Vitamin D Deficiency

Vitamin D is a fat-soluble nutrient essential for calcium homeostasis and bone metabolism. Deficiency of this beneficial substance can lead to nutritional rickets in children and osteomalacia in adults. In the 1930s, North America began fortifying milk with vitamin D to eradicate dietary rickets in children. The recommended daily intake for adults ranges from 400 to 800 international units (IU). However, subclinical vitamin D deficiency remains prevalent worldwide, affecting up to 1 billion people in both developed and developing countries. Subclinical vitamin D deficiency is linked to osteoporosis, increased risk of falls, and fragility fractures. Recent observational studies have shown a potential correlation between vitamin D deficiency and cancer, cardiovascular disease, diabetes, autoimmune diseases, and depression. The optimal blood concentration of vitamin D remains controversial. According to the 2019 Endocrine Society guidelines, vitamin D sufficiency is defined as having a serum total 25-hydroxyvitamin D level greater than 30 ng/mL (50 nmol/L). Vitamin D insufficiency is defined as having a total 25-hydroxyvitamin D level between 12 and 30 ng/mL (30 to 77 nmol/L), while vitamin D deficiency is defined as having a level below 12 ng/mL (30 nmol/L).