The influence of food on pain perception in healthy human volunteers

The Effect of Praying on Endogenous Pain Modulation and Pain Intensity in Healthy Religious Individuals in Lebanon: A Randomized Controlled Trial

Prayer is considered to be the most common therapy used in alternative medicine. This study aimed to explore the effect of prayers on endogenous pain modulation, pain intensity, and sensitivity in healthy religious participants. A total of 208 healthy religious participants were enrolled in this study and randomly distributed into two groups, a prayer group (n = 156) and a poem reading or control group (n = 52). Participants from the prayer group were then selectively allocated using the prayer function scale to either an active prayer group (n = 94) receiving an active type of praying or to a passive prayer group (n = 62) receiving a passive type of praying. Pain assessments were performed before and following the interventions and included pressure pain threshold assessment (PPT), conditioned pain modulation (CPM), and a numerical pain rating scale. A significant group-by-time interaction for PPT (p = 0.014) indicated post-intervention increases in PPT in the prayer group but not in the poem reading control group. Participants experienced a decrease in CPM efficacy (p = 0.030) and a reduction in their NPRS (p < 0.001) following the interventions, independent of their group allocation. The results showed that prayer, irrespective of the type, can positively affect pain sensitivity and intensity, but does not influence endogenous pain inhibition during hot water immersion. Future research should focus on understanding the mechanism behind "prayer-induced analgesia."

Effects of repeated exposures to experimental cold pain stimulus on pain perception in healthy young Indian men

Background

The influence of repeated exposures to cold pain stimulus, a surrogate of clinical pain, has remained largely unexplored. The study was planned to test the effect of repeated exposures to cold pain through cold pressor task on pain sensitivity and vascular reactivity.

Methods

Single-group experimental study. Thirty-seven healthy male volunteers (18-25 years) were exposed to cold pressor tasks for seven consecutive days and on the 14th day on the nondominant hand. The same was repeated on dominant hand on first and seventh days; 31 completed the protocol.

Results

Pain threshold and tolerance in the nondominant hand increased from day 1 to day 7 (p < 0.001) and were positively correlated on day 1 ( ρ =0.45, p = 0.011) and day 7 ( ρ =0.38, p = 0.036). Diastolic blood pressure response was found to increase by day 7 (p < 0.0024) and positively correlated with tolerance. On the dominant hand, the threshold reduced from day 1 to day 7, while tolerance increased. Both threshold and tolerance remained lower than that of nondominant hand. Day 14 values of threshold and tolerance were in between day 1 and day 7 values but not significantly different from both.

Conclusion

Habituation in pain threshold and tolerance was observed on repeated exposure to cold pain, which was not significantly retained till the 14th day. The same was not observed with subjective feeling of pain perception. The increased diastolic blood pressure response is suggestive of peripheral vasoconstriction. Increased tolerance in the dominant hand by day 7 demonstrates a systemic effect in habituation.

Involvement of cannabinoid type 1 receptor in fasting-induced analgesia

The endocannabinoid system (ECS) is known to modulate not only food intake but also pain, especially via the cannabinoid type 1 receptor (CB1R) expressed throughout the central nervous system and the peripheral tissues. Our previous study demonstrated that fasting produces an analgesic effect in adult male mice, which is reversed by intraperitoneal (i.p.) administration of CB1R antagonist (SR 141716). In the present study, we further examined the effect of CB1R expressed in the peripheral tissues. In the formalin-induced inflammatory pain model, i.p. administration of peripherally restricted CB1R antagonist (AM 6545) reversed fasting-induced analgesia. However, intraplantar administration of SR 141716 did not affect fasting-induced analgesia. Furthermore, mRNA expression of CB1R did not change in the formalin model by fasting in the dorsal root ganglia. The formalin-induced c-Fos expression at the spinal cord level was not affected by fasting, and in vivo recording from the superficial dorsal horn of the lumbar spinal cord revealed that fasting did not affect formalin-induced neural activity, which indicates minimal involvement of the spinal cord in fasting-induced analgesia. Finally, when we performed subdiaphragmatic vagotomy to block the hunger signal from the gastrointestinal (GI) system, AM 6545 did not affect fasting-induced analgesia, but SR 141716 still reversed fasting-induced analgesia. Taken together, our results suggest that both peripheral and central CB1Rs contribute to fasting-induced analgesic effects and the CB1Rs in the GI system which transmit fasting signals to the brain, rather than those in the peripheral sensory neurons, may contribute to fasting-induced analgesic effects.

The analgesic effect of refeeding on acute and chronic inflammatory pain

Pain is susceptible to various cognitive factors. Suppression of pain by hunger is well known, but the effect of food intake after fasting (i.e. refeeding) on pain remains unknown. In the present study, we examined whether inflammatory pain behavior is affected by 24 h fasting and 2 h refeeding. In formalin-induced acute inflammatory pain model, fasting suppressed pain behavior only in the second phase and the analgesic effect was also observed after refeeding. Furthermore, in Complete Freund’s adjuvant-induced chronic inflammatory pain model, both fasting and refeeding reduced spontaneous pain response. Refeeding with non-calorie agar produced an analgesic effect. Besides, intraperitoneal (i.p.) administration of glucose after fasting, which mimics calorie recovery following refeeding, induced analgesic effect. Administration of opioid receptor antagonist (naloxone, i.p.) and cannabinoid receptor antagonist (SR 141716, i.p.) reversed fasting-induced analgesia, but did not affect refeeding-induced analgesia in acute inflammatory pain model. Taken together, our results show that refeeding produce analgesia in inflammatory pain condition, which is associated with eating behavior and calorie recovery effect.

Heightened eating drive and visual food stimuli attenuate central nociceptive processing

Hunger and pain are basic drives that compete for a behavioral response when experienced together. To investigate the cortical processes underlying hunger-pain interactions, we manipulated participants' hunger and presented photographs of appetizing food or inedible objects in combination with painful laser stimuli. Fourteen healthy participants completed two EEG sessions: one after an overnight fast, the other following a large breakfast. Spatio-temporal patterns of cortical activation underlying the hunger-pain competition were explored with 128-channel EEG recordings and source dipole analysis of laser-evoked potentials (LEPs). We found that initial pain ratings were temporarily reduced when participants were hungry compared with fed. Source activity in parahippocampal gyrus was weaker when participants were hungry, and activations of operculo-insular cortex, anterior cingulate cortex, parahippocampal gyrus, and cerebellum were smaller in the context of appetitive food photographs than in that of inedible object photographs. Cortical processing of noxious stimuli in pain-related brain structures is reduced and pain temporarily attenuated when people are hungry or passively viewing food photographs, suggesting a possible interaction between the opposing motivational forces of the eating drive and pain.

The relationship between pain and eating among overweight and obese individuals with osteoarthritis: an ecological momentary study

The relationship between pain and overweight/obesity is bidirectional – excess weight can cause pain, yet eating food high in calories, fat and sugar has been shown to alleviate pain. It appears likely that overweight/obese individuals may turn to these types of foods when they experience pain, leading to weight gain; however, this phenomenon has not been examined to date. The authors of this study set out to elucidate the relationship between pain and food intake in obese and overweight patients with osteoarthritis.

BACKGROUND:

Osteoarthritis (OA) patients who are overweight or obese report higher levels of pain compared with their normal-weight OA counterparts. Evidence suggests that overweight or obese OA patients also experience pain relief from eating foods high in calories, fat or sugar. Eating to alleviate pain may be problematic because it can lead to additional weight gain, which may contribute to heightened pain.

OBJECTIVES:

To investigate the relationship between pain and food intake using ecological momentary assessments in a sample of 71 over-weight and obese OA patients.

METHODS:

Participants completed two consecutive days of diary entries in which they recorded their levels of pain, mood and food intake throughout the day. Data were analyzed using generalized estimating equations that modelled pain as a predictor of calorie, fat and sugar intake. All models were adjusted for sex, body mass index, negative mood, time and treatment history.

RESULTS:

Pain significantly predicted calorie (Z=2.57; P=0.01) and fat intake (Z=1.99; P=0.05).

CONCLUSIONS:

Using ecological momentary assessments as a novel approach, the present study provides preliminary data supporting a relationship between pain and food intake among overweight and obese OA patients. Continued advances in our understanding of the relationship between pain and eating behaviour may help to optimize intervention strategies for these patients.

Intact sensory function in anorexia nervosa

BACKGROUND

In anorexia nervosa (AN), taste and smell are believed to be anhedonic, hunger and pain are muted, and body-image distortion obscures wasting, which together facilitate self-starvation. However, the emphasis on these deficits may be biased because other sensory systems have been sparsely investigated.

OBJECTIVES

Objectives of the study were to clarify whether these dysfunctions are specific or part of a pattern of sensory-perceptual deficits in AN patients and to test the gustatory senses dissociated from ingestion to clarify whether any deficit is sensory or affective.

DESIGN

In 15 adolescent, first-episode, hospitalized, restrictive AN patients and 15 matched healthy controls who responded to gustatory stimuli (intensity and hedonics of 5 basic tastes and tastes and odors of foods and nonfoods), size estimation (manual and oral judgment of size and shape, kinesthesia, and body size and esthetics), cold pain, and auditory and visual processing were compared.

RESULTS

AN patients did not differ on most tests, were better at odor recognition, were less successful in central auditory processing and oral assessment of size and shape, and may have been more sensitive to cold. Body-image dissatisfaction in AN patients was not related to dysfunctional size estimation.

CONCLUSIONS

There is no systematic sensory-perceptual deficit in AN patients, and specifically, not in gustatory function. The few differences shown might be due to fear of food-related stimuli or comorbidity.

Abuse liability of oxycodone as a function of pain and drug use history

The relationship between pain and prescription opioid abuse is poorly understood. Determining whether a patient is seeking additional opioid medications in order to alleviate pain or to abuse the drugs can be difficult. The present study was designed to evaluate two variables that may influence the abuse liability of opioids: drug use history and the presence or absence of experimentally induced pain. Eighteen healthy participants completed this outpatient study. One group was abusing prescription opioids (N=9) and one group had used prescription opioids medically but did not abuse them (N=9). All participants completed twelve sessions during which the effects of orally delivered oxycodone (0, 15, 30mg/70kg, PO) were examined. One dose was tested per day under double-blind conditions and sessions were separated by at least 48h. During the first "sample" session each week, participants were given $10 and the dose that was available later that week. During the second "choice" session, participants could self-administer either money or the previously sampled dose. Six sessions involved repeated hand immersions in cold water (4 degrees C) and six sessions involved immersions in warm water (37 degrees C). Most of the positive subjective effects of oxycodone were similar between the groups, but oxycodone self-administration significantly differed between groups. Non-abusers self-administered active doses of oxycodone only when they were in pain while abusers self-administered oxycodone regardless of the pain condition. These data suggest that an assessment of the reinforcing effects of opioids may be a sensitive method for differentiating opioid abusers from non-abusers.

Smoking status and pain level among head and neck cancer patients

Smoking is a risk factor for cancer of the upper aerodigestive tract with recidivism rates high even after diagnosis. Nicotine, a major product in tobacco, is a complex drug with multiple characteristics including analgesic properties. The goal of the study was to examine pain levels in the context of smoking status among patients recently diagnosed with cancer of the upper aerodigestive tract who have not yet received any treatment including radiation, surgery, or chemotherapy. A convenience sample of 112 newly diagnosed head and neck cancer patients (78 men and 34 women) was recruited from clinics at the University of Florida. Smoking rates were: 32% never smoked, 34% former smokers, 34% current smokers. Among current smokers, 62% reported plans to quit in the next 3 months and 38% had tried to quit more than 3 times in the past 5 years. Current smokers reported higher general (sensory and affective) and oral pain levels (spontaneous and functional) and pain-related interference than did never and former smokers (all F's > 8. and P's < .0001) even after controlling for stage of diagnosis. In addition, current smokers reported significantly greater interference from the pain (F(2,73) = 10.5 P < .0001).

PERSPECTIVE

This study highlights the importance of understanding self-reported pain in cancer patients who continue to smoke. When pain is elevated, smokers may be motivated to use tobacco as a means of reducing pain, which in turn reinforces smoking behavior. Tobacco cessation programs should include pain management as a component of treatment.

Metallic taste phantom predicts oral pain among 5-year survivors of head and neck cancer

Chronic pain following cancer-related treatment is emerging as a major concern. Heretofore, the pain level among 5-year survivors of head and neck cancer has received limited attention. This study proposes a predictive model for understanding factors associated with the elevated levels of chronic oral pain. Cancer survivors were drawn from a pool of 5-year survivors. A listed sample matched on sex, age, and zip code was purchased and served as a comparison group. Telephone interviews were conducted by a professional call center. Oral pain levels and the presence of metallic taste phantoms were significantly higher in the cancer survivor group than among the comparison group. The prevalence of chronic oral pain among the 5-year survivors was 43% compared to 13% for the comparison group. Hierarchical linear regression showed that among the 5-year survivors, the predictive model for spontaneous pain accounted for 24% of the variance, and for function-related pain the model accounted for 34% of the variance, with the presence of a phantom metallic taste making a significant independent contribution in both models. In the function-related pain model, depression and level of oral function quality of life (QOL) made significant independent contributions. The presence of oral pain is a significant problem among head and neck cancer survivors. The presence of metallic phantoms is an important new piece of evidence suggesting neural damage following cancer-directed treatment. Routine assessment of oral pain levels could improve current analgesic approaches among head and neck cancer survivors.

Sweet taste and blood pressure-related analgesia

To test the prediction that sweet taste modifies responses to cold induced pain, 72 young adults held sweet, bitter and water solutions in their mouths, in counterbalanced order, before and during a cold pain stimulus. To test whether or not blood pressure interacts with sweet taste analgesia, measurements of resting blood pressure were also obtained. A significant main effect of taste on pain tolerance was observed, as well as a significant interaction between resting mean arterial pressure (MAP) and taste on tolerance. Sweet taste was associated with a prolongation of tolerance compared to the bitter and water conditions. When participants were split along the median for MAP, sweet taste was associated with an 18.1% increase in pain tolerance compared with water for those with lower MAP. No significant impact of taste on pain sensitivity was observed among participants with higher MAP. Groupwise comparisons revealed a significant difference in pain tolerance between participants with higher and lower MAP in the water condition but not in the sweet condition, replicating previous findings of a reduced sensitivity to pain among those with higher blood pressure. The analgesic effects of sweet tasting solutions seen previously in human infants and children may also be present in adults. Individuals with higher blood pressure may not be as sensitive to the presumably opioid-mediated analgesic effects of sweet taste, perhaps due to opioid dysregulation.

Modification of small bowel mechanosensitivity by intestinal fat

BACKGROUND

Lipids may exacerbate symptoms induced by gut stimuli.

AIM

To determine the mechanism whereby fat exerts this effect.

SUBJECTS

Twenty four healthy subjects were studied during fasting.

METHODS

We measured perception (0-6 scale) in response to jejunal balloon distension and transmucosal electrical nerve stimulation; phasic stimuli (one minute) were randomly applied at five minute intervals during intestinal infusion (2 ml/min) of saline and then Intralipid 2 kcal/min (high fat; n=8 subjects), Intralipid 0.5 kcal/min (low fat; n=8), or saline (n=8).

RESULTS

Intestinal lipids increased the perception of jejunal distension regardless of concentration (by 53% with high fat, 49% with low fat, and 17% with saline; p<0.05 for both fat loads). This effect could not be attributed to changes in intestinal compliance as intraballoon pressures remained unchanged during lipid infusion (2% change; NS). Sensitisation induced by lipids seemed to be specifically related to intestinal mechanoreceptors because electrical stimulation, which non-specifically activates gut afferents, was perceived equally during saline and lipid administration (10%, 11%, and 15% change during high fat, low fat, and saline, respectively; NS).

CONCLUSION

Physiological amounts of lipids heighten intestinal sensitivity by modulating intestinal mechanoreceptor response.

Relationship between increasing duodenal lipid doses, gastric perception, and plasma hormone levels in humans

Duodenal lipid causes gastric relaxation, CCK secretion, and nausea. Vasopressin has been implicated in motion sickness-related nausea. We hypothesized that increasing doses of lipid enhance gastric relaxation and CCK-vasopressin secretion, resulting in a dose-related exacerbation of nausea. Nine healthy subjects received isotonic saline or lipid (1, 2, or 3 kcal/min, L1, L2, L3) duodenally. Changes in gastric volume, sensations, and plasma hormone levels were assessed during infusions and isobaric gastric distensions. Lipid infusions increased gastric volume, plasma CCK (but not vasopressin) levels, and gastric compliance during distensions, compared with saline. Plasma CCK levels were related to the dose of lipid administered [CCK levels at 30 min (pmol/l), saline: 1.1 +/- 0.2, L1: 1.8 +/- 0.2, L2: 3.0 +/- 0.2, L3: 4.3 +/- 0.6]. During distensions, nausea increased in intensity with increasing doses of lipid [score (where 0 is no sensation and 100 is strongest sensation), saline: 7 +/- 4, L1: 19 +/- 7, L2: 44 +/- 7, L3: 66 +/- 8]; however, no further rise in plasma CCK occurred. Because neither lipid nor distension alone induced significant nausea, we conclude that the interaction between these stimuli together with a modulation by CCK is responsible for the effects observed. Vasopressin is not involved in lipid- and distension-induced nausea.

Skin-to-skin contact is analgesic in healthy newborns

OBJECTIVES

To determine whether skin-to-skin contact between mothers and their newborns will reduce the pain experienced by the infant during heel lance.

DESIGN

A prospective, randomized, controlled trial.

SETTING

Boston Medical Center, Boston, Massachusetts.

PARTICIPANTS

A total of 30 newborn infants were studied.

INTERVENTIONS

Infants were assigned randomly to either being held by their mothers in whole body, skin-to-skin contact or to no intervention (swaddled in crib) during a standard heel lance procedure.

OUTCOME MEASURES

The effectiveness of the intervention was determined by comparing crying, grimacing, and heart rate differences between contact and control infants during and after blood collection.

RESULTS

Crying and grimacing were reduced by 82% and 65%, respectively, from control infant levels during the heel lance procedure. Heart rate also was reduced substantially by contact.

CONCLUSION

Skin-to-skin contact is a remarkably potent intervention against the pain experienced during heel stick in newborns.

Suppression of pain sensation caused by millimeter waves: a double-blinded, cross-over, prospective human volunteer study

We conducted a double-blinded, randomized, cross-over, prospective trial to evaluate the pain relief effect of millimeter waves (MW) under experimental conditions. The cold pressor test was used as a model of tonic aching pain. Twelve healthy male volunteers were exposed to an active medical MW generator and to a disabled sham generator with at least 24 h between exposures. Characteristics of continuous-wave electromagnetic output from the active generator were: wavelength 7.1 mm, incident power density 25 +/- 5 mW/cm2, and duration of exposure 30 min. MW produced a significant (P < 0.05) suppression of pain sensation, with an average 37.7% gain in pain tolerance and a 49.3% increase in pain sensitivity range (the latter being the difference between pain tolerance and pain threshold values). Of the 12 volunteers, 7 (58.3%) reacted to the active MW generator with an increased pain tolerance, and the individual reactions varied from 120% to 315% comparison with their own preexposure levels. MW therapy can potentially be used as a supplementary or alternative treatment for pain relief.

IMPLICATIONS

Pain management is still a significant medical problem. In a double-blinded, experimental setting, we confirmed that low-intensity millimeter wave therapy can reduce pain sensitivity in healthy human volunteers and can potentially be used as a supplementary or alternative treatment for pain relief.

An examination of the effects of isoenergetic intragastric infusions of pure macronutrients on cold pain perception in healthy human volunteers

Our previous study demonstrated that meals, particularly when rich in fat, significantly reduced the pain induced by the cold pressor stimulus in healthy human subjects. To determine the mechanisms involved, the aim of this study was to bypass the taste and cognitive component of food and to investigate the scope of these analgesic effects with direct intragastric infusion of pure macronutrients in a group of 16 healthy human volunteers (eight male and eight female) on the response to cold-induced pain. All subjects underwent the cold pressor test (CPT) on three occasions in a counterbalanced order: before and after intragastric intubation and infusion of isoenergetic fat (10% intralipid), carbohydrate (CHO-maltodextrin), and a control infusion of isotonic saline. All solutions were of equal volume and administered at room temperature. The CPT was carried out four times on each test day, once before intubation, and 0.5, 1.5, and 2.5 h after intragastric infusion. Radial pulse and blood pressure measurements and visual analogue scales of mood/emotional state were carried out before and after each CPT. There were no significant differences in pain scores between the three test conditions, suggesting that by bypassing the cognitive and taste component of eating, the trigger for any postingestive analgesic effects of food are lost.

Effects of carbohydrate and lipid on resting energy expenditure, heart rate, sleepiness, and mood

The effects of gastric infusions of fat and carbohydrate on physiological and psychological measures were compared using a within subject design in 9 healthy subjects (6 males). Each subject received isovolaemic rapid gastric infusions of sucrose solution (100% energy carbohydrate), lipid emulsion (100% energy fat, 20% Intralipid), and a non-nutrient control (0.9% saline) in a randomised order. Nutrient infusions were isoenergetic, containing one-third of an individual subject's estimated daily energy requirements (mean, 3227 kJ; range, 2479-3971 kJ). Measures of heart rate (HR), energy expenditure (EE), mood, and sleepiness were collected before the infusions and every 0.5 h for 3.5 h. Mean postingestive HR, EE, and satiation were significantly greater after the nutrient infusions than after the control. Sucrose induced a rapid increase in HR and EE, whereas lipid had a lesser and more delayed effect. Thirty minutes after the gastric infusions, HR and EE were significantly higher after the sucrose than after the lipid and saline. Hedonic tone was greater and tension lower after the saline and sucrose infusions than after the lipid infusion. From 3 to 3.5 h after ingestion, subjects felt significantly more sleepy after the lipid infusion than they did at these times after the saline infusion, and significantly more dreamy after the lipid infusion than they did after the sucrose infusion. In conclusion, the presence of lipid and sucrose in the intestine induces significant and differing physiological and psychological effects, which are independent of cognitive and orosensory influences.