: ie Sleep, recovery time etc.
I would expect any isolated intervention to find lackluster results despite considerable results in conjunction.
Current advice is don't take more than 100 micrograms per day.
> At trial end[...]
> mean percent change in [radial] volumetric BMD of −1.2% (400 IU group), −2.4% (4000 IU group), and −3.5% (10 000 IU group).
> mean percent change [...in tibial volumetric BMD] of −0.4% (400 IU), −1.0% (4000 IU), and −1.7% (10 000 IU).
> There were no significant differences for changes in failure load (radius, P = .06; tibia, P = .12).
The bone density decreases may look minor on paper but look at it this way: it’s quite possible that a very large cohort of elderly and middle aged people concerned about their bone health (potentially because they were told they have reason to be concerned) have been paying a lot of money annually to actually worsen their situation. That sucks.
One of the findings (there's a summary somewhere): https://epic.iarc.fr/highlights/vitamindcolorectal.php
>Main Outcomes and Measures: Co-primary outcomes were total volumetric BMD at radius and tibia, assessed with high resolution peripheral quantitative computed tomography, and bone strength (failure load) at radius and tibia estimated by finite element analysis.
>Conclusions and Relevance: Among healthy adults, treatment with vitamin D for 3 years at a dose of 4000 IU per day or 10 000 IU per day, compared with 400 IU per day, resulted in statistically significant lower radial BMD; tibial BMD was significantly lower only with the 10 000 IU per day dose. There were no significant differences in bone strength at either the radius or tibia. These findings do not support a benefit of high-dose vitamin D supplementation for bone health; further research would be needed to determine whether it is harmful.
Headline is not imprecise according to above-cited Conclusions and Relevance.
No, aladoc99 is right, because the study doesn't compare against 0. So you don't know if 4000 and 10000 improve strength compared to 0, only that they don't compared to 400. It's not a hill that someone should die on, though.
And thus we have ourselves a quandary, but truth isn't diminished by the practical limits of safe experimentation. We don't have to lie just because.
> it would be harmful to the subjects.
That doesn't make the title precise or the observation inapt.