To state the obvious; Since there are so many things changing in our lives, it's impossible to know whether the "improvements" you mention were specifically caused (/only) by taking more vitamin D.
In my particular case when I did initial blood test, vitamin D was the only thing critically low. There were few other micronutrients that were just slightly low. I was prescribed high-dosage D-vitamin supplements and was told to touch some grass while out in the sun (computer screen time did not count). In just a month after doing that my overall noticeably improved.
After the wake-up call with vitamin D efficiency I paid more attention to my diet and also having some regular exercise. Improving combination of those gave me my next jump in health improvement. Afterwards, I started using few supplements such as L-theanine with my usual cup of coffee in the morning, I'd like to believe it has given me just a slight boost in focus but it could still just be plain old caffeine. However, I know that some people respond to it a lot stronger so there is certainly variation and is quite anecdotal.
I also experienced this same effect after moving to London (from California) in the winter (very cloudy). I felt so low energy for a solid month, and was constantly feeling unwell. Moreover, I had the strangest "cravings" to bask in the sun (such a weird thing to explain, I've never had such an urge before).
The week that I started to figure out my Vitamin D deficiency, I made sure to get a lot of sun every day (it just started getting sunny in London). I noticed immediate improvements.
Potassium: https://www.famnom.com/nutrient/1092/
But what I found super useful is gut health probiotics. No need to eat them all the time, just when you feel challenged.
I don't want to promote specific supplement products here, but let's just say there is one that helped me enormously.
Resulted visiting a doctor who did a blood test, saw I had critically low vitamin D level (~5 ng/ml). Gave high-dose supplements of 20 000 IU to take every day for up to a month and to touch some grass under the sun :D
After fixing vitamin D I did improve my diet more as well (added more vegetables that fixed few other micronutrients that were just slightly low). Combining that with more exercise gave my next big jump in health improvement. I think my diet is pretty close to typical paleo-type diet excluding fish.
My first comment is that I think this is why we have placebo-controlled double-blind studies.
My second is that I took a multi-vitamin for many years and I recommend caution in their use. For much of that time, when I went to the doctor for my yearly physical I would have elevated AST and ALT liver enzymes which is a marker of liver damage. All tests for typical causes of this (hepatitis, others) came up negative.
Finally my doctor asked if I took a multivitamin. I said yes and she told me to stop taking it. That was about 15 years ago and I have never had elevated liver enzymes since then.
It will show you nutritional holes in your diet like insufficient magnesium, vitamin C, zinc, etc that you can then fill with dietary solutions.
You also get to see what foods have what, it’s interesting. Like how one little prickly pear has 200% of your vitamin E needs.
Do you have a source for this (USDA FDC data and google-fu don't concur)? I'd love to have alternate options for Vit E besides almonds :). It's a fat soluble vitamin, available from nuts and nut oils - vegetable sources are harder to find.
https://www.famnom.com/my_food/294b1d1d-6ca3-47ac-9cd4-bfbd6...
I would, however, recommend improving your diet before loading yourself up with too many supplements. Just add various vegetables and you likely won't need to care about things like zinc, magnesium, iron and few more. I think vitamin D was one of the few micros you usually want to supplement as it's hard to get it high naturally. I am sure HN has some dieticians that know more.
For full multivitamin, I recommend Thorne, which uses the most bioavailable chelated versions of vitamins and minerals. Once you learn how in-bioavailable the vast majority of ingredients in a standard MV are, you will feel sad
You should be looking for citrate or glycinate.
PSA: 48% of people have magnesium deficiencies, the highest of any vitamin/mineral, I'm pretty sure.
https://examine.com/supplements/magnesium/#dosage-informatio...
That said, I think biggest mood/focus/energy difference (besides a nice workout which is also important) for me was getting vitamins and other micronutrients in order. I highly suggest you to do a blood test or two per year for all the common vitamins/micronutrients to see which you need to fix.
For men, I think it is especially important to get magnesium, vitamin D and zinc in order; lack of any will likely affect your testosterone levels negatively which will then screw you up in many more ways.
For example, way back I had critically low vitamin D resulting me in frequently getting sick and having periods of complete lack of energy; fixed that and I did not even get common cold for a long time, also no longer random days with no energy.
You shouldn't overly rely on nootropics, caffeine+l-theanine or other supplements to cover up base deficiencies with your micros.