Restricting sodium intake leads to which change in water retention?

Restricting sodium intake leads to which change in water retention?

• A. Decrease water retention
• B. Increase water retention
• C. No change in water retention
• D. Water retention fluctuates with urine output

Answer: (A)

Water balance is driven by sodium because water follows sodium osmotically. When sodium intake is restricted, there’s less sodium in the extracellular space to pull water in, so extracellular fluid volume decreases. The kidneys also excrete more sodium relative to intake, and since water follows sodium, overall water retention falls. So the net effect is a decrease in water retention. The other choices don’t fit this relationship: increasing sodium would tend to increase water retention, while “no change” or fluctuations with urine output don’t reflect the steady, net reduction seen with sodium restriction.

Water balance is driven by sodium because water follows sodium osmotically. When sodium intake is restricted, there’s less sodium in the extracellular space to pull water in, so extracellular fluid volume decreases. The kidneys also excrete more sodium relative to intake, and since water follows sodium, overall water retention falls. So the net effect is a decrease in water retention. The other choices don’t fit this relationship: increasing sodium would tend to increase water retention, while “no change” or fluctuations with urine output don’t reflect the steady, net reduction seen with sodium restriction.