From Dept Health website "What happens if I take too much vitamin D?
Taking too many vitamin D supplements over a long period of time can cause too much calcium to build up in the body (hypercalcaemia). This can weaken the bones and damage the kidneys and the heart.
If you choose to take vitamin D supplements, 10 micrograms a day will be enough for most people.
Do not take more than 100 micrograms (4,000 IU) of vitamin D a day as it could be harmful. This applies to adults, including pregnant and breastfeeding women and the elderly, and children aged 11 to 17 years.
Children aged 1 to 10 years should not have more than 50 micrograms (2,000 IU) a day. Infants under 12 months should not have more than 25 micrograms (1,000 IU) a day."
If your skin is very dark you might want to go for a higher figure than the general recommendation, while staying below 100 micrograms. Many people have suggested that Dept Health recommendations are too low and certainly the level they consider "adequate" is below the level the American study suggests is most beneficial for Covid.
White people can be deficient too, I had low levels myself when I had a test. By the end of winter white people who dont supplement are likely to be deficient.
It is sometimes possible to get your gp to do a blood test and you can test privately, I used this lab myself www.vitamindtest.org.uk/ because my gp didnt consider my level bad enough to do a follow up test.