Vitamin D

topic

Vitamin D is a fat-soluble prohormone — synthesized in the skin from UVB light exposure or obtained from dietary sources (fatty fish, fortified foods, egg yolks) — that functions as a nuclear receptor ligand regulating the expression of over 1,000 genes involved in immune modulation, calcium homeostasis, bone metabolism, muscle function, cardiovascular regulation, insulin sensitivity, and neural function. Deficiency (serum 25-OHD below 20 ng/mL) affects an estimated 40–50% of adults in the developed world.

Role

Vitamin D deficiency is the most prevalent micronutrient deficiency in the developed world and the one with the broadest spectrum of health consequences — yet it remains chronically underdiagnosed because its symptoms (fatigue, muscle weakness, low mood, frequent illness) are non-specific and are attributed to other causes. The modern indoor lifestyle, sunscreen use, and geographic latitude place the majority of the world's population in a state of chronic vitamin D insufficiency that impairs immune function, bone density, cardiovascular health, insulin sensitivity, and mood regulation simultaneously — a compound health deficit addressable by a supplement costing pennies per day that most people are not taking because they were never told they likely need it.

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