Marydoll
I have Vitamin D deficiency, so am on prescribed supplements. My body doesn't retain it, due to medications.
Vitamin D toxicity is usually caused by large doses of vitamin D supplements, so if you don't need it, in my opinion, you shouldn't be taking it. Only a blood test can show if you have a deficiency.
I have a healthy diet and do not take anything else. I'm fortunate in that frequent blood tests usually identify any problems.
But over-60s in these Northern climes ARE recommended by the government to take D3. Most people living in the British Isles are D3-deficient from September - March, and if you have dark skin, or cover up, you won't get enough at any time of the year in the British Isles. You would have to take a hell of a lot to overdose. I take 4000 iU / day. D3 acts as a hormone and is crucial for immune response, among other things.