Decreased vitamin D binding to VDRs can lead to which of the following regarding the renin-angiotensin system?

• A. Decreased renin activity
• B. Decreased blood pressure
• C. Decreased aldosterone production
• D. Increased renin activity leading to hypertension

Answer: (D)

Vitamin D–VDR signaling normally keeps renin expression in check. When binding to VDR is decreased, this inhibitory effect is lifted, leading to increased renin activity. More renin drives more angiotensin II and aldosterone, causing vasoconstriction and sodium-and-water retention, which raises blood pressure. So the result is increased renin activity leading to hypertension. The other options imply lower renin or lower blood pressure, which doesn’t fit this mechanism.