You can request a test to confirm your level of Vitamin D. If you get the test make sure it is the right one! 25 (OH) stays in the blood longer, so this is the more accurate test. (half life of 3 weeks in your blood).
Many experts recommend a level of at least 30 ng/ml ... some actually suggest that 50 ng/ml is recommended.
The scale on the test results is: Interpretive Data: Deficiency: <10 ng/mL Insufficiency: 10 to 30 ng/mL Sufficiency: 30 to 100 ng/mL Toxicity: >100 ng/mL
"The majority of 25-OH vitamin D (25-D) in the circulation is derived from the conversion of 7-dehydrocholesterol in the skin that is irradiated with ultraviolet radiation in the UVB range (wavelength 290 nm to 315 nm).1-5 The extent of vitamin D formation is not tightly controlled and depends primarily on the duration and intensity of the UV irradiation. Levels produced typically reach a plateau within 30 minutes of exposure." [1]
"Vitamin D insufficiency is more prevalent among African Americans (blacks) than other Americans and, in North America, most young, healthy blacks do not achieve optimal 25-hydroxyvitamin D [25(OH)D] concentrations at any time of year." [2]
"The majority of 25-OH vitamin D (25-D) in the circulation is derived from the conversion of 7-dehydrocholesterol in the skin that is irradiated with ultraviolet radiation in the UVB range (wavelength 290 nm to 315 nm).1-5 The extent of vitamin D formation is not tightly controlled and depends primarily on the duration and intensity of the UV irradiation. Levels produced typically reach a plateau within 30 minutes of exposure." [1]
"Vitamin D insufficiency is more prevalent among African Americans (blacks) than other Americans and, in North America, most young, healthy blacks do not achieve optimal 25-hydroxyvitamin D [25(OH)D] concentrations at any time of year." [2]
[1]: https://www.labcorp.com/test-menu/36721/vitamin-d-25-hydroxy
[2]: https://www.ncbi.nlm.nih.gov/pubmed/16549493