Publications
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Alderman M, 1997, Intersalt data. Data linking sodium intake to subsequent morbid and fatal outcomes must be studied., BMJ, Vol: 315, Pages: 484-485, ISSN: 0959-8138
Dyer A, Elliott P, Chee D, et al., 1997, Urinary biochemical markers of dietary intake in the INTERSALT study., Pages: 1246S-1253S, ISSN: 0002-9165
The INTERSALT Study, an international, collaborative, cross-sectional investigation of the relation between blood pressure and dietary and other factors, used quality-controlled, standardized procedures and assessment of multiple possible confounding factors to study 10,079 men and women in 52 population-based samples in 32 countries. In this study 24-h urinary excretion data were used as biochemical markers of intakes of sodium, potassium, and protein, with repeat examinations done in a randomly selected 8% of participants to asses reliability and correct for regression-dilution bias. INTERSALT showed that high salt intake, low potassium intake, excess alcohol consumption, and energy imbalance resulting in overweight are critically involved in the origins of the high blood pressure prevalent among a majority of adult populations. The findings also show that obtaining accurate estimates of associations between dietary intake and blood pressure requires large population-based samples, high-quality dietary information, control for multiple confounding variables, and modern multivariate methods of data analyses, including correction of observed associations for within-person variation in intake.
Pryer JA, Vrijheid M, Nichols R, et al., 1997, Who are the 'low energy reporters' in the dietary and nutritional survey of British adults?, Int J Epidemiol, Vol: 26, Pages: 146-154, ISSN: 0300-5771
BACKGROUND: Underreportin in dietary surveys is a potential source of bias in studies of diet and disease. The aim of this study was to identify characteristics of men and women participants in the Dietary and Nutritional Survey of British Adults (DNSBA) who stated that they were neither slimming nor ill, and who reported an average energy intake over a 7-day period below 1.2 times estimated basal metabolic rate (BMR), termed here 'low energy reporters' (LER). METHODS: In all, 2197 men and women aged 16-64 years participated in the DNSBA. Dietary intake was assessed using the 7-day weighed intake method. Their BMR was estimated using predictive equations based upon age, sex and body weight. RESULTS: Compared with non-LER, LER had higher mean ratios of urinary urea nitrogen to dietary nitrogen and urinary potassium to dietary potassium, indicating that, as a group, LER were underreporting at least for protein and potassium intakes. Overall LER were overrepresented among the manual social classes, smokers, and self-reported non-alcohol drinkers, and were on average heavier than non-LER. There was indication of differential reporting of foods and differences in macronutrient and micronutrient densities between LER and non-LER. CONCLUSION: These results suggest that LER may be overrepresented within specific population subgroups and that underreporting bias may not be food and nutrient neutral. This has implications for the design and interpretation of studies of diet and disease.
Le Fanu J, Alderman M, Macnair A, et al., 1997, Intersalt data (multiple letters) [1], British Medical Journal, Vol: 315, Pages: 484-488, ISSN: 0959-8146
Martuzzi M, Elliott P, 1996, Empirical Bayes estimation of small area prevalence of non-rare conditions., Stat Med, Vol: 15, Pages: 1867-1873, ISSN: 0277-6715
Geographical studies are becoming increasingly common in epidemiology. The problems of small area investigations are well known, and several methods are available for the estimation and mapping of disease risk across small areas, with the emphasis mainly on applications concerning rare disease incidence or mortality. An empirical Bayes method is proposed for small area estimation of the prevalence of non-rare conditions, whose variability is binomial and cannot be approximated by a Poisson model. It is the direct equivalent of a semi-parametric non-iterative moment estimation method proposed in the Poisson case. As an example, the geographical distribution of the prevalence of respiratory symptoms in schoolchildren across 71 small areas in Huddersfield, Northern England is studied. Whereas random variability causes the crude area-specific prevalences to be unstable, the posterior estimates, corrected towards overall or local means, are capable of highlighting genuine extra-binomial variability. The method is very simple and can readily be applied to the study of a number of common conditions.
Joossens JV, Hill MJ, Elliott P, et al., 1996, Dietary salt, nitrate and stomach cancer mortality in 24 countries. European Cancer Prevention (ECP) and the INTERSALT Cooperative Research Group., Int J Epidemiol, Vol: 25, Pages: 494-504, ISSN: 0300-5771
BACKGROUND: High salt and nitrate intake are considered as risk factors for stomach cancer, but little is known about possible interactions. This ecological study examines the respective importance of both factors for stomach cancer mortality at the population level using data obtained under standardized conditions and with biochemical analyses performed in the same laboratories. METHODS: Randomly selected 24-hour urine samples from 39 populations, sampled from 24 countries (N = 5756 people for sodium, 3303 for nitrate) were obtained from the INTERSALT study. Median sodium and nitrate levels were age- and sex-standardized between ages 20-49 years and averaged per country. Ecological correlation-regression analyses were done in relation to national stomach cancer mortality rates. RESULTS: The Pearson correlation of stomach cancer mortality with sodium for the 24 countries was: 0.70 in men and 0.74 in women (both P < 0.001) and with nitrate: 0.63 (P = 0.001) in men and (P < 0.005) in women. In multiple regression of stomach cancer mortality, using sodium and nitrate as independent variables the adjusted R2 was 0.61 in men and 0.54 in women (both P < 0.001). Addition of the interaction term (sodium x nitrate) to the previous model increased the adjusted R2 to 0.77 in men, and to 0.63 in women. The analysis of this model showed that the importance of nitrate as risk factor for stomach cancer mortality increased markedly with higher sodium levels. However, the relationship of stomach cancer mortality with sodium was always stronger than with nitrate. CONCLUSIONS: Salt intake, measured as 24-hour urine sodium excretion, is likely the rate-limiting factor of stomach cancer mortality at the population level.
Hill MJ, Elliott P, Joossens JV, et al., 1996, Twenty-four hour urinary nitrate excretion in 48 populations from 30 countries: an ECP-INTERSALT collaborative study., Int J Epidemiol, Vol: 25, Pages: 505-512, ISSN: 0300-5771
BACKGROUND: There is considerable interest in the possible role of nitrate in gastric carcinogenesis, but little information on nitrate intake around the world. This is the first study to give comprehensive standardised data on nitrate excretion as a marker of intake, using 48 worldwide population samples. METHODS: Urinary nitrate excretion has been shown to be a valid measure of nitrate intake in people under 50. This report presents data on 24-hour urinary nitrate excretion from urine collections obtained in the INTERSALT study, based on random samples of men and women aged 20-49 from each of 48 population samples in 30 countries. RESULTS: There was large variation in urinary nitrate excretion both within and between samples; within-sample (individual) distributions tended to be skewed towards higher values. Median values of the samples ranged from 0.42 mmol/day (Labrador, Canada) to 3.52 (Beijing, People's Republic of China) in men and 0.44 mmol/day (Colombia) to 3.44 (Beijing) in women. Overall, median values were higher in men than women by 11% on average (higher in men in 37 of 48 population samples). Comparison by geographical region of median values for men and women combined showed relatively low values in the samples in North America and Northern Europe (range 0.46-0.88 mmol/day), slightly higher values in Western Europe and Africa (0.68-1.11), and intermediate to high values in Southern Europe, Eastern and Central Europe and India (0.86-2.47). The highest median values were found in the Far Eastern samples (up to 3.48). Median values in the Central and South American samples ranged from 0.48 mmol/day (Colombia) to 1.37 (Xingu Indians of Brazil, and Argentina). CONCLUSIONS: For the first time, these data give standardized information on urinary nitrate excretion from different geographical regions of the world, and provide a basis for the further exploration of the role of nitrate in the aetiology of disease in human populations.
Stamler J, Elliott P, Dyer AR, et al., 1996, Commentary: Sodium and blood pressure in the Intersalt study and other studies—in reply to the Salt Institute, BMJ, Vol: 312, Pages: 1285-1287, ISSN: 0959-8138
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Allender PS, Cutler JA, Follmann D, et al., 1996, Dietary calcium and blood pressure: a meta-analysis of randomized clinical trials., Ann Intern Med, Vol: 124, Pages: 825-831, ISSN: 0003-4819
PURPOSE: To assess the effect of dietary calcium supplementation on blood pressure. DATA SOURCES: Published reports of trials studying the effect of dietary calcium supplementation on blood pressure were identified by a search of previous reviews, a MEDLINE search, a manual review of journal articles, and a review of abstracts from scientific meetings. STUDY SELECTION: Randomized clinical trials in which dietary calcium intake varied by intervention group were selected. Multifactorial trials were not included. DATA SYNTHESIS: Data from 28 active treatment arms or strata from 22 randomized clinical trials were pooled using a weighted average method, with weights proportional to the inverse of the variance of the treatment effect. The total sample comprised 1231 persons. Because trials of both normotensive and hypertensive persons were included, subgroup analyses could be done. Pooled estimates of the effect of calcium supplementation on blood pressure were -0.18 mm Hg for diastolic blood pressure (95% CI, -0.75 to 0.40 mm Hg) and -0.89 mm Hg for systolic blood pressure (CI, -1.74 to -0.05 mm Hg). Pooled estimates for systolic blood pressure were -0.53 mm Hg (CI, -1.56 to 0.49 mm Hg) for trials of normotensive persons and -1.68 mm Hg (CI, -3.18 to -0.18 mm Hg) for trials of hypertensive persons. Diastolic blood pressure was not significantly affected in either subgroup. CONCLUSION: The pooled estimate shows a statistically significant decrease of systolic blood pressure with calcium supplementation, both for hypertensive persons and for the overall sample. However, the effect is too small to support the use of calcium supplementation for preventing or treating hypertension.
Livingstone AE, Shaddick G, Grundy C, et al., 1996, Do people living near inner city main roads have more asthma needing treatment? Case control study., BMJ, Vol: 312, Pages: 676-677, ISSN: 0959-8138
Dyer AR, Stamler R, Elliott P, et al., 1995, Dietary salt and blood pressure., Nat Med, Vol: 1, Pages: 994-996, ISSN: 1078-8956
Follmann D, Elliott P, Suh I, et al., 1992, Variance imputation for overviews of clinical trials with continuous response., J Clin Epidemiol, Vol: 45, Pages: 769-773, ISSN: 0895-4356
Overviews of clinical trials are an efficient and important means of summarizing information about a particular scientific area. When the outcome is a continuous variable, both treatment effect and variance estimates are required to construct a confidence interval for the overall treatment effect. Often, only partial information about the variance is provided in the publication of the clinical trial. This paper provides heuristic suggestions for variance imputation based on partial variance information. Both pretest-posttest (parallel groups) and crossover designs are considered. A key idea is to use separate sources of incomplete information to help choose a better variance estimate. The imputation suggestions are illustrated with a data set.
Elliott P, 1991, Observational studies of salt and blood pressure., Pages: I3-I8, ISSN: 0194-911X
The observational data relating salt and blood pressure (excluding INTERSALT) are reviewed. Important methodological difficulties and biases are inherent to both across- and within-population studies and confuse their interpretation. Across-population studies are positive but rely on data drawn from the international literature based on a variety of unstandardized field methods; they are prone to unmeasured (ecological) confounding. Within-population studies generally lack statistical power and are subject to major regression-dilution bias (because of considerable day-to-day variation in sodium intake), which could conceal true correlations between sodium and blood pressure. Nevertheless, an overview of reported studies that used 24-hour urine excretion to quantify intake shows positive and highly significant correlations between sodium and blood pressure for both men and women and for systolic and diastolic blood pressures. These results are consistent with the INTERSALT findings and those from trials of sodium restriction.
Stamler J, Rose G, Elliott P, et al., 1991, Findings of the International Cooperative INTERSALT Study., Hypertension, Vol: 17, Pages: I9-15, ISSN: 0194-911X
INTERSALT, an international cooperative study on electrolytes and other factors related to blood pressure, found, in within-population analyses involving 10,079 persons, a significant positive association between 24-hour urinary sodium excretion and systolic blood pressure and between the sodium/potassium ratio and systolic blood pressure. These significant findings were derived from analyses for individuals from all 52 centers and from the 48 centers remaining when persons from four low sodium centers were excluded. Potassium excretion of individuals was significantly and independently related inversely to their systolic blood pressure. For men and women, both separate and combined, the relation between sodium and systolic blood pressure was stronger for older than younger adults, perhaps reflecting the result of longer exposure with age or diminished capacity to handle a sodium load. Relations between electrolyte excretion and diastolic blood pressure in individuals were weaker than for systolic blood pressure. Body mass index and heavy alcohol consumption of individuals were strongly and independently related to blood pressure. In cross-population analyses with n = 52 or n = 48, sample median sodium excretion was significantly and independently related to the slope of systolic blood pressure and diastolic blood pressure with age. Other ecological analyses yielded inconsistent results. Four isolated populations showed low sodium excretion, low sodium/potassium excretion, low body mass index, and low alcohol consumption; sample median blood pressures were low, there was little or no upward slope of blood pressure with age, and high blood pressure was rare or nonexistent.
Elliott P, 1990, Small area health statistics in Europe, Information Services and Use, Vol: 10, Pages: 39-45, ISSN: 0167-5265
The use of routine health statistics in monitoring the health of populations in small areas is an important and exciting advance in environmental epidemiology. Requirements for a national system are discussed and illustrated with reference to the new Small Area Health Statistics Unit at the London School of Hygiene and Tropical Medicine. It is hoped that collaboration with groups in other countries holding similar data might be possible to extend and improve the methodology and also the power of small area based analyses. © 1990 Elsevier Science Publishers B.V.
Stamler J, Rose G, Stamler R, et al., 1989, INTERSALT study findings. Public health and medical care implications., Hypertension, Vol: 14, Pages: 570-577, ISSN: 0194-911X
INTERSALT found a significant association between 24-hour urine sodium excretion and systolic blood pressure in individuals. There was also a significant association between sodium and slope (increase) of blood pressure with age across population samples. The weight of evidence from animal-experimental, clinical, intervention, and epidemiological data favors a causal relation. INTERSALT data from 52 centers in 32 countries permit an estimate of effect on average population blood pressure of lower sodium intake. Based on the sodium-blood pressure association in individuals, it was estimated that a habitual population sodium intake that was lower by 100 mmol/day (e.g., 70 vs. 170 mmol/day) would correspond to an average population systolic pressure that was lower by at least 2.2 mm Hg. This size difference in systolic blood pressure in major US and UK population studies is associated with 4% lower risk of coronary death and 6% lower risk of stroke death in middle age. If habitual diet is both lower in sodium and higher in potassium with lower alcohol intake and less obesity, INTERSALT data estimate average population systolic pressure would be lower by 5 mm Hg. This was calculated to correspond to a 9% lower risk of coronary death and a 14% lower risk of stroke death. INTERSALT cross-population data also suggest that, with a 100 mmol/day lower sodium intake over the life span, the average increase in population systolic pressure from age 25 to 55 years would be less by 9 mm Hg, corresponding at age 55 to a 16% lower risk of subsequent coronary death and 23% lower risk of stroke death.(ABSTRACT TRUNCATED AT 250 WORDS)
CARVALHO JJM, BARUZZI RG, HOWARD PF, et al., 1989, BLOOD-PRESSURE IN 4 REMOTE POPULATIONS IN THE INTERSALT STUDY, HYPERTENSION, Vol: 14, Pages: 238-246, ISSN: 0194-911X
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- Citations: 195
Marmot MG, Elliott P, 1989, Public health measures for blood pressure control in the whole community., Clin Exp Hypertens A, Vol: 11, Pages: 1171-1186, ISSN: 0730-0077
One approach to the prevention of blood pressure-associated cardiovascular disease is to find increased numbers of "hypertensives" and bring them under treatment. A complementary approach is to attempt to change the blood pressure distribution of the whole population. It can be calculated that, if the association between blood pressure level and mortality were reversible, a reduction of diastolic blood pressure of 5 mmHg in the population mean would be associated with a substantial reduction in cardiovascular mortality. The assumption of reversibility of risk of coronary heart disease may be more reasonable in the long than in the short term. The evidence from INTERSALT and other studies suggests that readily achievable changes in sodium and potassium intake, in body mass index and in alcohol intake, could lead to average blood pressure change across a whole population of 5 mmHg. A major task for public health is the implementation of such life-style changes among different social class and ethnic groups.
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