IANAD, but reasonable algorithm looks like: If you can test, test. Look online what normal levels should be - you'll find several options, pick the higher ones

IANAD, but reasonable algorithm looks like: If you can test, test. Look online what normal levels should be - you'll find several options, pick the higher ones (look for Vitamin D Council for an upper bound recommendation) If you can't test or you test below optimum and you can sunbathe - do that. A lot. It's inherently safe as far as overdose goes. For skin cancer, it's usually worth the risk, and definitely worth it during the pandemic (unless you have specific reasons to think you're higher risk). If you can't test and can't sunbathe... in normal times I'd suggest to supplement except in summer. But in Covid times, I'd go with light supplementation during summer (<1000 UI daily) and higher dosage staring autumn (~2000 UI).