When I was a 6 years old girl I found a rusty machete in a forest I was not supposed to be in. I managed to find my way back to the group of adults frantically looking for me in the parking lot nearby, realized they were looking for me, and decided I did not want to get angry/panicked adults all over me. So I discreetely went back in the forest to build stuff with my new machete. Adults soon found me running down a forest hill full of dead wood and poison ivy; while holding a rusty machete. I panicked when my mom yelled at me so I tried to escape by JUMPING down the slope with the machete in my hand, before deciding to keep running away through the creek that cushioned my fall - because now that I was covered in mud and water I figured they would kill me.
During all of this ordeal, I thought the issue was that I went in the forest and got dirty. The "disappeared for a long time" and the "holding and using a rusty machete" did not register as issues.
Goold luck with your daughter, it did not become better for my parents until I was...Until they stopped knowing what I did. And just as you they were unprepared because my older brother is mostly into being alive and safe.
The person you're answering to didn't say anything about "healthy people who don't currently suffer a specific deficiency". I don't think multivitamins are meant for this population anyway, it's for people who know they're prone to deficiencies or even know they have one specific issue (e.g women and iron, dark skin and vitamin D)
We know that placebo can work even if you tell the person that they're taking a placebo. The placebo effect is so famous that people already expect a benefit from it.
But I guess it varies by individuals so maybe some people would lose it.
I don't think I've seen this suspected correlation receive a lot of credit. A lot of deadly health issues are not correlated to your nutriments intake. Cancer for exemple, thyroid issues, and many others. You would need to take lifestyle into account to even start assessing how multivitamins could potentially increase life expectancy.
Take two groups of people who live active lifestyles in non polluted areas, who don't smoke and don't have any other health issues (including mental health issues because a lot of them are correlated with a shortened lifetime). Give placebos for one of these groups.
This study would help a bit, but would be impossible : we don't have enough people who live this lifestyle and are available for long testings on multivitamins. They may also change their lifestyle, get into an accident, develop mental health issues, travel...Which would poison the results.
I think no one should take multivitamins expecting to live longer. Take them for the other proven benefits - they counteract deficiencies, that's all. My blood tests already show this, I take a blood test before an Iron Supplementation Cure and after, the benefit is clearly visible on the test.
Hmmm, I have no idea how to get or make the placebo pills, I don't have any tools to make them myself, I wonder if my pharmacy or a local lab would accept to do it for me. I might actually do that but I would need to try two cures instead of a random pill every day because I currently start "feeling better" after a few weeks of taking it.
I am actually curious enough to try it but I would need to do it next semester or next year because I would need to also buy or secure enough multivitamins for the year (two cures a year, it would not be a double blind anymore if I get them just before the cure) and since some of them are prescription I'll have to talk about it with my doctor, see if he would prescribe enough and if yes, how long is their shelf life and how I would go to get placebos.
I don't think people take it to improve longevity. I take it because I have periods of times when I can't eat well enough and I can feel myself getting sluggish. Multivitamin actually help me feeling a little better in those periods (it may be a placebo but I would prefer a test on that specifically instead of longevity)
During all of this ordeal, I thought the issue was that I went in the forest and got dirty. The "disappeared for a long time" and the "holding and using a rusty machete" did not register as issues.
Goold luck with your daughter, it did not become better for my parents until I was...Until they stopped knowing what I did. And just as you they were unprepared because my older brother is mostly into being alive and safe.