Moderate dietary salt reduction and salt taste perception of normotensive individuals with family history of hypertension

NUTRITION RESEARCH, Vol. 5, pp. 1309-1319, 1985 0271-5317/85 $3.00 + .00 Printed in the USA. Copyright (c) 1986 Pergamon Press Ltd. All rights reserved.

MODERATE DIETARY SALT REDUCTION AND SALT TASTE PERCEPTION OF NORMOTENSIVE INDIVIDUALS WITH FAMILY HISTORY OF HYPERTENSION l Mabel Mei-Ying Chan*, Jenene G. Garey*, Barbara Levine*, Jean E. McRae~', Irma Terpenningt *Department of Home Economics and Nutrition, New York University, Washington Square, New York, NY 10003; *Clinical Nutrition Research Unit (NIH5PO1CA29502), New York Hospital, Cornell Medical Center, Memorial Sloan-Kettering Cancer Center, New York, NY 10021; tAT&T Bell Laboratories, Murray Hill, NJ 07974

ABSTRACT The purpose of this study is to examine any effects of dietary salt reduction possibly achieved by normotensive, non-institutionalized individuals with a family history of hypertension. Twelve subjects (7 males and 5 females) between 18 and 24 years of age were instructed to follow a reduced sodium diet for 10 weeks. The following data on salt taste perception and physical characteristics were collected during the pre-diet period, during the sixth week of the reduced sodium diet, and during its tenth week. 9 taste tests of salt water, broth, and rice, rating salt intensity and preference 9 body weight 9 blood pressure 9 24-hour urinary sodium, potassium, calcium, and creatinine 9 whole saliva sodium, potassium, and calcium 9 3-day dietary surveys of sodium, potassium, calcium, and caloric intake The data were analyzed using analyses of variance and covariance, and graphical displays. No significant trial effect was found for any response except systolic blood pressure and salivary calcium; the means of these decreased linearly throughout the study. Subjects with high pre-diet calcium (urinary, salivary, and dietary) and high urinary potassium tended to perceive greater saltiness and prefer less saltiness than subjects with low baseline levels. KEY WORDS: moderate dietary salt reduction, salt, taste, hypertension

1. Addressall correspondenceto Mabel M. Chan, Departmentof HomeEconomicsand Nutrition, New York University, Washington Square, New York,NY 10003.

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1. INTRODUCTION Epidemiological and experimental data have linked excessive intake of salt to elevated blood pressure(l). In 1975 it was estimated that about 18% of U.S. adults between the ages of 25 and 74 were hypertensive(2). Because of the prevalence of this disorder, the U.S. Senate Select Committee on Nutrition and Human Needs proposed targeting adults' intake of salt to about 5 g per day(3) (4), compared to the currently prevalent intake of 8-12 g per day in the U. S.(5) (6). The human requirement for salt has been estimated as less than 0.5 g per day(7). The portion of salt appetite beyond physiological need probably is acquired via experience and/or learning(8) and possibly may be altered. Recent studies(9) (10) have shown that the preferred level of salt in food may depend on dietary NaCI intake in healthy adults, with a decrease in Na intake resulting in a lower preferred level. The purpose of this study is to examine any effects of reduction in dietary NaC1 intake possibly achieved by normotensive, non-institutionalized individuals with a family history of hypertension. This population was chosen because the tendency to develop hypertension may have a strong genetic component(ll) (12) (13). Effects on salt taste perception and preference were of interest. 2. METHODS 2.1 Subjects

Twelve individuals were recruited from students at one dining facility within a large urban university. They were nonsmokers, seven males and five females between 18 and 24 years of age. These subjects were normotensive with a family history of hypertension. The subjects regularly ate at least two meals daily at the dining facility. During the study period most menu items offered at the facility by the university dining contract company contained reduced NaC1, enabling subjects to comply easily with the reduced Na regime. The subjects followed their regular diet during the first four weeks of the study (pre-diet period). Then they were counseled for one hour about a reduced Na diet, and instructed to consume 5 g or less of NaC1 (2 g Na) per day during the next 10 weeks. The reduced Na menu at the dining hall was introduced when the moderate NaCI dietary regime began, and continued until the end of the study. Concurrently, a food acceptability and preference study(14) was conducted, using all students eating in this facility. It showed no effect of NaCI reduction on quantity of food consumed or on the hedonic rating of the food. 2.2 Collection of the Data

All procedures were approved by the university committee on research with human subjects. Data were collected at trial 1, during the pre-diet month when subjects were on their regular diets, trial 2, during the sixth week on the moderate NaCI diet, and trial 3, during the tenth week on the moderate NaCI diet. At each trial, taste tests of salt intensity and preference were conducted for several concentrations of NaCI in water, chicken broth, and rice. Weight and blood pressure were measured at each trial. During the following seven days, each subject recorded the quantity eaten and drunk on two week days and one weekend day. Three-day dietary intake data were calculated from these records using food composition tables(15) and nutrient information supplied by the contract company, based on their analysis of recipes used. Whole mouth saliva was collected before each taste test. Subjects drooled into a beaker for 5 minutes. Saliva was diluted with distilled deionized water. Na and K were measured

DIETARY SALT REDUCTION, TASTE

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using flame photometry and Ca was measured by atomic absorption spectroscopy. At each trial 24-hour urine was collected. An unannounced urine sample also was collected early in the first month of the moderate salt diet, between scheduled trials 1 and 2. The subjects were asked to begin a 24-hour urine collection the next day. This lack of prior knowledge of the collection prevented them from making short-term changes in dietary Na. Each urine sample was analyzed for Na, K, Ca, and creatinine. 2.3 Taste Tests At each trial, the pleasantness and intensity of NaCI in water, broth, and rice were marked on horizontal lines 100 mm in length. Only the ends of the lines were labeled, serving as anchor points. The labels were "dislike extremely" and "like extremely" for preference and "not salty at all" and "extremely salty" for intensity of salt. A rating consisted of the distance in millimeters from the left anchor point (dislike or unsalty) to the subject's mark. To minimize cross-checking of ratings, response forms were placed in an envelope after each sample was evaluated. Seven concentrations of NaCI (reagent grade) in water and in low sodium chicken broth (Health Valley Inc., CA.) in equal log steps ranging from 0.06 M to 0.85 M were used as two stimuli. Five concentrations of NaCI in rice (Minute Rice, General Foods Corp, N.Y.) in equal log steps from 0.5% to 3.3% provided a third stimulus. The rice was prepared according to Mattes et al(16). Portion sizes were about 10 ml each of the solutions and half a tablespoon of cooked rice. Broths were warmed to 53 ~ C; salt water and rice were presented at room temperature. The order of presenting the three stimuli was randomized. Each concentration was presented twice in predetermined random order with the restriction that all concentrations must occur before any replicate. The subjects rated each sample for preference, and then intensity of the salt taste. They rinsed with deionized water once between solution samples and twice between rice samples; swallowing was not permitted. 2.4 Analysis of the Data Of primary interest were changes in hedonic and salt intensity ratings across trials, and corresponding changes in physical and dietary characteristics. These responses could be affected by the experimental factors of trials, stimuli, subjects, NaCI concentrations, and replicates. Analyses of variance (anovas) and analyses of covariance were used to summarize and quantify effects. Graphical displays(17) were used to explore and understand the behavior of the data. Numerical and graphical results were obtained using S(18), a UNIXTi-based system for graphics and data analysis. Differences between replicates provided measures of noise, identification of discrepant values, and checks of assumptions underlying tests of significance. Analyses of variance and covariance quantified the effects of trials and stimuli against the noise of subjects and replicates. Responses in the anovas were the intercepts and slopes of lines fitted to saltiness ratings, and breakpoints. 3. RF~ULTS 3.1 Physical Measurements Table 1 summarizes the physical and dietary :..~easurements of 11 subjects during the study. One subject missed trial 2 and was omitted from all analyses.

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TABLE 1 PHYSICAL AND DIETARY DATA Means of 11 Subjects Trial 1 1. Body weight kg 67.5 2. Blood pressure, systolic 113.2 3. Blood pressure, diastolic 67.9 4. Urinary Na mEq/24hr 119.0 5. Urinary K mEq/24hr 52.5 6. Urinary Ca ppm 123.5 7. Urinary creatinine g/24hr 1.5 8. Salivary Na ppm 156.8 9. Salivary K ppm 773 10. Salivary Ca ppm 52.6 11. Dietary Na g 3.6 12. Dietary K g 3.1 13. Dietary Ca mg 1078 14. Dietary kcal 2434

Extra Trial 2 67.4 107.1 67.9 91.0 96.0 45.9 53.1 107.5 143.0 1.4 1.4 129.6 651 31.6 2.7 3.0 1051 2186

Trial 3 67.3 105.4 70.2 97.6 51.6 96.5 1.4 133.8 637 24.7 2.9 2.9 1103 2316

Std Error* Range of a of Mean Data 0.3 48-87 1.5 90-125 2.2 53-84 9.3 24.6-242.5 4.2 17.0-97.8 17.0 8.7-314.9 0.1 0.4-2.5 16.7 23-414 56 188-936,1279 7.6 7.8-144.9 0.3 1.0-9.3 0.2 1.0-5.8 75 405-3075 96 1145-3997

*Based on the subject by trial interaction The only significant physical or dietary changes during the study were systolic blood pressure and salivary Ca, which decreased at each trial. Urinary, salivary, and dietary N a showed no significant differences among trials although all of the values were lower in the period of reduced NaC1 intake. Despite dietary instruction and the availability of low N a food items at the dining facility, the subjects did not significantly reduce their N a intake. The Na, K, Ca, and creatinine values of the unannounced urine sample were not different from the means of trials 1 and 2.

3.2 Replicates The second replicate was rated saltier and liked more than the first, suggesting a possible carry-over effect despite the water rinse between samples. Breakpoint replicate differences showed preference for a saltier second replicate. These effects were consistent over trials, concentrations, and stimuli. Differences between replicate ratings (saltiness and hedonic) were less consistent at middle concentrations of the solutions. Apparently at middle concentrations the saltiness rankings became less distinctive, and the preferences therefore uncertain. Consistency between replicates of hedonic ratings of the solutions varied significantly across trials but did not increase throughout the study, as might have resulted from increasing familiarity with study procedures.

3.3 Saltiness Ratings Columns 1 and 2 of Figure 1 show median, quartiles, and range 2 of saltiness ratings across Each box plot displays both the central tendency (the median) and the variability in a set of data. The median is the horizontal line within a box. The quartiles are the ends of a box. The range is denoted by the ends of the dashed vertical lines unless outlying values(18), plotted by the character "o", are present. The outliers are not used in determining the box.

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subjects and replicates for each concentration and stimulus for trials 1 and 3. The medians show strong linear relationships with log concentration. Thus the two parameters of a line (intercept and slope) can adequately represent the effect of 7 or 5 concentrations. A least squares line was fitted to the mean of the two replicates for each trial, stimulus, and subject. Since the actual log concentrations were almost equally spaced, simple representations of the independent variables were used, namely - 3 ( 1 ) 3 for the solutions and -3(1.5)3 for rice. The intercept of the line measured the saltiness intensity; specifically for these regressions it is the fitted saltiness rating at the middle concentration. The slope of the line measured the magnitude of the perceived changes in saltiness; the greater the rated difference between low and high concentrations, the steeper the slope. The anova of intercepts showed no effect of trials. Stimuli varied significantly (left plot of Figure 2), with mean intercepts of water 5.59, broth 5.42, and rice 4.08 (standard error 0.16). Thus rice was rated as less salty than the solutions. Subjects disagreed significantly as to whether water or broth was saltier. The anova of slopes also found no effect of trials. Again stimuli showed a significant effect (right plot of Figure 2), with means of water 1.39, broth 1.44, and rice 0.93 (standard error 0.076). The extreme concentrations of rice did not differ as much as those of the solutions.

3.4 Breakpoints Hedonic ratings are expected to have a maximum at some most-liked concentration, denoted as the breakpoint. Columns 3 and 4 of Figure 1 show non-linear relationships between preference rating and concentration. When the maxima are poorly defined or nonexistent, a breakpoint was selected subjectively for each set of 7 or 5 hedonic ratings. No trial effect was found in anovas of breakpoints effect was significant (left plot of Figure 3), with broth, and rice. The most preferred concentration concentration for all stimuli. The mean breakpoint water or broth.

averaged over replicates. The stimulus mean breakpoints increasing for water, is significantly below the middle NaC1 was significantly saltier for rice than for

Linear correlations between breakpoints and the corresponding saltiness ratings were significant for water and rice but not for broth, although relationships were clearly positive for all stimuli. An anova of the breakpoint saltiness ratings showed no effect of stimulus or trial. The lack of any stimulus effect can be seen in the right plot of Figure 3. The most preferred concentration received a saltiness rating of 3.46 (standard error 0.17) on the scale of 0 to 10, averaged across trials, stimuli, and subjects.

3.5 Stylized Summary Figure 4 offers a stylized summary of the results found for breakpoints and saltiness ratings. The lines are located according to the actual results given by the data; so are the curves, but such clear hedonic maxima were not found in the data. Salt water and broth are combined, since they do not differ. Rice and the solutions differ in their breakpoints, shown as curves, and in their saltiness ratings, shown as solid lines. The hedonic ratings of the breakpoints show no stimulus effect. Neither do the saltiness ratings that correspond to breakpoints, as substantiated by the dotted horizontal lines that do not differ.

3.6 Covariates Pre-diet variation among subjects contributes to the noise over which trial effects must be detected. A eovariate can be used to adjust data to a constant level of the covariate, thus removing a source of variation that may be masking effects of interest. Each of the physical

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average breakpoint FIG. 4. Styfized Saltiness Lines, Hedonic Curves, and Breakpoints, drawn according to parameters calculated from the data. and dietary characteristics was the covariate in covariance anovas measuring the adjusted effects of trials. The anovas found no real effects. Another approach to removing effects of baseline physical variation is to define groups of subjects having comparable physical characteristics during the pre-diet period. Subjects were grouped according to low and high urinary Na, K, and Ca, dietary Ca, or salivary Ca during the pre-diet period. Males and females also were compared. Anovas of low and high baseline groups found no trial effect. However, the means between groups do differ for those responses and stimuli specified in Table 2, which shows t statistics associated with significant differences between (high-low) group means, or between means of (males-females). The groups differ for all stimuli averaged and for one or more individual stimuli, for most responses. For K and Ca, these differences consistently indicate that the high baseline groups tend to perceive greater saltiness, and prefer less saltiness, than these low groups. For urinary Na the saltiness effect is in the opposite direction, due to an effect from rice only. The high Ca groups tend to think that concentrations change more than do the low Ca groups, except for the opposing effect from water for dietary Ca. 4. DISCUSSION

The taste responses were comparable to previous reports(9) (I0), although no trial effect was found in either the hedonic or intensity ratings for NaCI in water, broth, or rice. This result harmonizes with the lack of significant change in the Na intake. Bertino et al(9) indicate that change in taste response depends on at least two factors -amount of sodium reduction and length of the dietary period. The present study of I0

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TABLE 2 SIGNIFICANT* DIFFERENCES BETWEEN BASELINE GROUPS Significant* t of Group Differences Water Broth Rice Averaged Urinary Na Intercept Urinary K Intercept Breakpoint Urinary Ca Intercept Slope Breakpoint Dietary Ca Intercept Slope Breakpoint Salivary Ca Intercept Slope Males -Females Intercept Slope

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*p < 0.05. The t statistics are shown for all group differences that exceed the 5% significance level. weeks surpassed the lengths when changes in taste response were observed in other studies. As examples, hedonic and intensity ratings of salts in soup were altered for individuals on 1.73 g Na per day for three and one half weeks(9), and preliminary results(19) suggest that adults on 1.6 g Na per day added significantly less salt in ad libitum mixing tasks after eight weeks on the diet. But all studies reporting taste change involved low Na intake varying from 0.99 g(10) to 1.73 g(9) per day. The subjects of the present study consumed about 2.7 g per day, rather than the target of 2.0 g. This apparently was not low enough to produce any significant change in salt taste perception. Interviews with the participants indicated that they had no difficulty in following the dietary instructions. An acceptability study(14) suggests that the reduced Na menu was well l~eceived, so the subjects had little reason to deviate from the reduced NaCI regime. Half of the subjects had dietary Na intake of 2.36 g or less in the pre-diet period, which is a moderately low level. Therefore they could not reduce dietary Na as easily nor as much as persons initially consuming higher levels of Na. When the responses from the subjects were categorized into low and high baseline groups according to the pre-diet levels of Na, K, and Ca, several significant differences between groups were found. Most high groups tended to give higher salt intensity ratings and prefer lower salt concentrations than low groups. Since McCarron et al(20) have observed a correlation between low dietary Ca and hypertension, further investigation of the relationship between Ca status and salt taste perception might prove interesting.

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ACKNOWLEDGEMENTS The authors are grateful to Dr. M. D. Simko for reviewing the proposal of this study, and to Maureen Suplee and Melissa Rosenblatt for their assistance. Health Valley Natural Foods provided the low sodium chicken broth. REFERENCES 1. TOBIAN L. The Relationship of Salt to Hypertension. Am. J. Clin. Nutr. 1979; 32: 2739-48. 2. USDHH, PHS, NCHS. Hypertension in Adults 25-74 Years of Age, United States, 1971-1975. Vital and Health Statistics, DHHS Publication No. (PHS) 81-1671, Series 11, No. 221. Washington DC: US Govt Printing Office, 1981. 3. USDA, US HEW. Nutrition and Your Health. Dietary Guidelines for Americans. Washington DC: US Govt Printing Office, 1980. 4. Food and Nutrition Board, National Research Council. Toward Healthful Diets. Washington DC: National Academy of Sciences, 1980. 5. Life Sciences Research Office, Federation of American Societies for Experimental Biology. Tentative Evaluation of the Health Aspects of Sodium Chloride and Potassium Chloride as Food Ingredients. SCOGS-102. Prepared for the Bureau of Foods, Food and Drug Administration, Department of Health, Education, and Welfare. Washington DC: 1978. 6. FORSYTHE RH, MILLER RA. Salt in Processed Foods. In: Kare MR, Fregly MJ~, Bernard AA, ed. Biological and Behavioral Aspects of Salt Intake. New York: Academic Press Inc., 1980. 7. Food and Nutrition Board, National Research Council. Recommended Dietary Allowances. 9th edition. Washington DC: National Academy of Sciences, 1980. 8. MENSELY GR, BATTARBEE HD. Sodium and Potassium. In: Nutrition Reviews, Present Knowledge in Nutrition. 4th edition. New York: Nutrition Foundation, 1976: 259-79. 9. BERTINO M, BEAUCHAMP GK, RISKEY DR, ENGELMAN K. Taste Perception in Three Individuals on a Low Sodium Diet. Appetite 1981; 2: 67-73. 10. BERTINO M, BEAUCHAMP GK, ENGELMAN K. Long-term Reduction in Dietary Sodium Alters the Taste of Salt. Am. J. Clin. Nutr. 1982; 36:1134-44. 11. SWAYE PS, GIFFORD RW, BERRETTONI JN. Dietary Salt and Essential Hylx:rtension. Am. J. Cardiol. 1972; 29: 33-38. 12. THOMAS CB. Genetic Patterns of Hypertension in Man. In: Onesti G, Kim KE, Moyer JD, ed. Hypertension: Mechanisms and Management. New York: Grune and Stratton, 1972: 6773. 13. ZINNER SH, LEVY PS, KASS EH. Familial Aggregation of Blood Pressure in Childhood. New Engl. J. Med. 1971; 284: 401-4. 14. GAREY JG, CHAN MM. Acceptance and Consumption of Reduced Sodium Hot Focal Items. Accepted for publication in School Foodservice Res. Rev. 1985; 9(1). 15. USDA. Nutritive Value of American Foods. Agricultural Handbook No. 456. Washington DC: US Govt Printing Office, 1975. 16. MATTES RD, KUMANYIKA SK, HALPERN BP. Salt Taste Responsiveness and Preference Among Normotensive, Prehypertensive and Hypertensive Adults. Chemical Senses 1983; 8: 27-40.

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17. CHAMBERS JM, CLEVELAND WS, KLEINER B, TUKEY PA. Graphical Methods for Data Analysis. Belmont CA: Wadsworth Inc., 1983. 18. BECKER RA, CHAMBERS JM. S: An Interactive Environment for Data Analysis and Graphics. Belmont CA: Wadsworth Inc., 1984. 19. BLAIS C, PANGBORN RM, FERRELL MF, BORHANI NO. Effect of Dietary Sodium Restriction on Taste Perception of Sodium Chloride in Salted Soups: Preliminary Results. Abstract presented at the VI AChemS conference at Sarasota, FL, 1984. 20. McCARRON DA, MORRIS CD, COLE, C. Dietary Calcium in Human Hypertension. Science 1982; 217: 267-69.

Accepted for publication September 30, 1985.