Vitamin D deficiency is extremely common worldwide. Dr. Michael Holick (a leading vitamin D researcher) notes that “about a billion and a half to two billion people” are vitamin D–deficient globally. He has even called it “certainly the most common nutritional deficiency and likely the most common medical problem in the world”. Large population studies confirm this: a recent pooled analysis of 308 studies (7.9 million people) found that ~48% of people have serum 25(OH)D below 50 nmol/L (~20 ng/mL). In practical terms, almost half of the global population is at least “insufficient” in vitamin D. In many regions, 30–50% of children and adults are classified at risk for deficiency.

-Billions affected: An estimated 1.5–2 billion people worldwide have suboptimal vitamin D status. In the US alone, roughly 40–50% of people have levels below sufficiency (NHANES data).

-Widespread ‘pandemic’: Health experts now recognize vitamin D deficiency as a global pandemic. It is especially common in places with long winters or in cultures where people cover their skin, even sunny countries show high deficiency rates.

-Health consequences: Chronic deficiency causes classic bone diseases (rickets in children, osteomalacia/osteoporosis in adults). It’s also linked to many chronic conditions: higher rates of cardiovascular disease, autoimmune disorders, infections, and cancer have all been associated with low vitamin D.

-In short, when 30–50% of a population is vitamin D–deficient, the public health impact is huge (weak bones, higher fracture risk, and possibly higher illness rates).