Hi,

my approach would be to measure my levels and supplement based on that. If the specific metrics are not in the ideal range I'd change my strategy.

Everything else, in my opinion, is guess-work since actual absorption is very hard to measure. As long as the relevant markers are where I want them to be I am happy :)

There are, however, certain combinations that are well established like iron + vitamin C or D3 + K2, or not combining a certain nutrient with others, esp. Zinc or Coffee (polyphenoles) with Calcium or Iron. Since zinc and iron is something to keep in check as a vegan/pescetarian, I adhere to that.

For convenience I take (the few) supplements on my list right before breakfast on an empty stomach - except zinc (which I rarely supplement, though). Most of my meals contain a relevant amount of fat (~30-35%), so fat-solubility is taken care of.

Other than that: Building a resilient and well-functioning digestive tract I'd consider the most important aspect. That would mean fibre, pre- and probiotics, high plant diversity, low inflammatory foods.

Jep. Fat soluble supplements with meals, water soluble supplements with water between meels. I also try to avoid absorption competition (e.g. no Selenium with Vitamin C). And I take "uppers" (like B-Vitamins and L-Tyrosin for dopamin etc.) as early as possible and "downers" (for regeneration and relaxation) as late as possible.

It's a deep rabbit hole an I ended in having eight (in numbers: 8!) daily intake times ... For sure a bit too complicated in the long run (and I will hopefully get back to 5 soon) but the other solution would have been to increase the doses to get rid of my deficits ...

Great question and many considerations:

Vitamin D - take with a meal that contains fat - fats trigger the release of fat digesting enzymes (same for other fat soluble nutrients - EDKA)

Iron - take with vitamin C with a meal to improve absorption - avoid dairy as it binds the iron

Magnesium - I take this on an empty stomach

Zink and Magnesium - take it apart (e.g. zink in the morning and magnesium in the evening as they may compete for uptake)

B-Vitamins - take them with a meal early in the day (to avoid stomach upset and too much energy in the evening)

C-Vitamin - avoid it in the evening as it might keep you awake

Tea and coffee might hinder absorption of several minerals

Fish oil is better absorbed with a 'fatty' meal (so I often take it with vitamin D as recommended above)

B12 is difficult to absorb if there is a lack of intrinsic factor (worse by age) - alternative is to take it sublingual

If this is too much to consider, take your supplements anyway as you will absorb some - it is just not optimal ..... and as Ronald mention below, a well-functioning digestive tract is important. If the digestion does not work, you might be wasting your money on supplements - this includes a well functioning liver. If this is the case, enzymes might increase absorption.