The dominance of salt in manufactured food in the sodium intake of affluent societies

Ethnic differences in intake and excretion of sodium, potassium, calcium and magnesium in South Africans

OBJECTIVES

To determine any differences in the urinary excretion and dietary intake of sodium, potassium, magnesium and calcium intake in three South African ethnic groups, and to assess whether the blood pressure-cation association varies according to ethnic status.

DESIGN

A cross-sectional study of 325 black, white and mixed-ancestry men and women, conveniently sampled in Cape Town. Twenty-four-hour urine samples were collected on three separate occasions for assessment of urinary electrolytes, and three 24-h dietary recalls for the corresponding urine collection times were administered by two trained fieldworkers. Para-amino benzoic acid was used as a marker of the completeness of urine collection.

RESULTS

Mean urinary sodium values equate to a daily salt (sodium chloride) intake of 7.8, 8.5 and 9.5 g in black, mixed-ancestry and white individuals, respectively. In normotensive individuals, black and mixed-ancestry subjects had significantly lower median urinary sodium concentrations than white subjects, but these differences were not evident between black and white hypertensive subjects. No ethnic differences were found for urinary potassium, except for mixed-ancestry normotensive individuals having a lower excretion than white normotensive individuals. Urinary magnesium excretion did not differ across ethnic groups. In both normotensive and hypertensive individuals, urinary calcium concentrations differed between all three groups, with black subjects having the lowest values, approximately less than half those of white subjects.

CONCLUSION

White normotensive subjects in Cape Town have higher habitual intakes of sodium, but also higher calcium intakes than their black and mixed-ancestry counterparts. Dietary differences may contribute to ethnic-related differences in blood pressure.

Increasing the iodine concentration in the Swiss iodized salt program markedly improved iodine status in pregnant women and children: a 5-y prospective national study

BACKGROUND

Many industrialized countries struggle to maintain adequate iodine intake because of changes in dietary habits and the food supply. In Switzerland, because of declining iodine intakes in children and pregnant women, the iodine concentration in table salt was increased from 15 to 20 mg/kg.

OBJECTIVE

We evaluated Swiss iodine nutrition after the 1999 increase in the salt iodine concentration.

DESIGN

In 1999 and 2004, a 3-stage probability proportionate-to-size cluster sampling was done to obtain a representative national sample of primary schoolchildren and pregnant women. Urine and household salt were collected for iodine measurement. The frequency of elevated thyrotropin concentrations found in the newborn screening program was evaluated before and after the increase.

RESULTS

In 1999, median urinary iodine (UI) concentrations among children (n = 610) and pregnant women (n = 511) were 115 microg/L (range: 5-413 microg/L) and 138 microg/L (range: 5-1881 microg/L), respectively, which indicated marginal iodine status. In 2004, median UI concentrations among children (n = 386) and pregnant women (n = 279) were 141 microg/L (range: 0-516 microg/L) and 249 microg/L (range: 8-995 microg/L), respectively (P < 0.01). Newborn thyrotropin concentrations >5 mU/L decreased from 2.9% in 1992-1998 (n = 259 035) to 1.7% in 1999-2004 (n = 218 665) (P < 0.0001).

CONCLUSIONS

A 25% increase in iodine concentration in iodized table salt markedly improved iodine status in Switzerland, which showed the value of monitoring and adjusting iodine concentrations in national salt programs. The frequency of newborn thyrotropin concentrations >5 mU/L appears to be a sensitive indicator of iodine nutrition during pregnancy.

Diet and blood pressure in South Africa: Intake of foods containing sodium, potassium, calcium, and magnesium in three ethnic groups

OBJECTIVES

We investigated whether habitual intakes of sodium (Na), potassium, magnesium, and calcium differ across South African ethnic groups, assessed the proportion of Na intake, which is discretionary, and identified which food sources were the major contributors to Na intake.

METHODS

This was a cross-sectional study of 325 black, white, and mixed ancestry hypertensive and normotensive subjects. Three repeated 24-h urine samples were collected for assessment of urinary Na, and three corresponding 24-h dietary recalls were administered by trained fieldworkers. Blood pressure and weight were measured at each visit. Secondary analyses were performed on existing dietary databases obtained from four regional surveys undertaken in South African adults.

RESULTS

Mean urinary Na excretion values equated to daily salt (NaCl) intakes of 7.8, 8.5, and 9.5 g in black, mixed ancestry, and white subjects, respectively (P < 0.05). Between 33% and 46% of total Na intake was discretionary, and, of the non-discretionary sources, bread was the single greatest contributor to Na intake in all groups. Ethnic differences in calcium intake were evident, with black subjects having particularly low intakes. Urban versus rural differences existed with respect to sources of dietary Na, with greater than 70% of total non-discretionary Na being provided by bread and cereals in rural black South Africans compared with 49% to 54% in urban dwellers.

CONCLUSION

White South Africans have higher habitual intakes of Na, but also higher calcium intakes, than their black and mixed ancestry counterparts. All ethnic groups had Na intakes in excess of 6 g/d of salt, whereas potassium intakes in all groups were below the recommended level of 90 mM/d. Dietary differences may contribute to ethnically related differences in blood pressure.

Origins and evolution of the Western diet: health implications for the 21st century

There is growing awareness that the profound changes in the environment (eg, in diet and other lifestyle conditions) that began with the introduction of agriculture and animal husbandry approximately 10000 y ago occurred too recently on an evolutionary time scale for the human genome to adjust. In conjunction with this discordance between our ancient, genetically determined biology and the nutritional, cultural, and activity patterns of contemporary Western populations, many of the so-called diseases of civilization have emerged. In particular, food staples and food-processing procedures introduced during the Neolithic and Industrial Periods have fundamentally altered 7 crucial nutritional characteristics of ancestral hominin diets: 1) glycemic load, 2) fatty acid composition, 3) macronutrient composition, 4) micronutrient density, 5) acid-base balance, 6) sodium-potassium ratio, and 7) fiber content. The evolutionary collision of our ancient genome with the nutritional qualities of recently introduced foods may underlie many of the chronic diseases of Western civilization.

Reducing the public health burden from elevated blood pressure levels in the United States by lowering intake of dietary sodium

Elevated blood pressure levels are a major cause of heart disease and stroke. Healthy People 2010 established objectives to reduce mortality from these diseases by 20% and to reduce the major causal factors associated with these elevated levels, such as excess sodium intake. The American public consumes far more sodium than is needed, most of which is added by food manufacturers and restaurants. In November 2002, the American Public Health Association adopted a policy resolution calling for a 50% reduction in sodium in the nation's food supply over the next 10 years. Such a reduction would greatly enhance the chances of attaining the Healthy People 2010 objectives and would save at least 150 000 lives annually. This issue warrants public health intervention.

A one-quarter reduction in the salt content of bread can be made without detection

OBJECTIVE

To determine if it is possible to deliver a one-quarter reduction in the sodium content of bread without detection.

DESIGN

Single-blind, randomized, controlled trial.

SETTING

The Royal North Shore Hospital in Sydney, Australia.

PARTICIPANTS

One-hundred and ten volunteers from the hospital staff that completed 94% of scheduled assessments.

INTERVENTION

Six consecutive weeks of bread with usual sodium content or six consecutive weeks of bread with cumulating 5% reductions in sodium content each week.

MAIN OUTCOME MEASURE

The proportion of participants reporting a difference in the salt content of the study bread from week to week.

RESULTS

The intervention group were no more likely than the control group to report a difference in the salt content of the bread from week to week (P=0.8). Similarly, there were no differences between randomized groups in the scores for flavour (P=0.08) or liking of the bread (P=0.95) over the study follow-up period. However, the saltiness scores recorded on a visual analogue scale did decline in the intervention group compared with the control group (P=0.01)

CONCLUSIONS

A one-quarter reduction in the sodium content of white bread can be delivered over a short time period, while maintaining consumer acceptance. Over the long term, and particularly if achieved for multiple foods, a decrease in sodium content of this magnitude would be expected to reduce population levels of blood pressure and the risks of stroke and heart attack.

Dietary electrolytes and hypertension in the elderly

The effect of age on older hypertensive patient's blood pressure response to increased sodium intake is well known. Salt sensitivity which does increase with age and the decrease in renal function limiting the ability of aged kidney to excrete sodium load are major factors, responsible for rise in blood pressure during Na consumption in the elderly. Clinical studies encourage salt reduction with and without weight loss. Although potassium consumption is highly recommended, one should be aware of potassium overload in the elderly.

Calcium diglutamate improves taste characteristics of lower-salt soup

OBJECTIVE

: To ascertain (1) whether the taste characteristics of a conventionally-salted (150 mM NaCl) soup can be reproduced in soups of substantially lower NaCl level with the help of added glutamate, and (2) whether calcium diglutamate (CDG) is equivalent to monosodium glutamate (MSG) in its effect on the taste of soup.

DESIGN

: Cross-sectional, with multiple measurements on each subject.

SETTING

: Healthy university students.

SUBJECTS

: A total of 107 volunteers, recruited by on-campus advertising.

METHODS

: Subjects tasted 32 soups, with all possible combinations of four NaCl concentrations (0-150 mM), four glutamate levels (0-43 mM), and two glutamate types (MSG, CDG).

MAIN OUTCOME MEASURES

: Ratings of each soup on six scales (liking, flavour-intensity, familiarity, naturalness of taste, richness of taste, saltiness).

RESULTS

: A 50 or 85 mM NaCl soup with added CDG or MSG is rated as high as, or higher than, a 150 mM NaCl soup free of added glutamate on five of the six scales (the exception being saltiness). CDG and MSG have equivalent effects.

CONCLUSIONS

: Addition of glutamate allows substantial reductions in Na content of soup, without significant deterioration of taste. CDG and MSG have equivalent effects, but use of CDG permits a greater reduction in Na intake.

A question of balance: nutrition, health and gastronomy

Given the higher proportion of manufactured foods now available which meet current dietary recommendations, the food supply in developed countries like Australia could be said to be "healthier". Yet the "health" of the diet is often achieved at the expense of the "health" of the environment since ecological problems created a current food production and distribution methods remain unaddressed. Further, nutritional modifications which produce foods that are low in fat, sugar, salt and high in fibre do not necessarily address the concerns consumers have about the food supply. An emphasis solely on the physical health of populations, through improved diet, is out of keeping with current views on health which recognise the importance of overall well-being. Through the development of the concept of "sustaining gastronomy", consumers, food manufacturers and producers, and food regulators can better address the problems inherent in the food system, including those of an environmental nature.

The Hobart Salt Study 1995: few meet national sodium intake target

OBJECTIVE

To estimate 24-hour sodium and potassium excretion in an urban Australian population.

DESIGN AND SETTING

Cross-sectional survey of an urban population in Hobart, Tasmania, in 1995.

PARTICIPANTS

Systematic sample (87 men, 107 women) from the Commonwealth Electoral Roll of people aged 18-70 years on 30 June 1995 whose residential address was within 10 km of the Hobart General Post Office.

MAIN OUTCOME MEASURE

Conformity with the national target for sodium intake for the year 2000 of < or = 100 mmol/day.

RESULTS

The target was met by 6% of men and 36% of women. This difference between the sexes was significant (P < 0.001), while differences between age groups and socioeconomic levels were not significant.

CONCLUSION

Our findings confirm the low level of conformity with the national sodium target reported by the handful of Australian studies over the past decade. Given the major community costs associated with hypertension, our results highlight the need for effective and properly monitored action to reduce sodium intakes.

The potentiality and practicality of a 'salt-free' diet for the prevention and amelioration of human disorders

The potential of a salt-free diet, which restricts sodium intake to 10 mmol/day, for the prevention and amelioration of human diseases and conditions, may be considerable. Several human disorders may be the result of dietary-salt-generated high-bodily-sodium motility and fluid retention, this being incompatible with the maintenance of bodily homeostasis whenever the body is subjected to stress. Equally importantly, the present-day impracticalities of adopting a 'salt-free' diet appear man-made, and therefore soluble once a sufficiency of purpose exists.

The instability of dietary iodine supply over time in an affluent society

In the Bernese region, where goiter was formerly endemic, alimentary salt has been supplemented by increasing amounts of potassium iodide (KI): 5, 10, 20 mg KI/kg in 1922, 1965 and 1980 respectively. Ioduria rose from < 30 micrograms I/g creatinine in 1920 to > 100 micrograms I/g creatinine in the 1980s. In 1992 ioduria was estimated in 55 healthy volunteers (group A and individual B) and 234 thyroid carcinoma patients after thyroidectomy: hypothyroid patients with (C) and without thyroid remnants (D) and euthyroid patients on T4 substitution (E). The arithmetic mean iodine excretion of the healthy volunteers in group A and individual B was found to be 87 +/- 40 micrograms I/g creatinine. This is insufficient according to the recommendations of the WHO. In all groups, the iodine excretion reached the recommended level only in some members: 24% (A, B), 19% (C), 38% (D) and 81% (E). It was thought in the 1980s that in a formerly iodine-deficient society, iodinated salt would continue to provide an adequate supply of iodine. However, iodine intake in this affluent society has proved to be unstable. This can be attributed to modifications of eating habits, which include a reduction of total salt consumption, combined with a growing consumption of manufactured food of cosmopolitan origin, prepared using salt containing little or no iodine.

Consumer acceptance of foods lower in sodium

OBJECTIVE

To assess the magnitude of sodium reduction that can be made without significantly changing the perception of saltiness and acceptability of a broad range of common food items.

DESIGN

The investigation was carried out in two phases. Military and civilian volunteers (N = 190 in study 1; N = 380 in study 2) from the US Army Natick Research, Development and Engineering Center rated the saltiness and acceptability of foods containing differing sodium concentrations.

SETTING

Consumers rated food items in the sensory testing laboratory.

INTERVENTION

"Regular" and "low-sodium" entrees were rated for saltiness and acceptability in study 1. Prepared food, commercially prepared food, and beverages containing various concentrations of sodium were rated for saltiness and acceptability in study 2.

STATISTICAL ANALYSES PERFORMED

Results were analyzed using Pearson correlation coefficients, Student's t test, and analysis of variance.

RESULTS

The perception of saltiness increased as the concentration of sodium increased. Acceptance ratings varied considerably over a broad range of sodium concentrations, which indicates that the relationship was product specific. Results suggest that a reduction of one third or more in added sodium can be made to some foods without significantly affecting consumer acceptance.

APPLICATIONS

The sodium content of food can be reduced by consumer-guided food engineering and food preparation. Alterations in food preparation and product formulation, in conjunction with alterations in diet, can be effective methods for reducing sodium consumption.

The effect of potassium supplementation in persons with a high-normal blood pressure. Results from phase I of the Trials of Hypertension Prevention (TOHP). Trials of Hypertension Prevention (TOHP) Collaborative Research Group

We conducted a randomized, double-blind, placebo-controlled trial of oral potassium chloride supplementation (60 mmol/d) in 353 men and women with an initial average diastolic blood pressure between 80 and 89 mm Hg. In the active (n = 178) compared to the placebo (n = 175) treatment group, the urinary potassium level was significantly (p < 0.001) increased by an average of 44.0 and 42.3 mmol/24 h following 3 and 6 months of therapy, respectively. Compared to placebo, active treatment was associated with a small (mean = 1.8 mm Hg) but significant (p = 0.04) reduction in diastolic blood pressure following 3 months of therapy. Following 6 months, however, this apparent treatment effect had virtually disappeared (mean reduction in diastolic blood pressure = 0.3 mm Hg). There was no significant effect of potassium supplementation on systolic blood pressure at either follow-up visit. There was a significant, independent, dose-response relationship between change in both 24-hour urinary potassium excretion and urinary sodium-potassium ratio and the corresponding change in diastolic blood pressure (-1.49 mm Hg for the highest versus the lowest quartile of change in urinary potassium excretion.

Non-pharmacological treatment of hypertension

This paper represents a compilation of the latest scientific research on the non-pharmacological management of hypertension to help practitioners manage this highly prevalent disease. In this regard, recent evidence suggests that nonpharmacological approaches--particularly weight reduction, salt restriction, moderation of alcohol consumption, reduction of cholesterol intake and exercise--may lower elevated pressure and improve the efficacy of pharmacological agents. Non-pharmacological therapy should be stressed for the future treatment of hypertension.

Relative contributions of dietary sodium sources

Information on the relative contributions of all dietary sodium (Na) sources is needed to assess the potential efficacy of manipulating the component parts in efforts to implement current recommendations to reduce Na intake in the population. The present study quantified the contributions of inherently food-borne, processing-added, table, cooking, and water sources in 62 adults who were regular users of discretionary salt to allow such an assessment. Seven-day dietary records, potable water collections, and preweighted salt shakers were used to estimate Na intake. Na added during processing contributed 77% of total intake, 11.6% was derived from Na inherent to food, and water was a trivial source. The observed table (6.2%) and cooking (5.1%) values may overestimate the contribution of these sources in the general population due to sample characteristics, yet they were still markedly lower than previously reported values. These findings, coupled with similar observations from other studies, indicate that reduction of discretionary salt will contribute little to moderation of total Na intake in the population.

By how much does dietary salt reduction lower blood pressure? III--Analysis of data from trials of salt reduction

OBJECTIVE

To determine whether the reduction in blood pressure achieved in trials of dietary salt reduction is quantitatively consistent with estimates derived from blood pressure and sodium intake in different populations, and, if so, to estimate the impact of reducing dietary salt on mortality from stroke and ischaemic heart disease.

DESIGN

Analysis of the results of 68 crossover trials and 10 randomised controlled trials of dietary salt reduction.

MAIN OUTCOME MEASURE

Comparison of observed reductions in systolic blood pressure for each trial with predicted values calculated from between population analysis.

RESULTS

In the 45 trials in which salt reduction lasted four weeks or less the observed reductions in blood pressure were less than those predicted, with the difference between observed and predicted reductions being greatest in the trials of shortest duration. In the 33 trials lasting five weeks or longer the predicted reductions in individual trials closely matched a wide range of observed reductions. This applied for all age groups and for people with both high and normal levels of blood pressure. In people aged 50-59 years a reduction in daily sodium intake of 50 mmol (about 3 g of salt), attainable by moderate dietary salt reduction would, after a few weeks, lower systolic blood pressure by an average of 5 mm Hg, and by 7 mm Hg in those with high blood pressure (170 mm Hg); diastolic blood pressure would be lowered by about half as much. It is estimated that such a reduction in salt intake by a whole Western population would reduce the incidence of stroke by 22% and of ischaemic heart disease by 16% [corrected].

CONCLUSIONS

The results from the trials support the estimates from the observational data in the accompanying two papers. The effect of universal moderate dietary salt reduction on mortality from stroke and ischaemic heart disease would be substantial--larger, indeed, than could be achieved by fully implementing recommended policy for treating high blood pressure with drugs. However, reduction also in the amount of salt added to processed foods would lower blood pressure by at least twice as much and prevent some 75,000 [corrected] deaths a year in Britain as well as much disability.

Research and policy directions. Salt and blood pressure

The relation between dietary intake of sodium chloride and blood pressure levels remains controversial. The critical questions concern whether there is a susceptible subgroup at risk of elevated blood pressure because of sodium chloride consumption. If there is such a subgroup, what is its size and how can it be identified? Further clinical trials are needed to determine the long-term effects of sodium chloride reduction on blood pressure. The risk of disease, including stroke and coronary heart disease, is linear with blood pressure levels. A small change in blood pressure can have a relatively large impact on disease, even within the normal range of blood pressure.

Limited compensation by table salt for reduced salt within a meal

Sixteen subjects, all of whom had said in a preliminary questionnaire that they normally added table salt to foods, were fed standard meals in the laboratory over 10 days. The meals were identical, except that on 5 days the meal had no added salt (containing 0.46 g sodium chloride) or had salt added to a level of 5.09 g. They were allowed free access to salt pots with the meals and used an average of 1.40 g table salt with the unsalted meal and 0.36 g with the salted meal, thus compensating for 22% of the difference in salt content of the meal. There was no difference in water consumption between the two types of meal. Nutrient intake from the rest of the diet did not differ between periods with high and low salt meals. The failure to compensate more fully for reduced salt in the foods can be attributed to the greater availability of table salt for perception; less table salt than salt incorporated in the foods is therefore required. Reduction of salt concentrations in purchased foods would be unlikely to be fully replaced by the consumer adding table salt.

Avoidance of dietary sodium--a simple questionnaire

Patients who are advised to reduce their sodium intake need intensive counselling and regular feedback on their progress. Urinary tests can indicate a high sodium intake, but the dietary source remains unknown until the patient has answered detailed questions. We have developed a sodium-intake check-list for this purpose and have investigated whether it is comprehensive enough to replace the urinary test. The most heavily-salted foods in the typical Western diet are listed in 21 questions, which are to be answered in relation to the previous three days' intake with a frequency rating of "zero" to "eight or more"; the check-list score is the sum of the scores for all 21 items. For 190 college students who were eating their regular diet, the scores were distributed normally and internally were reliable (Cronbach coefficient alpha = 0.75). They were significantly different (P less than 0.001) from the scores of the 40 persons who were attending a low-sodium advisory service. The range of the urinary sodium excretion rate for 39 persons in the latter group was 9-181 mmol/24 h. The correlation between the urinary sodium excretion results and those of the check-list was r = 0.701, which is an acceptable figure considering that the urine excretion data were, for practical reasons, derived from a single 24-h sample. As the absolute sodium excretion is itself only an estimate of dietary behaviour, we consider that this simple questionnaire, as based on a three-day recall, is useful in the management of patients who are ingesting "salt-free" diets, both as an adjunct and as an alternative to urinary testing in routine clinical use.