Abstract: Medical students in Malaysia and globally were considered among the most exposure groups in the community to stress due to several sources. The most significant and severe sources of stress in medical students is an academic sources, includes a lot of exams/tests, lack of time and facilities for entertainment, stay in a hostel, high parental expectations and vastness of syllabus, in addition to emotional problems and others personal sources. Stress is a very important issue that leads to a worsening of health problems. Stress develops in the body and leads to oxidative stress which in turn leads to a disorder in the whole body. Oxidative stress may lead to abnormal haematological indices elevated white blood cells (WBCs) count. Oxidative stress can lead to massive destruction of red blood cells (RBCs). The brain and the gastrointestinal system (GI) are intimately connected as one system. The brain has a direct impact on the GI tract. A stressful brain can send signals to the gut, just as a troubled intestine can send signals to the brain. Therefore, stress can be the cause of block the breakdown and assimilation of food for energy and nutriment. This malabsorption can then lead to a reciprocal negative effect to the stress and can be another cause of anaemia through malabsorption minerals and vitamins that are to erythropoiesis. So, stress can be one of the leading causes of anaemia among medical students. Stress is a chronic epidemic in the most medical students and can directly affect how well body works. This review article discovers the effect of stress in medical students that can be effect on their studies and further create researcher’s interest to generate database that help to reduce stress response and bring about the empowerment of balanced life among Malaysian medical students besides the increasing level of health and academic performance.
INTRODUCTION
"Hans Selye" defined stress as the common features of a stereo typed reaction of the living organism to all stimuli which tend to disturb the dynamic homeostasis of psychological, biochemical and physiological processes1. Antecedent to Selye’s were the works of Hippocrates, Bernard and Cannon. Selye’s model of stress was essentially a bio-chemical concept2, he theorized that stress was a result of any non-specific demand made upon an organism. Stress is unavoidable in the life, any person can face it at home, school, work and in our social lives. It is a fact of life and without stress, life would be very boring but on the other hand, too much stress becomes distress, this can become a serious illness if it persists for a long time, especially if it is not treated properly. A person who feels undergoing an untreated stress, may develops psychiatric disorders and can lead to many physiological health problems3. Stress occurs when an individual perceives that environmental demands tax or exceed his or her adaptive capacity. Operationally, studies of stress focus either on the occurrence of environmental events that are consensual judged as taxing one’s capability to cope or on individual responses to issues that are indicative of this overload4. All global studies of stress have been focusing on environmental events causing stress5. Study of medicine has been associated with increased exposure of medical students to stress, more than other people in other educational and academic fields. The most important and severe causes of stress in medical students are a lot of exams/tests, lack of time and facilities for entertainment, staying in hostel, high parental expectations and vastness of syllabus, beside emotional problems and others personal sources6-8. Socioeconomic status, familial relationships are also producing stress besides daily hassles, exams and academic stress9. It has observed, a good social support minimizes the risk of stress10,11. Family income with less than 1000 RM has found to be likely more stress in bachelor’s degree’s students and has a strong association with the mental disorder12. Lower socioeconomic status is leading towards stress in students13. Students may face problems in their daily expenditure with lower family income that cause poor results. Therefore, medical students in Malaysia are expected to have a few physiological disorders because they have high levels of stress. The medical community needs to know the most prevalent physiological disorders and to confirmation their relationship to stress among medical students in Malaysia.
PREVALENCE OF STRESS AMONG MEDICAL STUDENTS IN MALAYSIA
Faculty of medicines, in Malaysian universities have been reported as a stressful environment, that often exerts a negative effect on the psychological health and consequently on the physical health of the students (Table 1). In a study to explore stress among medical students in Universiti Sains Malaysia (USM), for determining the prevalence, sources and pattern of stress and the factors affecting it, they used a cross-sectional study design utilizing validated questionnaires to evaluate stress levels and stressors among a total of 761 (72%) medical students as respondents in this study. The results concluded the prevalence of stress among the medical students to be 29.6%, reflecting the prevalence of stress among medical students in USM to be very high. Academic related problems were the major stressor among medical students. The academic year of study was the factor most significantly associated with medical student’s stress15. In another cross-sectional study, conducted in the faculty of medicine at some of local universities in Malaysia, all medical students were selected as respondents. They used an instrument similar to the General Health Questionnaire (GHQ12) to screen for symptoms of psychological stress. The prevalence of psychological stress among medical students was high in this study. As a total of 41.9% of the medical students were found to have psychological stress16. Through a cross-sectional study conducted at University Sultan Zainal Abidin (UniSZA), Malaysia, a total of 60 questionnaires were administered to the pre-clinical medical students at faculty of medicine, UniSZA. Study subjects were selected randomly. This study showed that, 47 (78.3%) students might be having stress related/associated problems, several stressful causes have been measured and the major cause of stress was academic because of curriculum overload. Pre-clinical medical students were more stressful, because they were required to follow the fixed schedule. Pre-clinical medical students needed to adhere to stuff, like going to class early every day. Their life style was considered stressful and boring as well as they were just confined to lectures, laboratory and self-study18. Academic overload exposes students to stressful situations that was reflected on the level of student performance, lifestyle and health20. All mentioned studies indicated an elevated levels of stress which is considered as a chronic stress among medical students in Malaysian universities, especially in the pre-clinical stage. So, this issue required solutions that can help to reduce stress levels in students and improve quality of medical student’s life in Malaysian universities.
| Table 1: | List of stress studies that conducted in Malaysian medical schools |
HOW THE BODY RESPONDS TO STRESS?
Stress may affect human health through a myriad of behavioral and biochemical pathways due to some key hormonal and metabolic pathways21. In this way, chronic stress may influence a variety of physiological disorders through a biochemical cascade22,23. Stress starts in the brain and affects the brain as well as the rest of the body. Stress responses support adaptation and survival via responses of neural, cardiovascular, autonomic, immune and metabolic systems24. Stress is known leading to stimulate the sympathetic nervous system and hypothalamic pituitary adrenal (HPA) axis, resulting in the release of catecholamines and glucocorticoids25,26. Chronic stress may lead to overeating, co-elevation of cortisol and insulin and repression of certain anabolic hormones. This state of metabolic stress leads to increase abdominal fat27. The direct stress response and the accumulation of visceral fat both can elevate oxidative stress. This biochemical status conducive to several cell aging mechanisms, mainly inhibiting telomerase and leading to telomere length shortening and cells senescence28,29. Oxidative stress is defined as a defect in the balance between output of free radicals and reactive metabolites (antioxidants)30. This imbalance can conduct to harm important cells and biomolecules, with possible impact on the whole body31. Free radicals are unsettled molecules with electrons that could impair the cell membrane fatty acids and proteins, functioning by reacting with them32. Free radicals could be a predisposing factor for a lot of health problems because of their effects on mutation and DNA damage33. Free radicals are generated endogenously in human body or exogenously as well, when exposed to different physiochemical conditions or pathological states. Even though a low or moderate reactive oxygen species (ROS) have a good physiochemical effect including the killing of invading pathogens, wound healing and tissue renovation processes34. The disproportionate generation of ROS will badly affect homeostasis and causes oxidative tissue damage which is a big serious problem. The reverse impact of ROS can be limited by natural antioxidant pathways but also can be stimulated by many oxidative stressors contributing to tissue damage35. ROS are produced in response to exogenous and endogenous agents including stress response. Disorder of normal cellular homeostasis by redox signaling gives a shone in an actual disease for every organ36. So, free radicals and antioxidants have become commonly used terms in modern discussions of disease mechanisms37. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, NADPH oxidase isoforms (NOX), peroxidases, lipoxygenases (LOXs), xanthine oxidase (XO), glucose oxidase, nitric oxide synthase, myeloperoxidase (MPO) and cyclooxygenase (COX) are all enzymes that catalyze ROS-generating chemical reactions38,39. Intracellular compartments including mitochondria, the endoplasmic reticulum, nuclei, peroxisomes, the cytosol, plasma membranes and even extracellular spaces are capable of ROS generation40,41. The mitochondrial electron transport chain is the major site of ROS production in most mammalian cells42. All the previous studies reported increased oxidative stress and ROS in chronic stress cases43,44. Therefore, oxidative stress is a result to several disorders including chronic stress status that can be caused by academic reasons among medical students and this is not surprising. As previously presented, increased oxidative stress in the body causes a harmful increase in ROS, leading to countless physiological disorders.
OXIDATIVE STRESS AND WHITE BLOOD CELLS (WBC)
In chronic stress cases, the elevated levels of oxidative stress are linked to increased levels of ROS in tissues and in blood45. ROS are derived from endogenous sources and their production is not neutralized by antioxidant defense mechanisms. Increased levels of ROS production lead to positive-feedback with inflammation related mechanism through pro-inflammatory cytokines trigger ROS production and by ROS induced expression of proinflammatory cytokines41. Furthermore, ROS-induced apoptosis of skeletal muscle fibers is an important contributor to skeletal muscle fatigue and low exercise tolerance46. High levels of ROS have been demonstrated in the venous blood of chronic stress cases and are accompanied by high neutrophil superoxide anion generation47. Furthermore, the presence of ROS in circulating WBC in chronic stress cases leads to mitochondrial depolarization, which in turn leads to apoptosis of WBC48. Elevated WBC count has been shown to have a significant relationship with unfavorable lifestyles such as smoking, obesity, poor sleep and unhealthy diet, which is known to contribute to increase level of stress49. A previous study in Japanese male workers marked that poor sleep can be an independent risk factor for an increase in WBC count50. The WBC count has also been shown to have an inverse relationship with hour of work, which may have reflected poor sleep49. Polymorphonuclear leukocytes (PMNL) are one of the major kinds of inflammatory cells51. When the PMNL activated, it release reactive oxygen species, including hydrogen peroxide, contributing to endothelial damage diseases52,53. Stress response variables can lead to general fatigue that may be a key determinant of low-grade inflammation as represented by increase neutrophil counts48. The chronic secretion of stress hormone corticosterone and stimulation of the adrenal cortical cells with adrenocorticotropic hormone may result in endothelial dysfunction and initiate an acute phase inflammatory response involving the release of cytokines, acute phase proteins and increase neutrophils, decrease monocytes lymphocytes and increases neutrophil-lymphocyte ratio (NLR)54. So, chronic stress can lead to elevated total WBCs count due to increased oxidative stress that leads to high levels of harmful ROS.
OXIDATIVE STRESS AND RED BLOOD CELLS (RBC)
The RBCs are constantly risk to meet with both exogenous and endogenous sources of ROS that can harm the RBC and mess up its function55. To reduce the impact of the ROS in the oxidative stress status, RBCs have an antioxidant system constituting of both of, non-enzymatic low molecular weight antioxidants like glutathione and ascorbic acid and enzymatic antioxidants including superoxide dismutase, catalase, glutathione peroxidase and peroxiredoxin-2 (PRDX-2)56-58. ROS are very interactive and many of the ROS released from macrophages, neutrophils and endothelial cells into the plasma before they can be taken up by RBCs, especially in the microcirculation, because the RBCs more closeness to the blood vessels59,60. When the ROS entry into RBC cytoplasm, they are for the most part neutralized by the cytosolic antioxidant system. Hydrogen peroxide attached to RBCs rapidly reacts with catalase being converted to oxygen without any oxidation of haemoglobin (Hb)55. Slow autoxidation of Hb generates endogenous ROS with methaemoglobin production which has not the ability to carry oxygen and superoxide production that rapidly dismutases to form hydrogen peroxide61,62. The RBC cytosolic antioxidants neutralize the RBC bulk but the antioxidant system to neutralize the endogenous ROS is limited as the blood stream through the microcirculation when Hb becomes partially oxygenated63. Partial oxygenation results in an Hb conformational change with certain unique properties. Thus, there is a high increase in the rate of Hb autoxidation for partially oxygenated Hb62,64. The excess in the affinity of partially oxygenated Hb for the RBC membrane, limits the efficiency of the antioxidant system from neutralizing the ROS formed at the membrane65. This collection of un-neutralized ROS in the RBC leads to damage the RBC membrane impairing the flow of RBCs into the microcirculation and the transfer of oxygen to relevant tissues66,67. In addition, recent studies indicated that the RBCs also contain nicotinamide adenine dinucleotide hydrogen (NADH) oxidases, which can generate endogenous ROS68. The RBC membrane band 3 is the control of integral trans-membrane protein. It has several crucial functions including: The maintenance of anion homeostasis, thus, providing a link between the membrane and the cytoskeleton accountable for maintaining the cell shape and providing for the reactions of cytosolic proteins with the membrane through the amino terminal region that emerges into the cytosol. This region of band 3 binds competitively to both, Hb and a quantity of glycolytic enzymes69. The variations in Hb binding to band 3 as a function of the Hb oxygenation. Thus, couple Hb oxygenation, Hb autoxidation, glycolysis and ATP generation70. Oxidative damage to band 3 has been associated with RBC aging including the exposure of senescent specific neo-antigens that connect autologous IgG triggering RBC removal71. IgG binding has also been reported to be associated with band 3 clusters, which is triggered by the binding of denatured oxidized Hb (haemichromes) to band 372-74. Caspase-3 activation, which involves oxidative stress, further cleaves the cytoplasmic end of band 3 affecting the communications of band 3 with cytosolic proteins as well as the linkage to ankyrin and the cytoskeleton, which also motivates PS exposure75,76. The accelerates of older cells formation is known as membrane micro-vesiculation77. These changes affect the highly deformable biconcave shape maintenance which is necessary to pass through narrow pores, thus contributing to their removal from blood circulation, while cell shrinkage and vesiculation can be induced by different factors, some of which may not involve oxidative stress, the shrinkage related with potassium leakage via the Gardos channel is triggered by oxidative stress78. The damage of Ca-ATPase, which maintains a low intracellular concentration of free calcium ions79. Damage to Ca-ATPase is accountable for the age induced increase in intracellular calcium and is generated by oxidative harm to the ATPase80,81. The increase in the intracellular calcium activates the Gardos channel which leads to potassium leakage from the cell resulting in cell shrinkage and damage82,83. This increased also activates calpain, transglutaminase-2 and some caspases that can degrade/crosslink cytoskeleton proteins84. It also prevents phosphotyrosine phosphatase rising band 3 phosphorylation85. The RBC lipid bilayer contains an asymmetric distribution of phospholipids with PS being maintained on the inner cover of the membrane by the rivalry between scramblase, which randomizes the allocation and flippase, which internalizes the PS. In addition to the increase in sphingomyelinase which increases ceramide, intracellular calcium increase has been linked to the exposure of PS and to the decrease of Flippase activity86, which triggers the interaction of RBCs with macrophages and eryptosis87-89. Despite the important role of macrophages in RBCs removal, it is still not clear whether the RBCs macrophages interaction is the responsible cause of aging RBCs removal from circulation or not90,91.
OXIDATIVE STRESS AND THE GASTROINTESTINAL (GI) TRACT
The ROS aggressive effect has a tendency to the GI tract, they are also bared to outside environment with immune cells presence and intestinal flora dietary factors, all prospect sources of ROS92. Two main enzymatic reactions produce ROS in the GI tract, the hypoxanthine (HX)/XO system and the NADPH oxidase system93. The GI tract has the largest concentration of XO in the body, which along with various phagocytic cells and a great number of catalase-negative bacteria in the colon, join to generate large amounts of oxygen (O2‾)94. ROS have been linked with various GI tract disorders includes malabsorption90. The excessive levels of ROS can lead to damage cellular proteins including cytoskeletal proteins and ultimately disrupt GI tract barrier to increase gut permeability which contributes to inflammation in a variety of GI tract diseases95-97. Therefore, stress can be the cause of block the breakdown and assimilation of food for energy and nutriment. This malabsorption can then lead to a reciprocal negative effect to the stress and can be another cause of many health problems.
OXIDATIVE STRESS AND ANAEMIA
The WHO defines anaemia in adults as haemoglobin less than 130 g L–1 in males and less than 120 g L–1 in females. Anaemia is one of the most widespread disorders in the world, anaemia affects one-quarter of the world’s population and making it a global public health problem, with 1. 62 billion people affected between 1993-2005, approximately 48. 8% of the global population98. The cause of anaemia varies with age and sex. Dietary deficiency or malabsorption of haematinic factors like iron or vitamins like folic acid and vitamin B12 are the most important causes of anaemia99. Iron deficiency is the most common cause of anaemia by a defect in haemoglobin synthesis. Iron deficiency anaemia affecting about 500 million people worldwide. Moreover, the body has limited ability to absorb iron, Iron is present in food as ferric hydroxides, ferric-protein and heme-protein complexes100. Folate and vitamin B12 both are involved in the synthesis of tetrahydrofolate, an integral component of deoxyribonucleic acid synthesis and nuclear maturation. Shortage of vitamin B12 or folate can cause megaloblastic anaemia due to defect accounting for the asynchronous maturation of the nucleus is a defective DNA synthesis that leads to a characteristic abnormality in erythroblasts in the bone marrow (Fig. 1). Vitamin B12 is found in foods of animal origin, such as liver, meat, fish and dairy produce. Vitamin B12 is synthesized in nature by microorganisms by internal production from intestinal bacteria (not in humans) or by eating bacterially contaminated foods. Folate derived from folic acid (vitamin B9) compounds, it’s found most especially in foods of animal liver, greens and yeast100.
Based on the above, oxidative stress resulting in stressful people can lead to GI disorders including malabsorption, which leads to lack of important nutrients to the body including haematinic factors. Also, oxidative stress resulting in stressed individuals plays a role in damaging the RBC membrane and impairing it, or accelerating the aging and death of the RBC. Therefore, stress can be another cause of current health problems including anaemia (Fig. 2) but few studies have been shown the relationship and discussed it (Table 2). In study focusing the of impact psychological stress on serum iron and erythropoiesis in rats by using a communication box system, foot-shock stress and psychological stress were administered to the rats. In the 7th and 14th days after administration, 10 rats were executed, respectively and the femoral bone marrow and blood were collected for analysis of serum iron (SI), serum transferrin receptor (sTfR), serum ferritin (SF), Hb, RBC, red cell distribution width (RDW), mean corpuscular volume (MCV), serum erythropoietin (EPO) and bone marrow iron.
| Fig. 1: | Role of vitamin B12 and folate in megaloblastic anaemia101 |
| Fig. 2: | Mechanism of anaemia caused by academic stress |
For rats, analyzed on the 7th and 14th day in psychological stress group, femoral bone marrow iron was significantly reduced, serum iron was reduced, Hb was reduced, RBC count was reduced, MCV was reduced, RDW was increased, serum ferritin, transferrin receptor and EPO showed no significant changes in comparison with controls after 7th day of administration but serum ferritin and EPO were reduced while transferrin receptor increased after 14th day administration. Finally, after comparing the results with a control group after 7th day and 14th day of psychological stress administration concluded, serum iron and bone marrow iron showing significant reducing compared with controls, erythropoiesis was significantly inhibited, all of this leaded to anaemia103, Another study conducted in Al-Haweeja, Iraq, 200 females aged 20-40 years old (50 women/blood group) to study the prevalence of anemia and relation to psychological stress.
| Table 2: | List of most important research that linked stress to anaemia |
| Table 3: | List of anaemia studies that conducted in medical colleges |
The study was concluded to complete drop in both Hb and PCV indication a mild symptomatic anaemia, they are suffering mainly due to the deterioration in the quality of life in Al-Haweeja, due to degradation in their general circumstances e.g., economical, financial, political, civil war, recurrent pregnancy and malnutrition that altogether may have caused an inevitable psychological stress leading to anaemia102.
PREVALENCE OF THE ANAEMIA AMONG MEDICAL STUDENTS
Based on the above-mentioned factors, medical students distinguish them from other groups of society because of additional increased stress levels. So, medical students have a greater chance to be effected by disorders related to stress, including anaemia. There are some studies conducted worldwide to record the prevalence of anaemia among medical students but these findings almost are non-existent in Malaysian medical colleges (Table 3) as per available published data and records.
FUTURE RESEARCH
In last year’s there has been a growing appreciation of the issues of quality of life and stress in medical students as this might be affecting their learning and academic performance. Despite the widespread public belief that stress is factor leading to diseases, the biomedical community remains skeptical for this conclusion and need to be further investigated. However, these studies are lacking in medical schools. Authors are looking forward to conduct more studies about this critical issue in Malaysia to assess the prevalence of stress and their relation to increasing exposure to abnormal haematological indices in medical students including anaemia as one of the most prevalent health problems globally. Level of increasing knowledge and confirmation from previous studies, proved and evidenced, how stress can lead to abnormal haematological indices, which requires to be further investigated in the mechanism occurrence of it at molecular and cellular level as per reported and suggested opinions and recommendations. Increase awareness in the community about this problem via health education, preventive intervention with all medical students in Malaysia to reduce stress towards distress, can improve their lifestyle and nutritional status, because it is the significant factor in achieving an improved level of health and academic performance. Further attention must be afforded for this particular issue.
CONCLUSION
Looking at the cited literature, it is hypothesized in the conclusion that there is a correlation between stress in medical students and its effect on the haematological indices include elevated WBCs count, especially neutrophils as well as an increase chance of anaemia that leads to abnormal blood indicators different according to the type of RBCs deficits which led to anaemia. There are several reasons of stress among medical students that needs to more study and there is a need to more investigation in the relationship between oxidative stress and megaloblastic anaemia in medical students in Malaysia.