Melanin content in people with colored skin offers a high level of photoprotection against the adverse molecular and clinical effects of solar ultraviolet radiation. However, it has a modest inhibitory effect on vitamin D synthesis. Tanning in people with light skin delivers relatively modest photoprotection. 

On the contrary, Sunscreens offer high levels of protection in people who lack melanin. Theoretically, sunscreens can render protection similar to that of deeply pigmented skin. However, this depends on the labeled sun protection factor (SPF), which again depends on how well the sunscreen is applied. Mostly, this will not achieve the desired SPF. 

Interestingly, the threshold dose for vitamin D synthesis is less than that for sunburn, making its synthesis possible with sunscreen application.

Source: Antony R Y. Comparison of skin photoprotection by pigmentation and sunscreens. J Cosmet Sci. 2020;71(4):217-26.