The truth is that in northern latitudes, anyone with dark skin is simply unable to meet their vitamin D intake from sun exposure alone. In certain parts of America, and a lot of Europe, a dark skinned person spending the entire lit part of the day outside buck naked is still not enough to synthesize enough vitamin D to be sufficient. Supplementation or dietary ingestion is necessary.
For me, as a dark skinned person in a northern latitude, my levels were very low. Taking 2000 IU a day did nothing. I had to take 10000 IU a day in order to appreciably raise my Vit D levels. That is what we found after checking with a doctor. I would recommend anyone else do the same. 5000 IU + is typical for people with vitamin D deficiencies. Some doctors even recommend extremely high megadoses to reset your vitamin D intake.