The association between urinary sodium excretion and blood pressure in children

Estimation of Salt Intake in Normotensive and Hypertensive Children: The Role of Body Weight

OBJECTIVE

The connection between increased dietary salt intake and arterial hypertension has been recognized for a long time, even in children. This study aimed to investigate salt consumption in normotensive and hypertensive children and evaluate their dietary habits.

MATERIALS AND METHODS

A total of fifty participants were included in this cross-sectional study: twenty-five normotensive children and 25 children of both sexes with essential arterial hypertension from 12-17 years old. Subjects' body mass index, waist-to-hip ratio, body composition and arterial blood pressure were measured, and their daily salt intake was calculated from 24-h urine samples. Using the food frequency questionnaire (FFQ), the data on the average daily total energy and food intakes were collected and analyzed using a suitable program.

RESULTS

Estimated daily salt intake was significantly higher in hypertensive compared to normotensive children, and this is positively associated with blood pressure and body mass index (BMI). Hypertensive children had significantly higher BMIs, which also positively correlated with blood pressure. Consistently, resting metabolic rate (kcal) is higher in hypertensive children compared to normotensive, and this is also associated with blood pressure. Reported energy intake is also enlarged in hypertensive compared to normotensive children and for both groups, levels are significantly higher than the recommended values.

CONCLUSIONS

Our study results confirm the relationship between daily salt consumption, blood pressure and body weight. Sodium consumption related to blood pressure and body weight among children. Cardiovascular disease prevention should start in early childhood by reducing salt intake and preventing overweight/obesity since these are two of the most important modifiable risk factors for hypertension.

Assessing the Association of Sodium, Potassium Intake and Sodium/Potassium Ratio on Blood Pressure and Central Adiposity Measurements amongst Ellisras Undernourished, Rural Children Aged 5–13 Years: South Africa

Background: Numerous studies have shown how diet, such as sodium (Na) and potassium (K) intake, is an important risk factor for non-communicable diseases (NCDs). This study aimed to assess the relationship between sodium intake, potassium intake; and sodium/potassium ratio with blood pressure (BP) and abdominal obesity amongst Ellisras rural children. Method: In this cross-sectional study, data on dietary intake of sodium and potassium were collected using a 24-h recall questionnaire from a total of 765 participants, aged 5–13 years. Blood pressure and anthropometric measurements were also collected. Generalised linear models and Pearson correlation were conducted to assess the association of sodium intake, potassium intake; and their ratio with BP, waist circumference (WC), and waist-to-height ratio (WHtR). Results: In both age groups, less than 14.9% of males and 19.8% of females consumed above the recommended adequate intake (AI) of sodium. In addition, both age groups had more than 90% of males and females who consumed below the recommended AI of potassium. Moreover, the sodium/potassium ratio was above the WHO recommended level in more than 30% of males and females. The study found a significant, weak positive correlation of sodium intake with systolic BP (SBP), diastolic BP (DBP), and with WHtR. A significant, weak positive correlation was also found between sodium/potassium ratio and WHtR. In addition, a significant association was found between potassium intake and systolic BP. Conclusion: Although our study found a notable low average intake of sodium and potassium as compared to the recommended values. There was positive correlation found between sodium intake and BP. Furthermore, a positive correlation of sodium intake and sodium/potassium ratio with WHtR was also found.

Trends in Sodium Intake in Children and Adolescents in the US and the Impact of US Department of Agriculture Guidelines: NHANES 2003-2016

OBJECTIVE

To examine trends in sodium intake and the impact of nutritional guidelines in the US pediatric population.

STUDY DESIGN

Sodium intake data collected between 2003 and 2016 in the US National Health and Nutrition Examination Surveys (NHANES) were analyzed. Trends in intake for individuals aged 4-17 years and subgroups based on age, sex, and race and ethnicity were examined. Adherence to US Department of Agriculture guidelines was assessed.

RESULTS

A total of 16 013 individuals (50.6% male) were included in the analysis. The median sodium intake was 2840 mg/day (95% CI, 2805-2875 mg/day), decreasing from 2912 mg/day (95% CI 2848-2961 mg/day) in 2003-2004 to 2787 mg/day (95% CI, 2677-2867 mg/day) in 2015-2016 (P = .005). Intake increased with age (2507 mg/day for individuals aged 4-8, 2934 mg/day for those aged 9-13 years, and 3124 mg/day for those aged 14-17 years; P < .001) and was greater in males than in females (3053 mg/day vs 2624 mg/day; P < .001). Caucasians, Hispanics, and African Americans consumed 2860, 2733, and 2880 mg/day, respectively (P < .001). Population adherence to US Department of Agriculture recommendations was 25.0% in 2003-2010 and 25.5% in 2011-2016 (P = .677). No age, sex, or racial/ethnicity subgroup had an adherence rate >30% after implementation of pediatric guidelines in 2010.

CONCLUSIONS

Sodium intake remains elevated in all pediatric population segments, and guideline adherence is poor. A greater effort to reduce sodium consumption is needed to mitigate future cardiovascular disease risk.

Social support, social network and salt-reduction behaviours in children: a substudy of the School-EduSalt trial

OBJECTIVES

Healthy behaviour changes, such as reducing salt intake, are important to prevent lifestyle-related diseases. Social environment is a major challenge to achieve such behaviours, but the explicit mechanisms remain largely unknown. We investigated whether social networks of children were associated with their behaviours to reduce salt intake.

DESIGN

An ancillary study of a school-based cluster randomised controlled trial to reduce salt intake in children and their families (School-EduSalt), in which salt intake of children was significantly reduced by 25%.

SETTING

14 primary schools in urban Changzhi, northern China.

PARTICIPANTS

603 children aged 10-12 years in the intervention arm.

PRIMARY AND SECONDARY OUTCOME MEASURES

We developed a score assessing salt-reduction behaviours (SRB score) of children based on self-administered questionnaires. The SRB score was validated by the changes in salt intake measured by 24-hour urine collection in a random sample of 135 children. A 1-unit increase in SRB score was associated with a 0.31 g/day greater reduction in salt intake during the trial (95% CI 0.06 to 0.57, p=0.016).

RESULTS

Children from families with more family members not supporting salt reduction had significantly lower SRB scores (p<0.0001). Children from a class with a smaller size and from a class with more friendship connections, as well as children having more friends within the class all showed higher SRB scores (all p<0.05). Children whose school teachers attended the intervention programme more frequently also had higher SRB scores (p=0.043).

CONCLUSION

Social networks were associated with the behaviours to reduce salt intake in children. Future salt-reduction programmes may benefit from strategies that actively engage families and teachers, and strategies that enhance interconnectivity among peers.

TRIAL REGISTRATION NUMBER

NCT01821144; post-results.

Sodium intake and blood pressure in children and adolescents: a systematic review and meta-analysis of experimental and observational studies

Background

High sodium intake is a cause of elevated blood pressure in adults. In children and adolescents, less evidence is available and findings are equivocal. We systematically reviewed the evidence from experimental and observational studies on the association between sodium intake and blood pressure in children and adolescents.

Methods

A systematic search of the Medline, Embase, CINAHL and CENTRAL databases up to March 2017 was conducted and supplemented by a manual search of bibliographies and unpublished studies. Experimental and observational studies involving children or adolescents between 0 and 18 years of age were included. Random-effects meta-analyses were performed by pooling data across all studies, separately for experimental and observational studies, and restricting to studies with sodium intake and blood pressure measurement methods of high quality. Subgroup meta-analyses, sensitivity analyses and meta-regressions were conducted to investigate sources of heterogeneity and confounding. The dose-response relationship was also investigated.

Results

Of the 6572 publications identified, 85 studies (14 experimental; 71 observational, including 60 cross-sectional, 6 cohort and 5 case-control studies) with 58 531 participants were included. In experimental studies, sodium reduction interventions decreased systolic blood pressure by 0.6 mm Hg [95% confidence interval (CI): 0.5, 0.8] and diastolic blood pressure by 1.2 mm Hg (95% CI: 0.4, 1.9). The meta-analysis of 18 experimental and observational studies (including 3406 participants) with sodium intake and blood pressure measurement methods of high quality showed that, for every additional gram of sodium intake per day, systolic blood pressure increased by 0.8 mm Hg (95% CI: 0.4, 1.3) and diastolic blood pressure by 0.7 mm Hg (95% CI: 0.0, 1.4). The association was stronger among children with overweight and with low potassium intake. A quasi-linear relationship was found between sodium intake and blood pressure.

Conclusions

Sodium intake is positively associated with blood pressure in children and adolescents, with consistent findings in experimental and observational studies. Since blood pressure tracks across the life course, our findings support the reduction of sodium intake during childhood and adolescence to lower blood pressure and prevent the development of hypertension.

Urine Spot Samples Can Be Used to Estimate 24-Hour Urinary Sodium Excretion in Children

Background

The gold standard to assess salt intake is 24-h urine collections. Use of a urine spot sample can be a simpler alternative, especially when the goal is to assess sodium intake at the population level. Several equations to estimate 24-h urinary sodium excretion from urine spot samples have been tested in adults, but not in children.

Objective

The objective of this study was to assess the ability of several equations and urine spot samples to estimate 24-h urinary sodium excretion in children.

Methods

A cross-sectional study of children between 6 and 16 y of age was conducted. Each child collected one 24-h urine sample and 3 timed urine spot samples, i.e., evening (last void before going to bed), overnight (first void in the morning), and morning (second void in the morning). Eight equations (i.e., Kawasaki, Tanaka, Remer, Mage, Brown with and without potassium, Toft, and Meng) were used to estimate 24-h urinary sodium excretion. The estimates from the different spot samples and equations were compared with the measured excretion through the use of several statistics.

Results

Among the 101 children recruited, 86 had a complete 24-h urine collection and were included in the analysis (mean age: 10.5 y). The mean measured 24-h urinary sodium excretion was 2.5 g (range: 0.8-6.4 g). The different spot samples and equations provided highly heterogeneous estimates of the 24-h urinary sodium excretion. The overnight spot samples with the Tanaka and Brown equations provided the most accurate estimates (mean bias: -0.20 to -0.12 g; correlation: 0.48-0.53; precision: 69.7-76.5%; sensitivity: 76.9-81.6%; specificity: 66.7%; and misclassification: 23.0-27.7%). The other equations, irrespective of the timing of the spot, provided less accurate estimates.

Conclusions

Urine spot samples, with selected equations, might provide accurate estimates of the 24-h sodium excretion in children at a population level. At an individual level, they could be used to identify children with high sodium excretion. This study was registered at clinicaltrials.gov as NCT02900261.

Estimation of salt intake and excretion in children in one region of Switzerland: a cross-sectional study

PURPOSE

Salt intake among children in Switzerland is unknown. The objectives of this study were to determine salt excretion and to identify the main dietary sources of salt intake among children in one region of Switzerland.

METHODS

We conducted a cross-sectional study using a convenient sample of children 6-16 years of age in Valais, Switzerland, between 2016 and 2018. All children visiting several regional health care providers and without any clinical condition that could affect sodium intake or excretion were eligible. Each child completed a 24-h urine collection to assess salt excretion and two dietary questionnaires to assess dietary sources of salt intake. Weight and height were measured.

RESULTS

Data were available on 94 children (55 boys and 39 girls; mean age 10.5 years; age range 6-16 years). The mean 24-h salt urinary excretion was 5.9 g [SD 2.8; range 0.8-16.0; 95% confidence interval (CI) 5.3-6.5]. Two-thirds (62%) of the children had salt excretions above recommendations of maximum intake (i.e., ≥ 2 g per day for children up to 6 years of age and ≥ 5 g per day for children 7-16 years of age). The salt excretion tended to be higher during the week-end (6.0 g, 95% CI 5.4-6.6) than during the week (5.4 g, 95% CI 4.3-6.7). The main sources of salt intake were pastas, potatoes, and rice (23% of total salt intake), pastries (16%), bread (16%), and cured meats (10%). One child out of three (34%) added salt to their plate at the table.

CONCLUSIONS

Salt intake in children in one region of Switzerland was high. Our findings suggest that salt intake in children could be reduced by lowering salt content in commonly eaten foods.

TRIAL REGISTRATION NUMBER

NCT02900261.

Independent association of resting energy expenditure with blood pressure: confirmation in populations of the African diaspora

BACKGROUND

Obesity is a major risk factor for hypertension, however, the physiologic mechanisms linking increased adiposity to elevations in blood pressure are not well described. An increase in resting energy expenditure (REE) is an obligatory consequence of obesity. Previous survey research has demonstrated that REE is an independent predictor of blood pressure, and eliminates the co-linear association of body mass index. This observation has received little attention and there have been no attempts to provide a causal explanation.

METHODS

At baseline in an international comparative study on obesity, 289 participants aged 25-44 were recruited from communities in the US, the Seychelles, Ghana and South Africa and had REE measured with indirect calorimetry. All participants were thought to be free of major illness.

RESULTS

In multivariate regression models, both systolic and diastolic blood pressure were positively associated with REE (p < 0.01), while body mass index and fat mass were negatively correlated with systolic blood pressure (p < 0.01, and p < 0.05 respectively), but not diastolic blood pressure.

CONCLUSIONS

These data confirm previous reports and suggest that a common physiologic abnormality links REE and blood pressure. Elevated catecholamines, a putative metabolic characteristic of obesity, is a possible candidate to explain this association. The direct role of excess adipose tissue is open to question.

Sodium intake and blood pressure in children and adolescents: protocol for a systematic review and meta-analysis

INTRODUCTION

Hypertension is a major risk factor for cardiovascular diseases. In adults, high sodium intake is associated with elevated blood pressure. In children, experimental studies have shown that reducing sodium intake can reduce blood pressure. However, their external validity is limited, notably because the sodium reduction was substantial and not applicable in a real-life setting. Observational studies, on the other hand, allow assess the association between blood pressure and sodium intake across usual levels of consumption. There is also evidence that the association differs between subgroups of children according to age and body weight. Our objective is to conduct a systematic review and meta-analysis of experimental and observational studies on the association between sodium intake and blood pressure in children and adolescents and to assess whether the association differs according to age and body weight.

METHODS AND ANALYSIS

A systematic search of the MEDLINE, EMBASE, CINAHL and CENTRAL databases will be conducted and supplemented by a manual search of bibliographies and unpublished studies. Experimental and observational studies involving children or adolescents between 0 and 18 years of age will be included. The exposure will be dietary sodium intake, estimated using different methods including urinary sodium excretion. The outcomes will be systolic and diastolic blood pressure, elevated blood pressure and hypertension. If appropriate, meta-analyses will be performed by pooling data across all studies together and separately for experimental and observational studies. Subgroup meta-analyses by age and body weight will be also conducted. Moreover, separate meta-analyses for different sodium intake levels will be conducted to investigate the dose-response relationship.

ETHICS AND DISSEMINATION

This systematic review and meta-analysis will be published in a peer-reviewed journal. A report will be prepared for national authorities and other stakeholders in the domains of nutrition, public health, and child health in Switzerland.

TRIAL REGISTRATION NUMBER

CRD42016038245.

Dietary sources and sodium intake in a sample of Australian preschool children

OBJECTIVES

To assess dietary sodium intake and the food sources of sodium in a sample of Australian preschool children.

DESIGN

Cross-sectional.

SETTING

Mothers were followed up when children were approximately 3.5 years of age after participating in a cluster randomised controlled trial: the Melbourne Infant Feeding Activity and Nutrition Trial Program.

PARTICIPANTS

251 Australian children aged 3.5 ± 0.19 (SD) years.

PRIMARY AND SECONDARY OUTCOME MEASURES

The average daily sodium intake was determined using three unscheduled 24 h dietary recalls. The contributions of food groups, core, discretionary and processed foods to daily sodium intake were assessed.

RESULTS

The average sodium intake was 1508 ± 495 (SD) mg/day, (salt equivalent 3.9 ± 1.3 (SD) g/day) and 87% of children exceeded the Australian Upper Level of Intake (UL) for sodium of 1000 mg/day (salt equivalent 2.6 g/day). Main food sources of sodium were cereal/cereal products (25%), milk products (19%), meat, poultry/game (17%) and cereal-based products (15%). Core foods contributed 65%, and discretionary foods 35% of total daily sodium intake, and within the total diet, minimally processed, processed, processed culinary ingredient and ultraprocessed foods contributed 16%, 35%, 1% and 48% of sodium, respectively.

CONCLUSIONS

Within this sample, most children exceeded the recommended UL for sodium. Core and ultraprocessed foods were key sources of sodium which suggests that reductions in the sodium content of these foods are required to reduce sodium intake in young children. These data also provide further support for public health campaigns that seek to reduce consumption of energy-dense, nutrient-poor foods.

Cross-Sectional Study of 24-Hour Urinary Electrolyte Excretion and Associated Health Outcomes in a Convenience Sample of Australian Primary Schoolchildren: The Salt and Other Nutrients in Children (SONIC) Study Protocol

BACKGROUND

Dietary sodium and potassium are involved in the pathogenesis of cardiovascular disease. Data exploring the cardiovascular outcomes associated with these electrolytes within Australian children is sparse. Furthermore, an objective measure of sodium and potassium intake within this group is lacking.

OBJECTIVE

The primary aim of the Salt and Other Nutrient Intakes in Children ("SONIC") study was to measure sodium and potassium intakes in a sample of primary schoolchildren located in Victoria, Australia, using 24-hour urine collections. Secondary aims were to identify the dietary sources of sodium and potassium, examine the association between these electrolytes and cardiovascular risk factors, and assess children's taste preferences and saltiness perception of manufactured foods.

METHODS

A cross-sectional study was conducted in a convenience sample of schoolchildren attending primary schools in Victoria, Australia. Participants completed one 24-hour urine collection, which was analyzed for sodium, potassium, and creatinine. Completeness of collections was assessed using collection time, total volume, and urinary creatinine. One 24-hour dietary recall was completed to assess dietary intake. Other data collected included blood pressure, body weight, height, waist and hip circumference. Children were also presented with high and low sodium variants of food products and asked to discriminate salt level and choose their preferred variant. Parents provided demographic information and information on use of discretionary salt. Descriptive statistics will be used to describe sodium and potassium intakes. Linear and logistic regression models with clustered robust standard errors will be used to assess the association between electrolyte intake and health outcomes (blood pressure and body mass index/BMI z-score and waist circumference) and to assess differences in taste preference and discrimination between high and low sodium foods, and correlations between preference, sodium intake, and covariates.

RESULTS

A total of 780 children across 43 schools participated. The results from this study are expected at the end of 2015.

CONCLUSIONS

This study will provide the first objective measure of sodium and potassium intake in Australian schoolchildren and improve our understanding of the relationship of these electrolytes to cardiovascular risk factors. Furthermore, this study will provide insight into child taste preferences and explore related factors. Given the cardiovascular implications of consuming too much sodium and too little potassium, monitoring of these nutrients during childhood is an important public health initiative.

Associations among blood pressure, salt consumption and body weight status of students from south-western Ontario

OBJECTIVE

The purpose was to examine the associations among body weight status, blood pressure and daily Na intake among grade 7 students from south-western Ontario, Canada.

DESIGN

Cross-sectional. Data were collected using the Food Behaviour Questionnaire, including a 24 h diet recall. Measured height and weight were used to determine BMI. Blood pressure was taken manually using mercury sphygmomanometers.

SETTING

Twenty-six schools in south-western Ontario, Canada.

SUBJECTS

Grade 7 students (n 1068).

RESULTS

Body weight status indicated 1 % were underweight, 56 % normal weight, 23 % overweight and 20 % were obese. Mean systolic blood pressure (SBP) and diastolic blood pressure (DBP) were 108·3 (sd 10·3) mmHg and 66·0 (sd 7·5) mmHg, respectively, and mean Na intake was 2799 (sd 1539) mg/d. Bivariate analyses suggested that SBP (P < 0·001) and DBP (P < 0·001) were significantly different by body weight status, yet no associations were observed for Na. Adjusted for gender, ethnicity and under-reporting, participants were more likely to be overweight/obese if they had higher SBP (v. lower: OR = 1·06, 95 % CI 1·05, 1·08, P < 0·001), higher DBP (v. lower: OR = 1·02, 95 % CI 1·00, 1·04, P = 0·043) and higher intakes of Na (3rd v. 1st quartile: OR = 1·72, 95 % CI 1·14, 2·59, P = 0·009; 4th v. 1st quartile: OR = 2·88, 95 % CI, 1·76, 4·73, P < 0·001).

CONCLUSIONS

High intakes of Na, coupled with high SBP and DBP, were associated with overweight and obesity status among the grade 7 sample from south-western Ontario, Canada.

Salt, fruit and vegetable consumption and blood pressure development: a longitudinal investigation in healthy children

Low salt intake and high fruit and vegetable intake (FVI) have been shown to reduce blood pressure (BP) in adults. Longitudinal data on the independent effect of both FVI and salt intake on BP in healthy normotensive children are not available yet. In the present study, we aimed to characterise the concomitant influence of salt intake and FVI on BP development throughout childhood and adolescence. We examined 435 healthy subjects, for whom at least three repeated measurements of BP had been taken and who had provided 24 h urine samples and 3 d weighed dietary records between 4 and 18 years of age. BP was measured using a mercury sphygmomanometer (Mercuro 300, WelchAllyn) and salt intake was determined based on 24 h Na excretion. The intra-individual change in salt intake was almost significantly associated with the change in systolic BP (SBP, P= 0·06) and marginally (P= 0·09) with that in diastolic BP (DBP) in puberty, but not in pre-puberty. A 1 g/d increase in salt intake was associated with a 0·2 mmHg increase in SBP. In pre-puberty, but not in puberty, differences in FVI between children predicted between-person variations in SBP and DBP (P= 0·03). Corresponding findings were obtained for 24 h K excretion (a urinary indicator for FVI). A 100 g/d lower FVI was related to a 0·4 mmHg higher BP value. In conclusion, in healthy children and adolescents with BP in the low-normal range, both salt intake and FVI may already start to influence BP, although at a small magnitude. The potential importance of establishing healthy eating habits in childhood for later BP development emphasises the role of higher FVI and lower salt intake in the prevention of hypertension in the long run.

Childhood blood pressure trends and risk factors for high blood pressure: the NHANES experience 1988-2008

The obesity epidemic in children makes it plausible that prevalence rates of elevated blood pressure (BP) are increasing over time. Yet, previous literature is inconsistent because of small sample sizes. Also, it is unclear whether adjusting for risk factors can explain longitudinal trends in prevalence of elevated BP. Thus, we analyzed a population-based sample of 3248 children in National Health and Nutrition Examination Survey (NHANES) III (1988-1994) and 8388 children in continuous NHANES (1999-2008), aged 8 to 17 years. Our main outcome measure was elevated BP (systolic BP or diastolic BP ≥ 90th percentile or systolic BP/diastolic BP ≥ 120/80 mm Hg). We found that the prevalence of elevated BP increased from NHANES III to NHANES 1999-2008 (Boys: 15.8% to 19.2%, P=0.057; Girls: 8.2% to 12.6%, P=0.007). Body mass index (Q4 versus Q1; odds ratio=2.00; P<0.001), waist circumference (Q4 versus Q1; odds ratio=2.14; P<0.001), and sodium (Na) intake (≥ 3450 mg versus <2300 mg/2000 calories; odds ratio=1.36; P=0.024) were independently associated with prevalence of elevated BP. Also, mean systolic BP, but not diastolic BP, was associated with increased Na intake in children (quintile 5 [Q5] versus quintile 1 [Q1] of Na intake; β=1.25 ± 0.58; P=0.034). In conclusion, we demonstrate an association between high Na intake and elevated BP in children. After adjustment for age, sex, race/ethnicity, body mass index, waist circumference, and sodium intake, odds ratio for elevated BP in NHANES 1999-2008 versus NHANES III=1.27, P=0.069.

Sodium intake and blood pressure among US children and adolescents

OBJECTIVE

To assess the association between usual dietary sodium intake and blood pressure among US children and adolescents, overall and by weight status.

METHODS

Children and adolescents aged 8 to 18 years (n = 6235) who participated in NHANES 2003-2008 comprised the sample. Subjects' usual sodium intake was estimated by using multiple 24-hour dietary recalls. Linear or logistic regression was used to examine association between sodium intake and blood pressure or risk for pre-high blood pressure and high blood pressure (pre-HBP/HPB).

RESULTS

Study subjects consumed an average of 3387 mg/day of sodium, and 37% were overweight/obese. Each 1000 mg per day sodium intake was associated with an increased SD score of 0.097 (95% confidence interval [CI] 0.006-0.188, ∼1.0 mm Hg) in systolic blood pressure (SBP) among all subjects and 0.141 (95% CI: -0.010 to 0.298, ∼1.5 mm Hg) increase among overweight/obese subjects. Mean adjusted SBP increased progressively with sodium intake quartile, from 106.2 mm Hg (95% CI: 105.1-107.3) to 108.8 mm Hg (95% CI: 107.5-110.1) overall (P = .010) and from 109.0 mm Hg (95% CI: 107.2-110.8) to 112.8 mm Hg (95% CI: 110.7-114.9; P = .037) among those overweight/obese. Adjusted odds ratios comparing risk for pre-HBP/HPB among subjects in the highest versus lowest sodium intake quartile were 2.0 (95% CI: 0.95-4.1, P = .062) overall and 3.5 (95% CI: 1.3-9.2, P = .013) among those overweight/obese. Sodium intake and weight status appeared to have synergistic effects on risk for pre-HBP/HPB (relative excess risk for interaction = 0.29 (95% CI: 0.01-0.90, P < .05).

CONCLUSIONS

Sodium intake is positively associated with SBP and risk for pre-HBP/HPB among US children and adolescents, and this association may be stronger among those who are overweight/obese.

Patterns of sodium and potassium excretion and blood pressure in the African Diaspora

Habitual levels of dietary sodium and potassium are correlated with age-related increases in blood pressure (BP) and likely have a role in this phenomenon. Although extensive published evidence exists from randomized trials, relatively few large-scale community surveys with multiple 24-h urine collections have been reported. We obtained three 24-h samples from 2704 individuals from Nigeria, Jamaica and the United States to evaluate patterns of intake and within-person relationships with BP. The average (±s.d.) age and weight of the participants across all the three sites were 39.9±8.6 years and 76.1±21.2 kg, respectively, and 55% of the total participants were females. Sodium excretion increased across the East-West gradient (for example, 123.9±54.6, 134.1±48.8, 176.6±71.0 (±s.d.) mmol, Nigeria, Jamaica and US, respectively), whereas potassium was essentially unchanged (for example, 46.3±22.9, 40.7±16.1, 44.7±16.4 (±s.d.) mmol, respectively). In multivariate analyses both sodium (positively) and potassium (negatively) were strongly correlated with BP (P<0.001); quantitatively the association was stronger, and more consistent in each site individually, for potassium. The within-population day-to-day variation was also greater for sodium than for potassium. Among each population group, a significant correlation was observed between sodium and urine volume, supporting the prior finding of sodium as a determinant of fluid intake in free-living individuals. These data confirm the consistency with the possible role of dietary electrolytes as hypertension risk factors, reinforcing the relevance of potassium in these populations.

A critical review of aspirin in the secondary prevention of noncardioembolic ischaemic stroke

Both secondary prevention (such as lifestyle modifications, pharmacotherapy or surgery) and an understanding of the influence of risk factors (including the different aetiologic mechanisms of cerebral ischaemia) play a pivotal role in reducing the burden of recurrent stroke. Regarding the types of preventative treatments available, variations exist across all clinical studies, including differences in target populations (including the type of cerebral ischaemia), risk factors, length of follow-up, drop-out rates and outcomes, which makes translating the results of clinical trials to individual patients difficult. However, with such limitations in mind, this critical albeit nonsystematic review, which compared aspirin with other antiplatelets and in combination with other drugs, showed that the benefit from aspirin treatment is consistently shown in ischaemic stroke, while harms are limited. Furthermore, no definite superiority is apparent across different antiplatelet therapies. Dual antiplatelet regimens may expose to a slight but measurable higher risk of haemorrhagic complications, perhaps in selective groups of patients (i.e. those with severe small-vessel disease or in selective racial groups). Based on our analysis, the indication of aspirin as the first-line choice, also recommended by several acknowledged international or national guidelines, may be confirmed. However, the complex nature of patients at risk of recurrent ischaemic stroke necessitates a comprehensive approach, which should be driven by the primary care physician, whose role is central to successful actions for secondary stroke prevention.

Reducing population salt intake worldwide: from evidence to implementation

Raised blood pressure is a major cause of cardiovascular disease, responsible for 62% of stroke and 49% of coronary heart disease. There is overwhelming evidence that dietary salt is the major cause of raised blood pressure and that a reduction in salt intake lowers blood pressure, thereby, reducing blood pressure-related diseases. Several lines of evidence including ecological, population, and prospective cohort studies, as well as outcome trials, demonstrate that a reduction in salt intake is related to a lower risk of cardiovascular disease. Increasing evidence also suggests that a high salt intake may directly increase the risk of stroke, left ventricular hypertrophy, and renal disease; is associated with obesity through soft drink consumption; is related to renal stones and osteoporosis; is linked to the severity of asthma; and is probably a major cause of stomach cancer. In most developed countries, a reduction in salt intake can be achieved by a gradual and sustained reduction in the amount of salt added to foods by the food industry. In other countries where most of the salt consumed comes from salt added during cooking or from sauces, a public health campaign is needed to encourage consumers to use less salt. Several countries have already reduced salt intake. The challenge now is to spread this out to all other countries. A modest reduction in population salt intake worldwide will result in a major improvement in public health.

Salt intakes around the world: implications for public health

BACKGROUND

High levels of dietary sodium (consumed as common salt, sodium chloride) are associated with raised blood pressure and adverse cardiovascular health. Despite this, public health efforts to reduce sodium consumption remain limited to a few countries. Comprehensive, contemporaneous sodium intake data from around the world are needed to inform national/international public health initiatives to reduce sodium consumption.

METHODS

Use of standardized 24-h sodium excretion estimates for adults from the international INTERSALT (1985-87) and INTERMAP (1996-99) studies, and recent dietary and urinary sodium data from observational or interventional studies--identified by a comprehensive search of peer-reviewed and 'grey' literature--presented separately for adults and children. Review of methods for the estimation of sodium intake/excretion. Main food sources of sodium are presented for several Asian, European and Northern American countries, including previously unpublished INTERMAP data.

RESULTS

Sodium intakes around the world are well in excess of physiological need (i.e. 10-20 mmol/day). Most adult populations have mean sodium intakes >100 mmol/day, and for many (particularly the Asian countries) mean intakes are >200 mmol/day. Possible exceptions include estimates from Cameroon, Ghana, Samoa, Spain, Taiwan, Tanzania, Uganda and Venezuela, though methodologies were sub-optimal and samples were not nationally representative. Sodium intakes were commonly >100 mmol/day in children over 5 years old, and increased with age. In European and Northern American countries, sodium intake is dominated by sodium added in manufactured foods ( approximately 75% of intake). Cereals and baked goods were the single largest contributor to dietary sodium intake in UK and US adults. In Japan and China, salt added at home (in cooking and at the table) and soy sauce were the largest sources.

CONCLUSIONS

Unfavourably high sodium intakes remain prevalent around the world. Sources of dietary sodium vary largely worldwide. If policies for salt reduction at the population level are to be effective, policy development and implementation needs to target the main source of dietary sodium in the various populations.

A comprehensive review on salt and health and current experience of worldwide salt reduction programmes

Cardiovascular disease (CVD) is the leading cause of death and disability worldwide. Raised blood pressure (BP), cholesterol and smoking, are the major risk factors. Among these, raised BP is the most important cause, accounting for 62% of strokes and 49% of coronary heart disease. Importantly, the risk is throughout the range of BP, starting at systolic 115 mm Hg. There is strong evidence that our current consumption of salt is the major factor increasing BP and thereby CVD. Furthermore, a high salt diet may have direct harmful effects independent of its effect on BP, for example, increasing the risk of stroke, left ventricular hypertrophy and renal disease. Increasing evidence also suggests that salt intake is related to obesity through soft drink consumption, associated with renal stones and osteoporosis and is probably a major cause of stomach cancer. In most developed countries, a reduction in salt intake can be achieved by a gradual and sustained reduction in the amount of salt added to food by the food industry. In other countries where most of the salt consumed comes from salt added during cooking or from sauces, a public health campaign is needed to encourage consumers to use less salt. Several countries have already reduced salt intake, for example, Japan (1960-1970), Finland (1975 onwards) and now the United Kingdom. The challenge is to spread this out to all other countries. A modest reduction in population salt intake worldwide will result in a major improvement in public health.

Salt and blood pressure in children and adolescents

To study the relationship between salt intake and blood pressure in children and adolescents, we analysed the data of a large cross-sectional study (the National Diet and Nutrition Survey for young people), which was carried out in Great Britain in 1997 in a nationally representative sample of children aged between 4 and 18 years. A total of 1658 participants had both salt intake and blood pressure recorded. Salt intake was assessed by a 7-day dietary record. The average salt intake, which did not include salt added in cooking or at the table, was 4.7+/-0.2 g/day at the age of 4 years. With increasing age, there was an increase in salt intake, and by the age of 18 years, salt intake was 6.8+/-0.2 g/day. There was a significant association of salt intake with systolic blood pressure as well as with pulse pressure after adjusting for age, sex, body mass index and dietary potassium intake. An increase of 1 g/day in salt intake was related to an increase of 0.4 mm Hg in systolic and 0.6 mm Hg in pulse pressure. The magnitude of the association with systolic blood pressure is very similar to that observed in a recent meta-analysis of controlled trials where salt intake was reduced. The consistent finding of our present analysis of a random sample of free-living individuals with that from controlled salt reduction trials provides further support for a reduction in salt intake in children and adolescents.

Diet and blood pressure in children

PURPOSE OF REVIEW

The prevalence of hypertension among children in the US is increasing in concert with rising obesity rates. Leading health organizations agree that elevated blood pressure should be managed in children; however, data on the relation between diet and lifestyle and blood pressure in this age group are sparse and controversial. The purpose of this review is to summarize the current evidence regarding nutrients, foods, and dietary patterns and their role in blood pressure elevation and in the treatment of pediatric hypertension.

RECENT FINDINGS

There is clear evidence that avoidance of excess weight gain in early life is important for the prevention of future hypertension and that weight reduction is an important therapeutic intervention for the prevention and treatment of hypertension in overweight children. Similarly, reduction in dietary sodium may be beneficial for children who are salt sensitive, but this trait cannot be easily measured. Children who were breast-fed or consume a diet rich in fruits, vegetables, and dairy foods tend to have lower blood pressure in adolescence. How these foods lower blood pressure is unclear.

SUMMARY

Data supporting the efficacy of dietary interventions for preventing or treating high blood pressure are limited. Future studies should emphasize adequate sample size, adjustment for confounding factors, use of standardized blood pressure techniques, and random assignment of children in intervention trials. Additionally, because adherence to dietary interventions may be particularly problematic among children, innovative nutrition intervention approaches are needed that address the unique needs and circumstances of this age group.

Ethnicity, education, and blood pressure in Cuba

The causes of variation in hypertension risk by ethnicity and educational level are not well understood. To gain further insight into this issue in a nonindustrialized country, a population-based sample of 1,667 persons aged 15-74 years was recruited in Cienfuegos, Cuba. In this 2001-2002 study, interviewers classified 29% of participants as Black or mulatto and 71% as White. Educational attainment was stratified at the median number of school years. Compared with White women, non-White women had higher blood pressures (3.0/1.7, systolic blood pressure/diastolic blood pressure) and a higher prevalence of hypertension (24%, 95% confidence interval: 20, 28 vs. 15%, 95% confidence interval: 12, 18). Among men, no differences in blood pressure were observed by ethnicity. Men with a lower level of education had a 14% lower risk of hypertension compared with men above the median. However, women with a lower level of education had a 24% increase in risk. The effect of education was equally strong among Whites alone and when occupation was used for stratification. No variation was observed for body mass index or self-reported health behaviors by ethnicity or education. The narrower ethnic gradient in hypertension prevalence than seen in North America and the gender-specific social status effect, in the context of relatively equal living conditions, suggest that the influence of psychosocial stressors may be specific to cultural contexts.

Early life determinants of adult blood pressure

PURPOSE OF REVIEW

While treating high blood pressure in middle age is beneficial in terms of reducing the occurrence of cardiovascular disease, treated and well controlled hypertensive adults still have a substantial excess mortality and reduced survival compared with normotensives. Therefore, identification of the means of preventing hypertension in earlier life is an important objective. There is increasing evidence that adult blood pressure is determined by a range of characteristics from the intrauterine period, through infancy and childhood. The purpose of this review is to provide a summary of the current evidence concerning the early life determinants of adult blood pressure.

RECENT FINDINGS

Children from poorer socioeconomic positions, those whose mothers experience pregnancy-induced hypertension, those whose mothers smoke throughout pregnancy, those with low birthweight, who are not breast-fed, who have high sodium diets in infancy and who are obese in childhood or adolescence tend to have higher blood pressure in adulthood. However, the mechanisms linking these early life factors to later blood pressure and the most appropriate means of preventing adult hypertension by intervening in early life are unclear.

SUMMARY

There is clear evidence that early life factors are important determinants of adult blood pressure. However, there is a need for randomized trials with sufficient resources for long-term follow-up to assess the effects that interventions such as preventing pregnancy-induced hypertension, reducing maternal smoking, increasing breast-feeding, reducing salt consumption in infancy and preventing childhood obesity have on adult blood pressure and cardiovascular disease.

Arachidonic acid metabolism in nicotine-treated rats and nicotine-incubated rabbit aortic smooth muscle cells

1. The changes in plasma levels of thromboxane-B2 (TXB2) and 6-keto-prostaglandin-F1 alpha (6-keto-PGF1 alpha) were examined in rats given 5, 25, 50 or 100 micrograms/mL nicotine in drinking water for 10 days. 2. The effect of nicotine on prostacyclin (PGI2) synthesis from endogenous arachidonic acid by cultured rabbit aortic smooth muscle cells was also studied. 3. Plasma levels of TXB2 were increased dose-dependently by treatment for 10 day with nicotine. 4. 6-Keto-PGF1 alpha values were lowered dose-dependently, both in the plasma of nicotine-treated rats and in rabbit aortic smooth muscle cells incubated with the alkaloid. 5. The results suggest that endogenous synthesis of thromboxane-A2 and PGI2, as reflected by TXB2 and 6-keto-PGF1 alpha levels, respectively, is influenced by nicotine treatment. These findings may be related to cardiovascular diseases associated with cigarette smoking, but further studies are needed.

Sodium and blood pressure: the puzzling results of intrapopulation epidemiologic studies

Most intrapopulation epidemiologic studies have been unable to find a significant association between sodium intake and blood pressure. The researchers have offered 2 opposing explanations: the hypothesis of the genetic susceptibility to sodium and the hypothesis of a weak association in general population. The evidence for and against each hypothesis is reviewed. The direction of future research is suggested.

Hypertension, coronary artery disease and insulin resistance--linked disorders with an impact on treatment

Coronary artery disease is a very common disorder for which hypertension is a well-recognized risk factor. However many trials of antihypertensive therapy have failed to demonstrate a reduction in the incidence of coronary events. One explanation is that hypertension is a disorder associated with hyperinsulinaemia, obesity and non-insulin dependent diabetes. Furthermore certain antihypertensive drugs, notably thiazide diuretics, increase the hyperinsulinaemia and thereby increase one of the other coronary risk factors. In this review the links between hypertension and hyperinsulinaemia are explored and the mechanisms whereby an increased plasma insulin can lead to the more rapid development of coronary artery disease are explained. These observations may influence the choice of drugs used to treat hypertension.

Population based data on urinary excretion of calcium, magnesium, oxalate, phosphate and uric acid in children from Cimitile (southern Italy)

Population based data on 24-h urinary excretion of calcium, oxalate, magnesium, phosphate, uric acid and creatinine were collected from 220 children (aged 3-16 years) living in Cimitile, Campania, southern Italy. Mean excretion rates for 7 days were correlated with age, body weight, body mass index and height. The prevalence of hypercalciuria (greater than 4 mg/kg body weight) and of hyperoxaluria (greater than 60 mg/day) were 9.1% and 1.8%, respectively. The same 20 children were also identified as hypercalciuric when a calcium/creatinine ratio of greater than 0.15 was considered. No significant differences between boys and girls were found in the urinary excretion of the five constituents implicated in urolithiasis. The study data provide additional childhood reference values for urinary excretion of compounds related to stone formation.

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

The relations between 24 hour urinary electrolyte excretion and blood pressure were studied in 10,079 men and women aged 20-59 sampled from 52 centres around the world based on a highly standardised protocol with central training of observers, a central laboratory, and extensive quality control. Relations between electrolyte excretion and blood pressure were studied in individual subjects within each centre and the results of these regression analyses pooled for all 52 centres. Relations between population median electrolyte values and population blood pressure values were also analysed across the 52 centres. Sodium excretion ranged from 0.2 mmol/24 h (Yanomamo Indians, Brazil) to 242 mmol/24 h (north China). In individual subjects (within centres) it was significantly related to blood pressure. Four centres found very low sodium excretion, low blood pressure, and little or no upward slope of blood pressure with age. Across the other 48 centres sodium was significantly related to the slope of blood pressure with age but not to median blood pressure or prevalence of high blood pressure. Potassium excretion was negatively correlated with blood pressure in individual subjects after adjustment for confounding variables. Across centres there was no consistent association. The relation of sodium to potassium ratio to blood pressure followed a pattern similar to that of sodium. Body mass index and heavy alcohol intake had strong, significant independent relations with blood pressure in individual subjects.

Management of hypertension in high school students by using new salt titrator tape

In a blood pressure screening program involving 6589 high school students, 180 male (4.7%) and 17 female (0.6%) students were identified as borderline hypertensive. The 174 hypertensive male adolescents studied further showed pathophysiological features such as a significantly higher frequency of obesity, higher 24-hour urinary sodium excretion, higher hematocrit value, higher sodium and lower potassium concentration in red blood cells, and higher ouabain-sensitive sodium efflux compared with the control group (231 male students; p less than 0.05). When used alone, the ordinary 10-week period of counseling about a low salt diet failed to significantly reduce the blood pressure of hypertensive students. However, when education and counseling efforts were combined with self-monitoring of salt (chloride) excretion in overnight urine samples using a new salt titrator tape developed in our laboratory, 24-hour urinary sodium excretion, weight, and blood pressure decreased significantly over 10 weeks (mean reduction: 52 mEq/day for 24-hour urinary sodium excretion, 1.7 kg for weight, 12/7 mm Hg for blood pressure). These results indicate that blood pressure of borderline hypertensive adolescents could be effectively reduced with this nonpharmacological method of dietary education. Such systematic management might be of importance for the prevention of essential hypertension.

[Salt and blood pressure]

Current information on the relationship between sodium and blood-pressure regulation is reviewed from the point of view of epidemiological, clinical and experimental research, as well as evidence from intervention studies. Among other cations, calcium also has an influence on blood pressure. Epidemiological studies in particular are handicapped by the difficulties inherent in measuring salt intake in individuals with adequate accuracy. Despite remaining uncertainties and the need for further investigation, available data from different sources and a considerable number of studies justify the recommendation that the average daily salt intake of the population should not exceed 5 g (NaCl), corresponding to 85 meq or mmol of sodium (Na). This is a goal which should be approached gradually, paying simultaneous attention to other factors likely to be involved in the primary prevention of hypertension, especially overweight, and the maintenance of a sufficient supply of iodine and fluor for which salt is used as a vehicle in many countries.

Childhood antecedents of adult degenerative disease

The pathogenetic links between diet and diseases such as hypertension and atherosclerosis remain the subject of much controversy. This article reviews the evidence about the relationship between diet and these two widespread adult conditions, proposes an approach for their early recognition, examines the rationale and safety of dietary changes, and formulates specific recommendations.

The efficacy of quantitative and qualitative chloride titrators in the estimation of human salt intake

We evaluated the utility of chloride titrator sticks for facilitating the assessment of dietary salt intake, in a systematic series of clinical trials. These inexpensive devices were applied daily to 24-h or nocturnal urine specimens, thereby avoiding the inter- and intra-subject variability in salt excretion which confounds the use of occasional 24-h urine collections. Chloride and sodium concentrations in urine were highly correlated (r greater than 0.92) in either nocturnal, diurnal, or 24-h collections. The quantitative chloride titrator estimates and measured chloride concentrations were highly correlated as well (r greater than 0.99). The qualitative chloride titrator was graded on a simple scale, and was successfully employed by outpatients attempting to limit their salt intake. Commonly used antihypertensive medications did not interfere with the determinations. Additional chloride intake, such as supplemental potassium chloride, interfered with estimates of salt ingestion, but if the daily amount of potassium chloride supplement was constant, adjustments in interpretation could be made. Renal insufficiency introduced a systematic over-estimation of salt intake by the qualitative chloride tirator, but only at high salt intakes. Relative estimates of salt intake in subjects with renal failure were still possible. We conclude that chloride titrators can facilitate the management of patients who require a prescribed salt intake.

Tonic heart rate level, social class and antisocial behaviour in adolescents

On the basis of previous empirical research it was hypothesised that (a) antisocial behaviour in adolescence would be characterised by lower tonic heart rate levels and (b) any such relationship would be particularly borne out in the higher social classes where the 'social push' towards antisociality may be relatively weaker. These predictions were tested by relating tonic heart rate levels in a sample of 15 year old male schoolchildren to self-report and teacher ratings of antisocial behaviour/undersocialization. An 'antisocial' group was found to have significantly lower heart rate levels than a 'prosocial' group. Several analyses on high and low class groups resulted in a significant low heart rate/antisociality relationship in the high classes only. It was speculated that the heart rate/antisociality relationship may be mediated by somatotype, or alternatively that low levels in high class antisocials may reflect a vagal passive adaptation to mildly aversive events.

Family history of hypertension and rates of sodium transport: absence of an association in population-based studies

In a series of population-based studies, the relationship between a family history of hypertension and sodium transport was examined. In the total sample of 417 individuals, and in each sex-race-specific sub-sample, no significant differences were noted in red cell sodium-lithium countertransport, sodium concentration, or passive leak. A higher proportion of hypertensives was not found in the group with a positive family history, and blood pressures were only slightly higher in those--compared to those without--a positive family history. If family history of hypertension is associated with levels of countertransport, it would appear that the relationship is weak in the general population.

Technical considerations for platelet aggregation and related problems

Platelet aggregation generally is ordered by the physician to evaluate platelet function in hemorrhagic or thrombotic disorders. Malfunction of the platelet may be the result of an intrinsic congenital defect or an acquired problem induced by drugs or certain circulating plasma factors. It is necessary to obtain information from the patient with respect to family history, drug ingestion, physical or mental stress. In addition, other laboratory studies should be obtained to rule out general coagulation disorders affecting the plasma factors. A bleeding time will be helpful in establishing the severity of any platelet dysfunction. Technical considerations with regard to the preparation of the samples are of primary importance in determining platelet aggregation. Aggregating studies require the use of a variety of binding agents. (Studies on shape change, adhesion of platelets, release of platelet granule substance, and or lysis with extrusion of cytoplasmic constituents may be helpful in certain cases.) Instrumentation for platelet aggregation presently is available in many hospitals. The technical factors to be considered for routine aggregation studies include the type and strength of anticoagulant, centrifugation technique used in preparing the platelet-rich and platelet-poor plasma, platelet concentration, time of storage of the sample after venipuncture and after centrifugation, temperature, and the mixing of the sample. In general, critical concentrations of each reagent should be employed to improve the discrimination capability of the assay. Small differences in response may be obliterated by using excessive concentrations of a given reagent. Comparison in response to the test platelets with control platelets is best done at the same time by performing the aggregation in a dual instrument so that handling procedures will be identical and artifactual differences eliminated.

Dietary salt and blood pressure

Research evidence on the role of dietary sodium in the etiology and pathogenesis of hypertension is briefly reviewed. This matter is assuming new importance at present, given new data on the efficacy of normalization of blood pressure for adults with so-called "mild" hypertension (average diastolic 90-104 mm Hg), hence the need for safe nutritional-hygienic alternatives to years-long drug treatment for millions of people with such hypertension. Two trials by the authors deal with some unresolved questions in this area. The first, a preliminary study, involved 21 lacto-ovo-vegetarian high school students living in a boarding school. With decrease in daily Na intake from 216 to 72 meq for the experimental compared with the control group, red blood cell Na concentration was significantly lower in the former; systolic pressure was slightly but not significantly lower. The second trial, the Primary Prevention of Hypertension, involves over 200 hypertension-prone persons aged 30-44, and explores the ability in the experimental group to reduce blood pressure and prevent development of hypertension by safe nutritional-hygienic means (weight reduction, dietary Na decrease, avoidance of excess alcohol, rhythmic exercise). Initial results at 6 months are presented. Trials on the prevention and control of hypertension by nonpharmacologic means, including reduced Na intake, and involving analyses of the inter-relationships among dietary Na, other dietary factors, Na metabolism, and blood pressure in samples from different population strata, are an important present-day research need.

Dietary sodium and arterial pressure: problems of studies within a single population

The nature of the relationship between dietary sodium and arterial pressure remains uncertain, largely because of the difficulty of investigating this relationship within a single population. There are two main hypotheses: one requires that hypertensive and normotensive patients differ in their sodium intake, the other that they differ in their susceptibility to dietary sodium. Neither hypothesis has been fully explored. In this paper the types of study required to test each hypothesis are considered and published work is used to illustrate the problems of interpreting studies in this field.

The selective lipid-lowering effect of vegetarianism on low density lipoproteins in a cross-over experiment

In a cross-over experiment the effect of short-term vegetarianism on serum lipids, lipoproteins and apoproteins was studied. The experimental diet was free of animal products, with the exception of skim milk, and consequently low in saturated fat and cholesterol. Fifteen free-living individuals were randomly assigned to 3-week periods on either the experimental diet or a control diet which closely approximated the usual intake in the U.S.A. Significant reductions in total cholesterol (12.5%), low density lipoprotein cholesterol (14.7%), and apo B (13.2%) were observed, accompanied by a non-significant decrease in high density lipoprotein cholesterol (10%), apo A-I (3%) and a non-significant increase in apo-II (4%). These data suggest that a fat-modified diet low in total fat, saturated fat and cholesterol, and moderate (not high) in polyunsaturated fat may not lower HDL-C or its apoproteins as much as a diet high in polyunsaturated fat, while having similar effects on LDL-C, and would therefore be preferable as the basis for primary prevention of atherosclerosis.

Water sodium and blood pressure in rural school children

Blood pressures were measured in 326 boys and 309 girls, 12 to 14 yr of age, who attended schools in six rural towns with water sodium levels ranging from 1.46 to 9.69 mmol/L. Although there were significant differences between mean blood pressure levels in children living in the six towns, they did not appear to result from differences in water sodium levels. Children who lived on farms and who drank low-sodium rain water did not have lower blood pressures than children who lived in the towns. The estimated intake of sodium from drinking water in the towns varied between 1.5 and 11.6 mmol/day and represented between 1.2% and 10.4% of the estimated daily sodium intake. No effect of water sodium level on urinary sodium excretion was found. Blood pressure levels showed significant positive relationships with pulse rate, body height and weight, Quetelet's index, mid-upperarm circumference, and triceps skinfold thickness. Diastolic blood pressures in girls were inversely related to the measure of physical activity. Control of these variables, where relevant, by covariance analysis did not uncover any relationship between water sodium level and blood pressure.

Methodological problems in characterizing an individual's plasma glucose level

Two methodological problems in characterizing an individual's plasma glucose level are examined in this study. First, how large is the intra-individual variation of an individual's 1-hr post-load glucose level and for this estimated intra-individual variation what are the probabilities of misclassifying individuals based on a one-time measurement only of glucose level? Second, do different tests-i.e. fasting, 1-hr, 2 hr post-load, GTT-yield consistent ranking for the same individual? The first of these was explored with data on subsamples from the Chicago Peoples Gas Company (PG) study and the Chicago Heart Association Detection Project in Industry (CHA) study; the second, with data from the Chicago Coronary Prevention Evaluation Program (CPEP). For both the PG and CHA studies, the estimated ratios of the intra- to inter-individual variances were generally higher for post-load plasma glucose than blood pressure, heart rate, weight and serum uric acid. The conditional probabilities of misclassifying individuals into quintiles or deciles based on one measurement of 1-hr post-load glucose were also estimated from these data. These estimated probabilities indicated that the possible attenuation due to intra-individual variation cannot abolish a strong association; however, it may create some problem if the relationship is not very strong. Furthermore, both rank correlation and quintile classification analyses show that fasting, 1-hr and 2-hr plasma glucose level characterize individuals differently. Thus it is possible that the inconsistent results of previous studies, all using a one-time measure of plasma glucose, are partially due to the large intra-individual variation of this variable, and the use of methods that are not highly consistent in their classification of individuals.