Is 4000iu safe to take daily?
It sits at the upper level UK guidance sets for adults from supplements. That makes it the strong end of normal rather than excessive, but it is worth having a reason for it.
Do most people need this much?
No – 1000iu is the usual everyday choice for topping up through the winter.
Can I take it with other supplements?
Check them for vitamin D first. It appears in multivitamins, cod liver oil and calcium products, and it accumulates in the body.
Is there a vegan option at this strength?
Check the individual product. Most D3 comes from sheep's wool, and the lichen-derived vegan version is stocked at lower strengths.