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ORIGINAL ARTICLE
Year : 2021  |  Volume : 11  |  Issue : 4  |  Page : 287-292

Influence of Abdominal Obesity (Waist–Hip ratio) on Memory Consolidation in Adolescent Medical Undergraduates − A Cross-sectional Study


1 CRRI, Saveetha Medical College, Thandalam, Chennai, Tamil Nadu, India
2 Department of Physiology, Saveetha Medical College, Thandalam, Chennai, Tamil Nadu, India

Date of Submission28-Jun-2021
Date of Decision14-Jul-2021
Date of Acceptance27-Jul-2021
Date of Web Publication26-Oct-2021

Correspondence Address:
Prathibha K Muthu
Department of Physiology, Saveetha Medical College, Thandalam, Chennai 602105, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijnpnd.ijnpnd_51_21

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   Abstract 


Background: Waist Hip Ratio (WHR), a measure of abdominal obesity is being co-related with memory consolidation based on its relation with stress and sleep. The objective of the present cross-sectional study was to evaluate the association between WHR and memory consolidation in adolescent medical undergraduates. Methodology: An analytical cross-sectional study was conducted in a South Indian medical college. After obtaining ethics clearance, the study was conducted on 42 males and 63 females of 17–19 years of age. WHR was measured according to WHO guidelines using Gulick 2 plus inch tape. Sleep-dependent memory consolidation test was conducted in evening 3:00 pm followed by next morning 9:00 am. WHR between genders was compared using Student t test. The study population was divided into obese and non obese individuals, based on the calculated WHR. Then, the mean memory consolidation test scores were compared using Mann Whitney U test. The correlation between WHR and memory consolidation test scores was evaluated using Pearson’s correlation test. Results & Discussion: The average WHR of males (0.845 ± 0.058) was significantly higher than females (0.778 ± 0.051) (P<0.001). The morning session memory consolidation test scores were higher in the normal group when compared to the substantially increased risk for obesity groups, although not statistically significant. WHR showed significant negative correlation with sleep dependent memory experiment scores. Conclusion: The relationship between WHR and memory consolidation in the present study highlights the need for an awareness to adopt life style modifications which might not only benefit the general health status but also might have an impact on their memory consolidation and academic performance.

Keywords: Abdominal obesity, memory consolidation, metabolic syndrome, obesity, stress, WHR


How to cite this article:
Rakesh R, Muthu PK, Sundararajan PK, Gutta NK. Influence of Abdominal Obesity (Waist–Hip ratio) on Memory Consolidation in Adolescent Medical Undergraduates − A Cross-sectional Study. Int J Nutr Pharmacol Neurol Dis 2021;11:287-92

How to cite this URL:
Rakesh R, Muthu PK, Sundararajan PK, Gutta NK. Influence of Abdominal Obesity (Waist–Hip ratio) on Memory Consolidation in Adolescent Medical Undergraduates − A Cross-sectional Study. Int J Nutr Pharmacol Neurol Dis [serial online] 2021 [cited 2021 Dec 3];11:287-92. Available from: https://www.ijnpnd.com/text.asp?2021/11/4/287/329203




   Introduction Top


Stress is a process in which environmental or psychologic events, called stressors, threaten an organism’s safety and well-being.[1] Stress and anxiety cause activation of the sympathetic nervous system and not only induces hypertension but also has an influence on the endocrine system which is hypersensitive to the hypothalamic pituitary adrenal axis.[2],[3],[4] Wardle et al. reported that cortisol is associated with higher levels of abdominal fat and therefore, a higher waist–hip ratio (WHR).[5] In addition, stress and the associated inhibition of sex steroids and growth-hormone secretion cause central, visceral, and adipose tissue depots.[4],[6] Abdominal fat is a marker of visceral fat and has greater blood flow and more receptors for cortisol than peripheral fat. The greater the number of cortisol receptors, the more sensitive the visceral fat tissue is to cortisol. This heightened sensitivity to cortisol stimulates fat cells to further increase in size.[7]

The WHR or the ratio of waist circumference (WC) and hip circumference (HC) is a sexually dimorphic trait with females showing lower ratios when compared with males. The circulating estrogen preferentially stores lipid deposits in the gluteofemoral region, including the buttocks and thighs. Existing evidence suggested that menopause-associated estrogen deficiency resulted in an accumulation of adipose deposits around the abdomen.[8] The World Health Organization (WHO) defines abdominal obesity as a WHR above 0.90 for males and 0.85 for females.[9] According to The National Institute of Diabetes, Digestive, and Kidney Diseases, women with WHR above 0.8 and men above 1.0 are considered to be at health risks because of fat distribution.[9]

Restricted sleep is a widespread and serious problem in the present days.[10],[11] Stress is perhaps one of the most common precipitants of sleep disturbances; yet only a few studies have systematically examined its relationship to insomnia.[12],[13],[14] Healey et al. reported a significant relationship between major stressful events and the onset of insomnia.[14] Rubman et al. found that daily minor stressors correlated with more sleep disturbances among insomnia sufferers.[15] Sleep plays an important role in maintenance and stabilization of declarative memory, enhancement of procedural memory, including visual and motor skill learning, and memory consolidation.[16],[17],[18]

Sleep deprivation was also reported to cause excessive fatigue which in turn might lead to reduced physical activity and obesity.[19],[20] In addition, sleep disturbances are also proven to cause neuro-hormonal effects that increase the caloric intake and thereby, result in abdominal obesity.[21] Various studies have also explored the relationship between stress and sleep disturbances on memory consolidation. Among adolescent males and females (below 20 years of age) in India, it was reported that 4% to 6% of adolescents were overweight, whereas 1.5% to 3% belonged to the obese categories.[22] In addition, the proportion of children and adolescents with a body mass index of 25 or greater was 12.9% (12.3–13.5%) for boys and 13.4% (13.0–13.9%) for girls.[22] The authors of the present study wished to propose the hypothesis linking stress, sleep disturbances, energy metabolism, abdominal obesity, and memory consolidation [Figure 1].
Figure 1 Flow chart of the hypothesis linking stress, sleep disturbances, energy metabolism, abdominal obesity, and memory consolidation.

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The objectives of the present study were to compare the WHR and memory consolidation test scores between males and females of 18 to 19 years age group, to compare the memory consolidation scores between normal and substantially increased risk for obesity groups in the study participants and correlate the WHR of normal and substantially increased risk for obesity groups with their memory consolidation test scores.


   Materials and Methods Top


Ethical considerations

The study was initiated after presentation of the proposal to and obtaining clearance from the Institutional Review Board of Saveetha Medical College and Hospital (SMC/1RB/185). Information sheet with pertinent information was given to all the participants invited to participate in the study. Written informed consent was obtained from all participants of the study.

Study setting and population

The present analytical cross-sectional study was conducted on the adolescents of 18 to 19 years of age pursuing medicine at Saveetha University. Based on existing literature, the estimated sample size was calculated to be 105 participants (42 males and 63 females).[23] The sampling frame comprised of the list of all eligible students of 18 to 19 years pursuing medicine in Saveetha Medical College. A total of 110 students were selected using computer-generated random numbers. The inclusion criteria comprised of adolescents of 18 to 19 years age group willing to participate in the study. Participants with any history of injury/surgeries/congenital abnormalities in the waist and/or hip or those suffering from diarrhea or constipation were excluded from the study.

Procedure

After obtaining written informed consent from study participants, the basic demographic details (age, sex, year, and course of study) were collected. WC and HC measurements were carried out according to the WHO’s data gathering protocol using Gulick 2 plus tape. WC was measured at the midpoint between the lower margin of the last palpable rib and the top of the iliac crest, using a stretch resistant tape that provides a constant 100-g tension.[24] HC was measured around the widest portion of the buttocks, with the tape parallel to the floor [Figure 1].[9] For both the measurements, the individual was made to stand with feet close together, arms at the side and body weight evenly distributed. The subject was allowed to be relaxed and the measurements were taken at the end of a normal expiration. Each measurement was repeated twice; if the measurements were within 1 cm of one another, the average was calculated. If the difference between the two measurements exceeded 1 cm, the two measurements were repeated.[9]

Gulick tape is used for accurate body measurement and enables consistent user-independent measurement of waist, arms, legs, etc. It has a consistent tension of 6 oz. It has a spring-loaded, self-winding case which is very convenient to handle. It is measured using the side with English units from 0 to 60″. It is used for accurate body measurement and enables consistent user-independent measurement.

Administration of sleep-dependent memory experiment

Sleep-dependent memory experiment was used to measure the working memory capacity. It was a self-reported experiment containing two sessions to test memory consolidation.[25]

The two sessions were separated by 12 hours of retention. The first session was conducted at 3 pm on day 1. The activity sheet consisted of 48 word pairs. Each word pair was displayed for 4 seconds. After displaying all the word pairs for a training session, a test with 40 pairs was conducted immediately. The second session was conducted at morning 9 am of day 2 (18 hours after the first session on day 1). The same test with 40-word pairs was conducted. The test marks were dependent on the working memory capacity of the participant and was also a measure of the memory consolidation.

Statistical analysis

All data were entered into MS excel and checked for data entry errors. Statistical analysis was performed using SPSS 17.0 (IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp.). Descriptive data were presented as mean ± standard deviation for continuous variables and as proportions for qualitative variables. WHR between males and females among the study participants was compared using Student t test. Following the calculation of WHR, the study population was divided into obese and nonobese individuals, based on the WHO criteria. Then, the mean memory consolidation test scores between the obese and nonobese adolescent medical undergraduates were compared using Mann–Whitney U test. The correlation between WHR and memory consolidation test scores was evaluated using Pearson correlation test.


   Results Top


The total number of participants in the present study was 105, of which there were 42 males (40%) and 63 females (60%). [Table 1] summarizes the distribution of anthropometric measures, namely WC, HC, and WHR in the study population. The mean WC and HC of the study population were 74.2381 ± 11.037 cm and 92.043 ± 9.4105 cm, respectively. The average WHR of the study population was 0.99 ± 0.02.
Table 1 Distribution of anthropometric measures in study population (n = 105)

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The mean WC of males was higher than the females, whereas the mean HC was higher in females than males, although the differences were not statistically significant [Table 2]. The average WHR of males (0.845 ± 0.058) was significantly higher than females (0.778 ± 0.051; P < 0.001). Further, the study population was classified into two groups based on the standard WHR cutoff values − normal and substantially increased risk for obesity.[26] Using Chi-squared test, it was observed that there was no significant association between genders and WHR-risk subgroups (Chi statistic: 1.897, P = 0.168).
Table 2 Gender-wise distribution of anthropometric measures in study population (n = 105)

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The average score of the sleep-dependent memory experiment during the evening session (day 1–3 pm) and the morning session (day 2 at 9 am; 18 hours later) was 22.52 ± 9.618 and 28.25 ± 10.787, respectively. The mean difference in the scores between the morning and evening sessions was 5.76 ± 7.734. [Table 3] summarizes the proportions of participants based on the change in memory score between the morning and evening sessions. The percentage change from evening session scores ranged from −70% to 525%.
Table 3 Classification of study population based on percentage of change in scores from evening to morning sessions of memory consolidation test

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Further, [Table 4] summarizes the gender-wise comparison of the scores (using Student t test) in the study population, during both the evening and morning sessions. The females had significantly higher scores when compared with the males, in both the evening and morning sessions (P < 0.0001) [Table 4]. In addition, the difference in scores between the morning and evening sessions of the memory experiment was statistically significant (P < 0.0001).
Table 4 Gender-wise distribution of sleep-dependent memory experiment scores (evening and morning sessions) in study population

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As given in [Table 5], the evening session scores were similar between the normal and substantially increased risk for obesity groups. The morning session scores were higher in the normal group when compared with the substantially increased risk for obesity groups, although not statistically significant. In addition, the difference between the morning and evening session scores was similar (not significantly different) between the normal and substantially increased risk for obesity groups [Table 5]. The study participants who observed an increase in memory test scores had a lesser WHR when compared with those who had no/fall in scores, although there was no statistical significance.
Table 5 Comparison of evening and morning session scores across waist–hip ratio (WHR)-risk categories (normal and substantially increased risk)

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The WHR of the study participants showed a statistically significant negative correlation with sleep-dependent memory experiment scores (P = 0.001 for evening session scores and P = 0.000 for morning scores) [Table 6]. As the WHR decreased, the scores of the sleep-dependent memory experiment increased.
Table 6 Correlation between waist–hip ratio (WHR) and sleep-dependent memory experiment scores

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   Discussion Top


Extensive literature review revealed that the stress hormone, cortisol, was associated with higher levels of abdominal fat and therefore, a higher WHR.[5] Stress is one of the most common precipitants of sleep disturbances and many studies have systematically examined its relationship to insomnia.[12],[13],[14] Further, it is a well-known fact that sleep induces memory consolidation.[18] In the present study, the authors explored the obesity–memory consolidation link and planned to study the relationship between WHR (as a marker of abdominal obesity) and memory consolidation.

The cutoff of WHR ≥0.90 in males and ≥0.85 in females was used to indicate the substantially increased risk for development of metabolic complications. Based on the above-mentioned cutoff, the proportions of males and females at substantially increased risk of developing metabolic complications in the present study were calculated to be 7.9% and 16.7%, respectively. In a large study conducted on 10,025 Asian Indians adults of age below 20 years, the cutoff values for WC were taken to be 85 and 80 cm for men and women, respectively, and the corresponding WHR cutoffs were 0.88 and 0.81, respectively.[27] A substantial number of North Indian adolescents in the general population (4.2%) and 36.6% of overweight adolescents, especially had metabolic syndrome in the study conducted by Snehalatha et al.[28] In another cross-sectional study, conducted in public schools of Delhi, the prevalence of obesity and overweight was 5.3% and 15.2%, respectively.[29]

In the present study, the mean WC of males was higher than the females, whereas the mean HC was higher in females than males. The results of the present study were concurrent with those of the Spanish population, studied by Witte et al., who reported that WC tended to be higher in males than in females and this difference was significant even when measured after a decade. Further, the study also reported that the HC was higher in females than in males.[30] The average WHR of males (0.845 ± 0.058) was significantly higher than females (0.778 ± 0.051; P < 0.001). The average values were slightly lower than the Asian standards. The values of the present study were similar to the reports of a study conducted on urban South Indian adolescents in Bangalore.[31]

The average scores of the sleep-dependent memory experiment for evening session and morning session were 22.52 ± 9.618 and 28.25 ± 10.787, respectively. The mean difference in the scores between the morning and evening sessions was 5.76 ± 7.734. In a similar study conducted by Fenn and Hambrick, the group that was tested after sleep showed a significant improvement in recall performance, whereas the wake group did not.[25] The above finding was consistent with the results of the present study and this could be attributed to the fact that consolidation during sleep improved declarative memory performance. The percentage of change from evening to morning session in scores ranged from −70% to 525%. In the earlier study mentioned, the amount of change ranged from a loss of 42% to a gain of 37% in the wake group and from a loss of 3% to a gain of 44% in the sleep group, indicating a better performance in the sleep group.

The study participants who observed an increase in memory test scores had a lesser WHR when compared with those who had no/fall in scores. In addition, the two key findings of the present study were that females had higher scores in both evening and morning sessions and that the morning session scores were higher in the normal group when compared with the substantially increased risk for obesity groups, although not statistically significant. In a study by Heyward et al., a significant increase in verbal memory scores was observed in adult females who underwent caloric restriction and it was also correlated with decreases in fasting plasma levels of insulin and high sensitive C-reactive protein.[32]

In the present study, the WHR of the study participants showed a statistically significant negative correlation with sleep-dependent memory experiment scores. As the WHR decreased, the scores of the sleep-dependent memory experiment increased. Heyward et al. suggested that obese animals presented with memory impairment. Aberrant gene expression within the hippocampus was implicated in the pathogenesis of obesity-induced memory impairment with the evidence of obesity-induced alterations in DNA methylation of memory-associated genes, including Sirtuin 1 (Sirt1), within the hippocampus.[32] Forebrain neuron-specific Sirt1 knock-out mice mimicked the memory deficits exhibited by obese mice, consistent with the hypothesis that the high-fat diet-mediated reduction of hippocampal SIRT1 could be responsible for obesity-linked memory impairment. In another study, obese mice that were fed on a diet supplemented with the SIRT1-activating molecule, resveratrol exhibited increased hippocampal SIRT1 activity and preserved the hippocampus-dependent memory.[33]

A larger sample size and modified timings (6 pm for evening session and 6 am for morning session) could have yielded more precise results. The college timings and availability of students posed a limitation to the conduct of the sessions. In addition, dropouts after the evening session contributed to further fall in sample size of the study.


   Conclusion Top


Establishing a relationship between WHR and memory consolidation might help to create an awareness to adopt lifestyle modifications which might not only benefit the general health status but also might have an impact on their memory consolidation and academic performance. The present study motivated us to further understand specific links between obesity, probably induced by stress, excessive screen time with gadgets or sleep disturbances, and its impact on memory consolidation. Future research on a larger sample size with objective monitoring of the sleep patterns of the study participants, prior to the morning session could help the investigators to identify more significant relationships between obesity and memory consolidation. More studies should be aimed at establishing the scientific understanding of mechanisms underlying both online and offline memory processing and their relationship to the metabolic processes contributing to obesity induced by stress and sleep disturbances.

Financial support and sponsorship

This study was funded by ICMR STS Funding (2016-00594).

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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