Skin high in melanin is often Vitamin D deficient.
Why? Because large amounts of melanin reduce the skin's ability to absorb sunlight.
This is key because a major source of Vitamin D is exposure to natural sunlight and dark skin requires at least 3-5 times longer sun exposure to make the same amount of Vitamin D produced by an individual with light skin.
Vitamin D deficiency can cause a number of health issues- namely weakened immunity and osteoporosis and has been cited as a potential cause for COVID-19 susceptibility among Black & Brown populations.
Darker skinned individuals should have their Vitamin D levels checked by their physician and, if deficient, take a supplement.