Vitamin D insufficiency may account for almost 90% of Covid-19 deaths
It's unfortunate that it is not simple to get regular tests for vitamin and mineral deficiencies. The whole process seems to be stuck behind the doctor appointment firewall. This might be one of the reasons why Theranos was so readily believed. As the quantified self movement that gained popularity around the same time showed, there's an appetite in certain segments of the population for this type of testing and tracking but the process isn't very transparent and often expensive due to it being a profit center. Make it a simple yearly subscription where  you can stop in at any time at a clinic like a CVS Minute Clinic, get a blood sample drawn, and then get your results a couple of hours later. Maybe a limit of once a month or once every other week depending on your needs. Only if something is out of standard range would you need to involve a doctor. It would also be good for your next annual checkup to have an entire year's worth of such data.