It is strongly recommended to not conduct, fund, or publish research studies that use spot urine samples with estimating equations to assess individuals’ sodium (salt) intake in association with health outcomes: a policy statement of the World Hypertension League, International Society of Hypertension and Resolve to Save Lives

**Background:** Reducing dietary sodium is estimated to be one of the most effective and cost-effective population health interventions. The WHO recommends reducing dietary sodium to less than 2000 mg/day in adults. A meta-analysis of three randomized controlled trials reported that reducing dietary sodium from approximately 3650 to 2700 mg/day was associated with a 26% decrease in cardiovascular disease (CVD), with a linear association between sodium intake (2300–4100 mg/day) and CVD. Similarly, a meta-analysis of cohort studies using multiple 24-hour urine samples showed a linear association between sodium intake (1846–5230 mg/day) and CVD, with an 18–27% CVD decline per 1000 mg decrease in sodium. Despite this evidence, controversy has persisted about whether lowering sodium below 3000 mg/day may increase CVD, driven largely by studies using spot urine samples with estimating equations.

**Methods:** This is a policy statement issued by the World Hypertension League, International Society of Hypertension, and Resolve to Save Lives, supported by 21 other health organizations. The statement reviews the evidence on the validity of spot and short-duration timed urine samples with estimating equations for assessing individual sodium intake and their use in studies of health outcomes. The authors examined validation studies, methodological concerns, and the impact of these methods on disease association findings.

**Key Results:** The paper identifies several critical problems with spot and short-duration timed urine samples: (1) Validation studies repeatedly demonstrate both large systematic and random errors compared to 24-hour urine collections, with error increasing at higher and lower than average sodium intake. (2) Spot urine estimates are not reproducible within individuals. (3) Sodium excretion in short-term samples is influenced by many non-dietary factors including hydration status, body position, time of day, caffeine, neurohormonal activation, cyclic aldosterone changes, cardiac and renal disease, and diuretic use. (4) The estimating equations used to convert spot urine sodium to estimated 24-hour sodium incorporate risk factors such as age, gender, BMI, and urine creatinine (correlated with muscle mass) that are independently associated with CVD and mortality. When these formulae were used instead of measured 24-hour urine sodium, linear associations with total mortality were changed to J curves. In one study, when formulae were used instead of multiple 24-hour measurements, the linear association with blood pressure was also changed to a curve. Furthermore, the formulae showed associations with blood pressure and mortality even when a constant sodium value was entered, demonstrating that the formulae themselves produce spurious associations independent of dietary sodium.

**Clinical Implications:** The statement makes three core recommendations: (1) Researchers should not use spot urine samples with estimating equations to assess individual sodium intake in association with health outcomes. (2) Funding agencies should only fund studies using the recommended method of multiple carefully collected complete 24-hour urine samples. (3) Journals and peer reviewers should only publish studies using recommended methods. Literature reviews that include studies using spot or short-duration timed urine samples must explicitly acknowledge that the method is not recommended and is associated with spurious associations. The authors note that major organizations including the British and Irish Hypertension Society, International Society of Nephrology, WHO Collaborating Centres, and the World Hypertension League have already recommended against using these methods. The statement aims to eliminate a major source of controversy about sodium reduction by stopping the publication and funding of methodologically flawed research.