Biomedical subjects
T C Beard
Publications and source records attributed to T C Beard.
Greenhouse effect, renal calculi, and salt.
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Hypertension after Intersalt: prospects for prevention.
Special methods of statistical analysis of the Intersalt data permitted a better comparison between populations and between age groups than was previously possible, but these methods led to an exclusive focus on the distribution of blood pressure (BP) rather than on the prevalence of hypertension. Big changes in prevalence that accompany small changes in mean BP were implied but not illustrated. A plot of prevalence against log Na excretion from the tabulated data suggests that a Na excretion rate greater than 100 mmol/day could not be recommended under any circumstances. However, a rate less than 40 mmol/day would be expected to prevent hypertension and to prevent the BP from rising with age. From the intersalt data, an intermediate range of Na excretion of 40-100 or 50-100 mmol/day, which are public health targets in Australia and the United States, respectively, would be expected to be protective in the presence of other aspects of a healthy lifestyle, especially if the K intake preserves the natural Na/K ratio (less than or equal to 1.0).
A salt-hypertension hypothesis.
In urban Australia, the risk of retiring with hypertension is greater than 40%, and the basic abnormality--a rise in blood pressure (BP) with age--is almost universal. A hypothesis linking this with salt, therefore, concerns everyone. The diet of early humans was unsalted, and the Na content of breast milk (6 mmol/kg) shows how little NaCl is needed even during the most rapid period of growth. The hypothesis that the hypertonic concentration needed to preserve food causes the BP to rise with age is based partly on the normotensive status of contemporary "salt-free" societies and partly on experimental evidence. "Salt-free" populations seldom use alcohol and happen to be lean and active, with a low fat intake and largely vegetarian diet, but Westerners with similar virtues do not escape hypertension. Ideally, the prophylactic effect of avoiding salt would be ascertained in large-scale, prospective trials, but practical, ethical and, economic factors impose serious design problems. Nevertheless, a public health intervention based on this hypothesis would be incomplete without a serious attempt to measure the outcome.
Effect of salt restriction on hypertension.
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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.
Calcium carbonate tablets.
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Human behaviour and the ethics of coercion.
There is an assumption that legislation against unhealthy behaviour would be unethical, or at best unenforceable and counterproductive. However, the ethics of coercion depend on the manner in which such coercion is introduced, the essential precondition being wide, favourable community consensus. Two recent Australian examples have been the Victorian seat-belt legislation and the Tasmanian hydatid campaign. Hydatid control in Tasmania began with a voluntary campaign in the farming community which led to a popular demand for government intervention. In response to community pressure, the State Department of Agriculture introduced control measures with a stepwise increase in coercion that began with a voluntary dog-testing programme, and proceeded to a compulsory test and later to the quarantine of infected dogs. Ultimately, quarantine was extended to premises with a higher-than-average residual prevalence in sheep. Today, hydatid disease has almost disappeared in livestock. As no new human case of hydatid disease has been diagnosed in a person of under 10 years of age since 1972, or in one of under 20 years of age since 1976, human infection probably ceased by 1972. Legislation today could control the composition of processed food (for example, the salt content), or establish compulsory testing for human immunodeficiency virus antibodies. The necessary consensus could be the specific objective of health education during a voluntary phase.
Relevance of the salt-hypertension hypothesis to the community control of hypertension.
By applying the Framingham data to the distribution of blood pressure in the Australian population, it can be shown that almost half the morbidity from strokes and ischaemic heart disease that is attributable to blood pressure would be expected to occur in subjects who are "normotensive" by the current World Health Organization (WHO) definition. The steadily increasing risk with every increment of diastolic blood pressure above 70 mmHg supports the contention that the dividing line between "normotension" and "hypertension" is artefactual, and that the basic problem is the tendency for blood pressure levels to rise with age. The rise with age occurs exclusively and invariably in salt-eating societies, and the most promising hypothesis that is awaiting evaluation is that this rise could largely be prevented by the universal adoption of the Australian Recommended Dietary Intake for sodium of 40-100 mmol/day. Two factors that may limit the prophylactic effect of avoiding salt are self-sustaining hypertension and teratogenic hypertension, both of which are seen when rats are fed salt. In Australia and several other countries it is already official policy to recommend a lower intake of salt. Although we support this, we consider that interventions with such massive implications are incomplete without a serious attempt to measure the outcome. Double-blind conditions would be impossible, but a large-scale population-based trial with randomization would be feasible. The first stage of the trial should consist of a campaign of salt reduction in patients with established hypertension, in collaboration with medical practitioners and the food industry, because it is unrealistic to expect good dietary compliance from several thousand "normotensive" persons until those who want to avoid salt are catered for more adequately.
Danger of overmedication with no-added-salt diets.
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Verapamil, low-sodium regimens, and blood pressure.
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Salt and hypertension in pregnancy.
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Changing rural behaviour: two campaigns that worked.
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Spontaneous remission and its significance for trials in primary prevention of hypertension.
The hypothesis that salted food can cause hypertension must be tested prospectively to see if unsalted food protects non-hypertensive persons. The first of two feasibility studies has confirmed that established hypertension can show spontaneous remission on unsalted food. We now report the preliminary findings of a second feasibility study to test whether a clinic for hypertension can attract self-referred non-hypertensive people interested in preventing hypertension by changing their diet. A total of 874 applicants have attended at least one pre-entry visit. We report data from the first 176 participants who completed the feasibility study lasting 12 weeks. Of these 110 were non-hypertensive people and 93 (84.5%) would be prepared to remain on unsalted food for five years.
Randomised controlled trial of a no-added-sodium diet for mild hypertension.
90 patients on medication for mild hypertension were randomly allocated to diet and control groups and kept under surveillance by their own doctors every 2 weeks for 12 weeks to test the short-term effectiveness of a diet free from sodium additives as an alternative to medication. Mean urinary sodium excretion was reduced 37.0 mmol/24 h in the diet group and 161.0 mmol/24 h in the control group, with average K/Na ratios of 3.9 and 0.50. Both groups had a fall in mean systolic and diastolic blood pressure, but the diet group finished on half of the initial amount of medication, with 1 patient in 3 off medication and 4 out of 5 having either stopped or reduced the dose. The control group remained on almost the full amount of medication, with 2 patients out of 3 having made no reduction. The diet group had a mean weight loss of 2.1 kg, a rise in serum potassium, and a fall in serum bicarbonate. There was no increase in overall frequency of muscle cramp, and the diet group reported feeling happier, less depressed, and less dependent on analgesics. Two-thirds of the diet group intend to continue to diet indefinitely. Reduction of sodium intake permitted drug treatment to be substantially reduced without side-effects or loss of blood-pressure control.