Prevalence of Vitamin D Deficiency and Its Associations with Skin Color in Pregnant Women in the First Trimester in a Sample from Switzerland concludes "In the most parsimonious model, women with dark skin color were statistically significantly more often vitamin D deficient compared to women with light skin color..."
Similarly, Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes puts forward that:
The melanin pigment absorbs ultraviolet radiation (UVR) and protects
underlying skin from damage caused by UVR. It also reduces the UVR
available for vitamin D synthesis in the skin. It has been shown that
the white-skinned population of the UK are able to meet their vitamin
D needs with short, daily lunchtime exposures to sunlight.
Results show that to meet vitamin D requirements, [Fitzpatrick] skin type V [(brown)]
individuals in the UK need ~25 min daily sunlight at lunchtime, from
March to September. This makes several assumptions, including that
forearms and lower legs are exposed June–August; only exposing hands
and face at this time is inadequate. For practical and cultural
reasons, enhanced oral intake of vitamin D should be considered for