Urinary sodium excretion is positively correlated with blood pressure levels across diverse human populations.

Study: The Correlation Between Urinary Sodium Excretion and Blood Pressure in Hospitalized Adult Patients with Hypertension

This study found that people with higher salt in their urine also had higher blood pressure, which matches the claim that more salt excretion is linked to higher blood pressure.

Study: Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Intersalt Cooperative Research Group.

Scientists measured how much salt people pee out and checked their blood pressure — they found that people who pee out more salt tend to have higher blood pressure, especially as they get older, across many different countries.

Study: Study on the Correlation between Urinary Sodium and Potassium Excretion and Blood Pressure in Adult Hypertensive Inpatients of Different Sexes

This study found that people who excrete more sodium in their urine tend to have higher blood pressure, which matches the claim. It looked at men and women with high blood pressure and saw the same pattern in both.