Abstract
Background: Sugar is routinely used to comfort neonates undergoing painful procedures, and animal studies have shown that sucrose increases the time to withdrawal from painful stimuli. However, there are no published studies examining the effects of sweet substances on heat pain thresholds and percept in adult humans. Methods: Healthy adult volunteers (n=27, aged 18-48 years) were recruited to a controlled, double-blind, randomised, cross-over study to characterise the effect of tasting solutions of equivalent sweetness (10% sucrose and 0.016% sucralose) on warm detection and heat pain thresholds and the percept ratings of painfully hot stimuli. The effect of anticipation of a sweet taste on heat pain threshold was also assessed. Results: Tasting either sucrose or sucralose had no significant effect on the percept of an individually titrated hot stimulus (54.5±4.2 and 54.9±3.2 vs 53.2±3.5 for water, 0-100 visual analogue scale), on the warm detection or heat pain threshold (43.3±0.8, 43.2±0.8 vs 43.0±0.8°C). Anticipation of a sweet substance similarly did not affect heat pain thresholds. Conclusions: Sucrose and sucralose solutions had no analgesic effect when assessed using heat detection thresholds and percept ratings of painfully hot stimuli despite being perceived as sweeter and more pleasant than water. These findings are in contrast to results reported from previous animal studies in which thermal analgesia from sweet solutions is robust. Given the ubiquitous availability of sugar rich drinks in the modern environment, the lack of observable effect may be due to an insufficient hedonic value of the test solutions when compared to the experience of a laboratory rodent. Alternatively, sweet tastes may have a specific effect on pain tolerance rather than the threshold and acute percept measures assayed in this study.
Highlights
It is commonly observed that humans who are in pain, discomfort or have a negative emotional state seek solace in the form of sweet foods and drinks
A previous study in humans demonstrated an analgesic effect of sweet solutions only in those who preferred high concentration sweet solutions[6]
To assess whether there was a population of participants who had a preference for less sweet solutions, participants rated the sweetness and pleasantness of weaker solutions of 5% sucrose and 0.008% sucralose. 5% sucrose was rated to be significantly less sweet than 10% sucrose but the difference in sweetness rating between 0.016% and 0.008% sucralose did not reach significance
Summary
It is commonly observed that humans who are in pain, discomfort or have a negative emotional state seek solace in the form of sweet foods and drinks. A recent study has demonstrated that active consumption of sucrose produces an analgesic effect in adult rats[5], slowing withdrawal from a painful thermal stimulus. Conclusions: Sucrose and sucralose solutions had no analgesic effect when assessed using heat detection thresholds and percept ratings of painfully hot stimuli despite being perceived as sweeter and more pleasant than water. These findings are in contrast to results reported from previous animal studies in which thermal analgesia from sweet solutions is robust. Sweet tastes may have a specific effect on pain tolerance rather than the threshold and acute percept measures assayed in this study
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