Which process synthesizes vitamin D in the body?

• A. Synthesizes vitamin D through sunlight exposure.
• B. Produced by the thyroid gland.
• C. Primarily from dietary fats.
• D. Requires water for activation.

Answer: (A)

Vitamin D is produced in the skin when the body is exposed to ultraviolet B light from sunlight. UVB converts a cholesterol derivative in the skin (7-dehydrocholesterol) into previtamin D3, which then becomes vitamin D3. This vitamin D is carried to the liver, where it’s hydroxylated to calcidiol, and then to the kidneys to form calcitriol, the active hormone. The thyroid gland doesn’t synthesize vitamin D, and while vitamin D is fat-soluble and needs fats for absorption from the diet, the body’s synthesis relies on sunlight exposure, not dietary fats. Activation occurs through enzymatic hydroxylation, not through a requirement for water.