I'm actually rather annoyed by the recent trend of basic things like "go touch grass" or "go exercise every day" or "eat more fiber" being scientifically validated, because it's stripping away any and all excuses for me not going outside/exercising/eating well/etc.

Like damn, I knew I was supposed to do such things already, but it's the difference between mom saying to eat your veggies vs. mom slamming down a stack of scientific paper about why not eating veggies will literally kill you or whatever.

If it helps, you can just take a vitamin D supplement and stay inside, avoiding some major health risks like skin cancer and death by vehicular accidents.

Sunlight does way more than let the skin convert this specific chemical. You could look up photobiomodulation, for example.

Sure, get a sun lamp.

Get an under-desk elliptical, vit D oil drops, bake bread with 50% wheat flour replaced with almond/coconut/sunflower/pumpkin/etc meal.

Wham, unhealthy lifestyle eradicated at almost no behavioural cost.