A randomized trial reports an average systolic BP reduction of only 1 mmHg after a mandated 1,000 mg/day sodium reduction. Which critique best explains why sodium reduction alone might appear insufficient in that study?

• A. Studies that reduce sodium always lower blood pressure by at least 20 mmHg in most people; therefore a result of 1 mmHg indicates fraud or fabrication rather than methodological limitations.
• B. Reducing sodium increases plasma calcium directly which counteracts all antihypertensive effects, so sodium restriction must be avoided rather than combined with other nutrients.
• C. Confounding factors such as unchanged potassium/magnesium/calcium intake, poor adherence, baseline blood pressure levels, concurrent antihypertensive medication use, and short follow‑up time may mask the true benefit of combined dietary changes.
• D. Sodium has been proven to have no physiological influence on blood pressure in humans, so any observed differences are random and no further dietary considerations are necessary.

Answer: (C)