The only thing that matters is the serum level. Testing your blood levels is like closing the feedback loop. Levels too low? Increase dose. Too high? Back off.
Genetic testing isn’t necessary or even really helpful. Just get the basic serum levels tested and adjust accordingly. It really doesn’t have to be complicated.
first of all, low/high levels have a cause. if it's nutrition, yeah, you're right, just measure and correct.
but you come to the conclusion that's nutrition with zero evidence supporting it, and that's annoying as hell, because it's basically shunning the door for people with real conditions that could live 10x times better if only someone would have used a more rigorous method of inquiry instead of 'just nutrition lol'
it doesn't have to be complicated, but it still have to be rigorous.
Measuring serum levels is sufficient to detect and work around genetic absorption defects. No one needs to get separate genetic testing if their serum levels are within range.
After doing so, my colds have been far less severe then in the past. What made me go to such lengths testing myself was that I thought I was doing everything right and yet got pneumonia two years in a row.
So aside from testing your blood serum levels you should consider a genetic test to see how well you absorb vitamin d. You may benefit from above average dosage (consult your dr. Ymmv)