Methods to measure salt intake at - PowerPoint Presentation

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Methods to measure salt intake at individual level: gold standard, proxy and calibration needsFrancesco P Cappuccio MD MSc DSc FRCP FFPH FBHS FAHAProfessor of Cardiovascular Medicine & EpidemiologyHead, WHO Collaborating CentreUniversity of Warwick, Coventry, UK

Disclosures: Technical Advisor to the World Health Organization, the Pan American Health Organization, Member of C.A.S.H., W.A.S.H., UK Health Forum and Trustee of the Student Heart Health TrustVice-President, British Hypertension Society – all unpaid.Slide2

How much sodium are we consuming? Slide3

Methods to estimate sodium intakeDuplicate dietsDietary surveysFood frequency7-day weighed recordsFood diary24-hour recallUrinary collectionSpot (casual)Overnight24-hour

Norfolk-EPIC Study (

Khaw

et al. 2004)

Men

WomenSlide4

BackgroundIn steady state, most of Na eaten in a day is excreted through urine in the following 24-h.24-h urinary Na excretion ‘gold standard’ for measuring sodium (salt) intake both in individuals and in populations.24-h collections often deemed inconvenient, hence alternative methods suggested (e.g. spot and timed urines).Their reliability and reproducibility often disappointing.However, in recent years a confusion has arisen as to what extent ‘proxy’ measures can be used to assess ‘salt’ intake.‘Population’ estimates (to monitor population policies) vs ‘Individual’ estimate (to use as exposure in research studies).Slide5

BackgroundGold standard: 24h urine collectionHigh participation burdenCompletenessNeed to explore alternativesCasual spotTimed (Day, Eve, Night)Estimation v ExtrapolationIndividual v GroupTheir reliability and reproducibility often disappointingSlide6

“Timed” urinesLess participant burden than 24 hour collectionsMore variable at individual level but may give good estimate of group meanDesirable alternative for monitoring program effects over time (validation necessary)Need baseline 24 hour urine assays to compare between populations or time pointsRole of urinary creatinineShould learn from monitoring program for iodisationCould be used for ‘effective’ monitoring of iodine (ideally in adult populations)Slide7

‘Spot’ urinesLess participant burden than 24 hour collectionsHighly variable at individual level but may give estimate of group meanLess desirable for monitoring program effects over timeHighly dependent on hydration, volume, residual bladder volumeCurrently used for monitoring iodine (mainly children and women of childbearing age)Extrapolated to 24h (validation studies published – interpretations vary - population specific ?)Slide8

Overnight collectionsLess participant burden than 24 hour collectionsMay give biased estimates of sodium excretion (greater % excretion overnight in hypertensive individuals…)Undesirable for monitoring program effects over timeSlide9
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Measurement of sodium intake

Sodium intake highly variable day to day

Misclassification of individual intake and increase in variance of group (mean unbiased)

Between

individuals

Within individuals

s

2

B

s

2

W

Reliability =

s

2

B

s

2

B

+

s

2

W

Liu K

et al. Hypertension

1979; 1: 529-36Slide11

The variability of 24-hour urinary sodium (…) was studied in a sample of 22 Neapolitan men with mild blood pressure elevation. On 5 days within a 1-month period, 24-hour urine specimens were collected by each subject. The estimated ratio of intraindividual-to-interindividual variance was 1.12 for urinary sodium, (…). Based on these values, five 24-hour urine collections are necessary to reduce to less than 10% the diminution of the correlation coefficient between urinary sodium and another related variable; this number is substantially lower than that found in previous studies in a North American population sample, but similar to the one reported for Chinese population samples (…). Siani A et al. Hypertension 1989; 13: 38-42How many 24h collections are needed to characterize an individual’s sodium excretion?Slide12

We performed 2 independent ultralong-term salt balance studies lasting 105 (4 men) and 205 (6 men) days in 10 menWe controlled dietary intake of all constituents for months at salt intakes of 12, 9, and 6 g/d and collected all urine. Urinary recovery of dietary salt was 92% of recorded intake.Even at fixed salt intake, 24-hour urine collection for sodium excretion (UNaV) showed infradian rhythmicity. Collecting seven 24-hour urines and sodium intake samples improved classification accuracy to 92%.Single 24-hour urine collections at intakes ranging from 6 to 12 g salt per day were not suitable to detect a 3-g difference in individual salt intake. Repeated measurements of 24-hour UNaV improve precision. This knowledge could be relevant to patient care and the conduct of intervention trials. Lerchl K et al. Hypertension. 2015

; 66: 850-7Slide13

Lerchl K et al. Hypertension 2015; 66: 850-7 Multiple collections reduce the variability and improve the predictive valueSlide14

DataStudy 1: Discovery sample915 British men & women aged 40-59 (297 W, 326 B, 292 SA)Study 2: Validation sample148 Italian White men aged 32-75Na, Cr in 24-h and timed spot urines

Reliability and Reproducibility

Tanaka

’

s method

†

Arithmetic extrapolation method

†: Tanaka T et al. J Hum Hyper,2002;16, 97-103.

Ji C et al.

Nutr

Metab

Cardiovasc

Dis

2014;

24: 140-7Slide15

Mean diff

95% CI

95% CI

Overestimation

Underestimation

Bland-Altman plot comparing

estimated

24h UNa

by Tanaka’s method and actually

measured

24h UNa

Ji

C et al.

Nutr

Metab

Cardiovasc

Dis 2014; 24: 140-7 Slide16

Bland-Altman plot

Tanaka

’

s method

Ji C et al.

Nutr

Metab

Cardiovasc

Dis

2014;

24: 140-7Slide17

The Prospective Urban Rural Epidemiological (PURE) StudySlide18

Peng Y et al. PLoS ONE 2016; DOI: 10.1371/journal.pone.0149655 To assess the validity of three methods (Kawasaki, INTERSALT, Tanaka) for estimating 24h urinary sodium excretion using spot urine samples against measured 24h urinary sodium excretion in a Chinese sample.Sub-study of the PURE study (120 participants 35-70 yrs; 4 excluded – final n=116)Morning fasting time urine and 24h urineMean bias for the Kawasaki method was the lowest among the three methods, that for the INTERSALT method was the highest. Bland-Altman plots indicated that all three methods underestimated 24-h urinary sodium excretion. Among the three methods, the Kawasaki method was least biased, but was still relatively inaccurate.

A more accurate method is needed to estimate the 24-h urinary sodium excretion from spot urine.The Prospective Urban Rural Epidemiological (PURE) Study:SUMMARYSlide19

Peng Y et al. PLoS ONE 2016; DOI: 10.1371/journal.pone.0149655 Slide20

The PURE StudyWe compared estimates of 24-h sodium excretion from a single morning fasting urine (MFU) using three different formulae in healthy individuals.We studied 1083 individuals aged 35-70 years from the general population in 11 countries. A 24-h urine and MFU specimen were obtained from each individual. A subset of 448 individuals repeated the measures after 30-90 days. The Kawasaki, Tanaka, and INTERSALT formulae were used to estimate urinary excretion from a MFU specimen.The intraclass correlation coefficient (ICC) between estimated and measured sodium excretion was higher with Kawasaki compared with INTERSALT and Tanaka formulae (P <0.001). The degree of bias (vs. the 24-h urine) for sodium was smaller with Kawasaki compared with INTERSALT and Tanaka formulae (P <0.001 and P = 0.02, respectively). In a diverse population, the Kawasaki formula is the most valid and least biased method of estimating 24-h sodium excretion from a single MFU and is suitable for population studies.

Mente

A et al. J

Hypertens

2014; 32: 1005-14

‘First void’ (overnight) urine sample

Kawasaki equation designed to assess ‘second’ void morning samples

Very high rate of incomplete collections (>50%)

Bias described higher at higher levels of 24h urinary sodium, likely due to incompleteness

Campbell

N. J

Hypertens 2014; 32: 2499-503 Slide21

Mean bias in predicted minus measured 24h urinary sodium excretion on the same day by prediction model and time of day*

Cogswell ME et al. Am J Clin Nutr

2013; 98: 1502-13

* Timed urine samples not independent of 24h sampleSlide22

Cogswell ME

et al. Am J Clin Nutr 2013; 98: 1502-13

Morning*

Afternoon*

Evening*

Overnight*

Bland-Altman plots of the relative bias between measured and predicted 24h urinary sodium excretion based on INTERSALT equation

* Timed urine samples not independent of 24h sampleSlide23

Spot timed urinary Na does not provide reliable and reproducible estimates of 24-h urinary Na excretion in an individual.Spot urines should not be used in cohort studies to estimate individuals’ exposures24-h urinary collection for the measurement of urinary Na excretion remains the preferred tool for assessing salt intake.Multiple collections are necessary to increase the prediction.ConclusionsSlide24

24-hour urine is the most accurate method for measuring population salt intake if carried out properly and measures are taken to ensure that the 24-hour urine collections are complete. Experts with experience in 24 hour urine collection e.g. endocrinologists, should be engaged to co-ordinate the surveys.If 24-hour urine collection is not feasible, there is some evidence that in a generally healthy adult (18-69) population, spot urine could approximate mean sodium intake and identify populations where salt intake is above the 5gram target. It is noted that this is a subject of ongoing research.To detect change over time in population salt intake, 24-hour urine is the most accurate method for repeat measurement but if not feasible, spot urine could approximate the mean sodium intake with some significant degree of underestimation of the change over time to take into consideration 24-hour urine is the most accurate method of assessing individual sodium intake and single spot or short duration timed urine samples are inappropriate to use for this purpose

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