So what's the ideal amount of sun exposure to produce enough for a white guy at 45 north? Is there anywhere reputable that calculates this kind of thing?
With sun exposure, the book recommends the following. Go sit in the sun on a sunny day, until you get a mild rose burn. How long does that take? Divide that time over a week, and you're safe. This rose-burn time depends on the time of year, how high is the sun in the skye? How clear is the skye? What is the time of the day? So this value changes a lot for people in norther Europe, compared to people living in Africa.
This is sound advice, but isn't there a chicken and egg problem right now? We're in a significant part of the pandemic, which I would imagine (assumption) that "routine" tests such as that may not be easy to come by. While at the same time there is notable evidence that VDI is prevalent in severe cases. By the time you get an answer to know the base line, it seems like it would be largely too late to make a possible difference in the short term?
Is there a "safe" amount you could increase it without knowing your base line?