Sweetness, one of the most preferred taste sensations, can be characterized by an array of distinct attributes—some of which can be measured from an early age. In young children, psychophysical studies can provide data relevant to two separate attributes of taste: sensitivity of the system to chemical stimuli and the hedonic valence of the sensation [1
]. Measures of sensitivity include taste detection thresholds, just noticeable differences, intensity judgments, and sensory adaptation, whereas measures of hedonics include estimates of pleasantness, liking, or relative preferences. Although sensitivity and hedonics reflect distinct features of the taste system, and this distinction is usually unambiguous, the terms are often used interchangeably, despite little or no evidence that they are directly associated with one another.
Using validated methods that assess the hedonics of the taste system by directly measuring the level of sweetness preferred in participants of varying ages, research has shown that children experience tastes differently than adults, particularly sweet tastes. Compared to adults, children most prefer significantly higher concentrations of nutritive sugars (e.g., sucrose and fructose) [2
] and low-calorie sweeteners (e.g., aspartame and sucralose) [2
] than adults. For the sweet taste of sucrose, the adult pattern emerges during mid-adolescence [3
To our knowledge, the research suggesting similar age-related changes, beginning in childhood, in the sensitivity of the taste system is limited [9
]. While there is a gradual and steady decline in the ability to detect sucrose (i.e., higher concentrations of sucrose are required) from the second to eighth decade [9
], it is unclear whether such declines begin in childhood [9
]. There is wide variation in sucrose taste detection thresholds among children [9
], and one study reported that 8- to 9-year-old boys had higher sucrose detection thresholds (meaning they were less sensitive) than adults [13
]. Such age-related changes in taste sensitivity have been attributed to children’s inability to complete the detection threshold tasks and their shorter attention span [9
]. However, if sucrose detection thresholds are indeed higher in children than in adults, one explanation why they prefer higher levels of sweet taste is that they are less sensitive to its taste.
In the present study, our objectives were twofold. First, we aimed to determine whether there are age-related changes in taste detection thresholds for sucrose, as there are for sweet taste preferences. Second, we aimed to determine the degree of association between sucrose taste detection thresholds and the most preferred sucrose concentrations, and whether such relationships change from childhood to adulthood. To address these aims, we used psychophysical tools that have been validated for use in pediatric populations (e.g., the NIH Toolbox) [5
], which allow us to directly measure them in children and not rely solely on maternal reports, and in the case of taste detection thresholds, used clinically [15
]. Using identical methods for all participants allowed us to directly compare both sweet taste sensitivity and sweet taste preference across age groups.
Age independently associated with taste detection thresholds and preferences for the sweet taste of sucrose. Children had higher sucrose taste detection thresholds, meaning they required higher concentrations of sucrose to detect a taste different from water, compared to adolescents, who in turn required higher concentrations than adults. As shown in Figure 1
b, this translates to children requiring a 40% more concentrated sucrose solution to detect a taste, compared to adults.
Children also preferred higher sucrose concentrations than adults, with the changeover occurring during adolescence. As shown in Figure 2
b, this translates to approximately 12 sugar cubes dissolved in 230 mL (8 ounces) of water for children but only 8 sugar cubes in the same volume of water for adults. In present times, a typical cola has a sugar concentration of 320 mM, which is similar to the most preferred sucrose concentration in adults.
While the finding that sweet taste preference changes during development is consistent with a large body of research [2
], the finding that children are less sensitive to the taste of sucrose than adolescents, who in turn are less sensitive than adults, is rather novel and extends prior research documenting age-related changes from late adolescence to adulthood [9
]. That both of these dimensions of sweet taste perception change during development may suggest that age-related differences in sweet taste sensitivity cause children to prefer higher sucrose concentrations; that is, a given sucrose concentration just does not taste as sweet to children as it does to adults. However, that children differed from adolescents in taste detection thresholds but not in sucrose preferences, and the lack of significant relationships between detection thresholds and preferences across age groups, suggests that was not the case. The true test of this hypothesis would be to analyze the relationship between detection and preference within the same individuals as they age.
While taste detection threshold for sucrose and the most preferred sucrose concentration significantly changed with age, there were no significant relationships between the two. When analyzing age groups separately or combined, the most preferred sucrose concentration did not significantly correlate with the lowest concentration of sucrose that the individual detected. These findings are consistent with the lack of relationship between taste detection thresholds and the most preferred concentration of salt in children and adolescents, in a study that used the same methods as the present study [25
]. Prior research, using different psychophysical methods to determine taste preferences, also found no relationship between preference and detection thresholds for sucrose in adults [24
] or in adolescents [12
]. For example, 11- to 15-year-olds who were categorized as high versus low sweet likers, based on their rank ordering by preference of Kool Aid™ solutions that varied in sucrose concentrations, did not differ in sucrose taste detection thresholds [12
Several explanations, not mutually exclusive, may explain age-related differences in sweet preference and sweet taste detection thresholds and the lack of a relationship between these two dimensions of sweet taste from childhood to adulthood: (1) children’s inability to understand the task or difficulty sustaining attention, (2) age-related changes during adolescence resulting from distinct ontogenetic trajectories, and/or (3) heightened preference for sweets in children and adolescents reflecting greater physiological needs.
First, the age-related differences in both taste detection and preferences may have been due to children’s inability to understand the task or difficulty sustaining attention. However, both psychophysical tools used in the present study eliminated the need for verbal responses and controlled for position bias, which allowed for the objective determination of whether the participant comprehended the task or responded at random. The ability of children and adolescents to comprehend and complete the preference task was similar to that of adults. Further, their most preferred sucrose concentrations were not higher than adults simply because they repeatedly choose the highest sucrose concentration (1050 mM, 36% weight/volume) offered. While the taste detection threshold task was relatively more difficult for the younger participants than for adults, both psychophysical tasks had inclusion criterion established a priori and recommended clinically [15
] and, thus, it is unlikely that the age-related changes are due to differences in task performance.
Second, age-related changes in sucrose preferences and detection thresholds that occur during adolescence may result from distinct ontogenetic trajectories with different underlying mechanisms. The appetite or preferences for sweet taste may be consequences of central changes in the activity and morphology of the brain reward system [26
]. Using the same psychophysical methods we used here to measure sucrose preference, we found that the binding potential of dopamine receptors in striatum, a brain area that encodes reward value, decreased with age and also predicted, independently of age, the most preferred sucrose concentration in healthy young adults [28
On the other hand, developmental changes in detection thresholds may be secondary to peripheral changes in the anatomy of the oral cavity and the composition of saliva. It has been hypothesized that, as the surface of the tongue increases with body weight and with larger surface in primates, there would be greater numbers of taste buds to elicit a greater signal, thus resulting in increased sensitivity [29
]. In addition, changes occur during adolescence in the protein content and protein activity of saliva [30
]. For example, the activity of salivary amylase, an enzyme that catalyzes the breakdown of starch into sugar as a first step in the digestion process, increases from undetectable in newborns to adult levels by adolescence [30
]. Whether there are also age-related changes in alpha-glucosidase digestive enzymes expressed in taste buds remains unknown, but if so, we hypothesize that such changes in these enzymes that contribute to taste cell responses to disaccharides [32
] could underlie age-related changes in sucrose detection thresholds.
Third, the heightened preference for sweets in children and adolescents may, in part, reflect greater energetic needs due to growth [3
]. In support of this hypothesis, the level of sweetness most preferred has been shown to be significantly related to the height of children and urinary levels of N-terminal telopeptide of type 1 collagen, a biomarker for bone resorption and growth [12
]. Remarkably, the developmental-related change in sweet taste preference is not unique to humans since it has been observed in other mammalian orders, such as rodents [34
The attraction that youth have for “sweetness” reflects their inborn biology. It is believed that evolutionary pressures shaped the taste of foods initially preferred and rejected. In an environment with limited nutrients and abundant poisonous plants, sensory systems evolved to detect and reject perceptions that specified potential poisons that taste bitter [35
] and to prefer perceptions that specify crucial nutrients such as the once rare carbohydrate (energy)-rich plants that taste sweet [29
Whether age-related changes in taste sensitivity have selective advantages remains speculative. Unlike sweet taste, where sensitivity increases from childhood to young adulthood, the reverse has been observed for some bitter substances, a taste signal for potential poisons. For some bitter agents, children are more sensitive in detecting taste (lower detection thresholds) than adults, with the changeover occurring in adolescence [36
]. Although we have shown that 0.6 M sucrose solution can suppress bitterness in a variety of taste mixtures in both children and adults [37
], it remains unknown whether the relatively lower sweet detection thresholds in children modulate the efficacy of sugars in masking bitterness, which in turn would increase the likelihood that they would detect toxins in foods that contain both bitter compounds and small amounts of sugars.
The present findings must be interpreted considering some limitations. First, the cross-sectional study design does not allow determination of causality. Second, the nature of this secondary data analysis resulted in a sample of adults, the majority of whom were women who had overweight or obesity. However, it is unlikely that the sex and BMI imbalance among the adult group were factors for a number of reasons. First, both sucrose detection thresholds and preferences were within the range of previously published work [2
]. Second, prior research found no differences in either measure between men and women [3
] or adults with normal weight and those with obesity [28
]. Third, the absence of dietary intake data precludes the evaluation of how age-related changes in dietary intake [43
] contribute to changes in taste sensitivity and preference for sweet tastes. Future longitudinal research to determine how dietary intake of added sweeteners (with or without calories) impacts these two dimensions of the sweet taste system over time is warranted.