[mschuster91]

Vitamin D deficiency (and while we're at it, B12 deficiency and iron deficiency) are real deficiency issues that have risen in numbers across Western societies for quite the time now - IIRC, a large contributor is our change in diets and living habits.

Basically, we're spending far less time working out in the open so our body doesn't generate vitamin D on its own in sufficient quantities, and the trend towards highly processed, nutritionally inflexible diets on one side and vegetarianism/veganism on the other side leads to a whole host of malnutrition issues.

Unfortunately, the "malnutrition" levels in bloodwork are mostly calibrated on white European males... so similar to BMI [1] and a few medications and diseases [2], there is a "vitamin D paradox" in Black people who seem to not be that sensitive to lower vit-D levels than White people [3].

Human bodies and genetics are fascinating, even if you're not an expert in it.

[1] https://pubmed.ncbi.nlm.nih.gov/9877251/

[2] https://academic.oup.com/ehjcvp/article/8/7/738/6644872

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5954269/