Whilst I agree that there's a lot of people with D3 deficiency (at least during winter), it's also worth being careful of taking too much D3. Typical signs of too much D/D3 are nausea, loss of appetite, more frequent urination, thirst, weakness, confusion or brain fog.

It's worth being aware of that as the recommended limits for vitamin D are laughably too small, so it's common for people to take much larger amounts. I believe that 4k IU is considered a safe adult dosage.