Introduction
Schizophrenia is a debilitating condition that affects 1% of the population worldwide [1]. Symptoms of schizophrenia are delineated into positive and negative symptoms; the former include hallucinations, paranoia and delusions, and examples of the latter are reduced motivation, impoverished speech, blunted affect and social withdrawal; in addition this over-arching label can be further sub-grouped based on symptom profile [2]. These symptoms generally emerge in early adulthood and often persist in approximately three-quarters to two-thirds of individuals despite optimal treatment [3-5]. This enduring and/or fluctuating course of illness leads not only to personal distress and disability but also engenders a high societal burden with the estimated total financial cost of £11.8 billion per annum in England alone [6]. Furthermore schizophrenia patients often have comorbid addiction, anxiety and depressive disorders [7], asthma, chronic obstructive pulmonary disease, type-2 diabetes and numerous diabetic-related complications [8] and have increased premature mortality due to underdiagnosed ischemic heart disease and cancer [9,10]. Indeed, in comparison with the general population those with schizophrenia have a two- to three-fold higher mortality rate, which equates to a 10–25-year reduction in life span [11]. Therefore, there is a need to continually develop and evaluate novel treatments for this disorder, not only for the benefit of the patients but also for the wider society.
Currently, anti-psychotic medication (with or without psychotherapy) is the main treatment for individuals with schizophrenia, an intervention that led to the dopamine (DA) hypothesis. This enduring theory of schizophrenia has evolved over time and was first based upon clinical observations and subsequently empirical evidence from anti-psychotic treatment studies [12]. Briefly, in the 1970s the DA hypothesis initially pinpointed the role of excessive dopamine in schizophrenia [13], which was later refined to include region specificity in terms of prefrontal hypodopaminergia and a subcortical hyperdopaminergia [14]. However, neither of these conceptualisations accounted for the aetiology of dopaminergic abnormality and hence there was a further modification of the DA hypothesis as a ‘final common pathway’ in which numerous genetic and environmental factors can result in increased presynaptic striatal dopaminergic function [15].
Although anti-psychotic medication has persisted as the optimal treatment and is effective in managing the positive symptoms it is limited in terms of treating negative symptoms [16]. In addition to this drawback of drug treatment, this type of therapy is based solely on symptomatology and dosage is often determined by a process of trial and error [17]. In those who respond to anti-psychotic medication, side effects can be distressing and often intolerable; these include involuntary movements such as tremor and rigidity, drug induced Parkinson’s, Tardive dyskinesia, hyper-salivation, increased heart rate, metabolic syndrome and weight gain. Often the side effects themselves require further pharmacological treatment and/or result in treatment discontinuation, leading to subsequent relapse. Furthermore, approximately one-third of individuals with schizophrenia do not respond to anti-psychotic medication, either alone or in conjunction with psychodynamic counselling and other pharmacotherapy [18].
However, there is now increasing evidence that a number of physiological mechanisms such as oxidative stress, one carbon metabolism and atypical immune-mediated responses exist in individuals with schizophrenia, not solely dopaminergic pathophysiology as per the DA hypothesis. Furthermore, these differing pathophysiological manifestations may be ameliorated by nutritional treatment strategies. Therefore, this article aims to briefly outline the aforementioned probable underlying contributory mechanisms that have been observed in patients diagnosed with schizophreniaa and review the research and clinical evidence that has evaluated nutritional interventions in addition to anti-psychotic medication for schizophrenia.
Introduction
Schizophrenia is a debilitating condition that affects 1% of the population worldwide [1]. Symptoms of schizophrenia are delineated into positive and negative symptoms; the former include hallucinations, paranoia and delusions, and examples of the latter are reduced motivation, impoverished speech, blunted affect and social withdrawal; in addition this over-arching label can be further sub-grouped based on symptom profile [2]. These symptoms generally emerge in early adulthood and often persist in approximately three-quarters to two-thirds of individuals despite optimal treatment [3-5]. This enduring and/or fluctuating course of illness leads not only to personal distress and disability but also engenders a high societal burden with the estimated total financial cost of £11.8 billion per annum in England alone [6]. Furthermore schizophrenia patients often have comorbid addiction, anxiety and depressive disorders [7], asthma, chronic obstructive pulmonary disease, type-2 diabetes and numerous diabetic-related complications [8] and have increased premature mortality due to underdiagnosed ischemic heart disease and cancer [9,10]. Indeed, in comparison with the general population those with schizophrenia have a two- to three-fold higher mortality rate, which equates to a 10–25-year reduction in life span [11]. Therefore, there is a need to continually develop and evaluate novel treatments for this disorder, not only for the benefit of the patients but also for the wider society.
Currently, anti-psychotic medication (with or without psychotherapy) is the main treatment for individuals with schizophrenia, an intervention that led to the dopamine (DA) hypothesis. This enduring theory of schizophrenia has evolved over time and was first based upon clinical observations and subsequently empirical evidence from anti-psychotic treatment studies [12]. Briefly, in the 1970s the DA hypothesis initially pinpointed the role of excessive dopamine in schizophrenia [13], which was later refined to include region specificity in terms of prefrontal hypodopaminergia and a subcortical hyperdopaminergia [14]. However, neither of these conceptualisations accounted for the aetiology of dopaminergic abnormality and hence there was a further modification of the DA hypothesis as a ‘final common pathway’ in which numerous genetic and environmental factors can result in increased presynaptic striatal dopaminergic function [15].
Although anti-psychotic medication has persisted as the optimal treatment and is effective in managing the positive symptoms it is limited in terms of treating negative symptoms [16]. In addition to this drawback of drug treatment, this type of therapy is based solely on symptomatology and dosage is often determined by a process of trial and error [17]. In those who respond to anti-psychotic medication, side effects can be distressing and often intolerable; these include involuntary movements such as tremor and rigidity, drug induced Parkinson’s, Tardive dyskinesia, hyper-salivation, increased heart rate, metabolic syndrome and weight gain. Often the side effects themselves require further pharmacological treatment and/or result in treatment discontinuation, leading to subsequent relapse. Furthermore, approximately one-third of individuals with schizophrenia do not respond to anti-psychotic medication, either alone or in conjunction with psychodynamic counselling and other pharmacotherapy [18].
However, there is now increasing evidence that a number of physiological mechanisms such as oxidative stress, one carbon metabolism and atypical immune-mediated responses exist in individuals with schizophrenia, not solely dopaminergic pathophysiology as per the DA hypothesis. Furthermore, these differing pathophysiological manifestations may be ameliorated by nutritional treatment strategies. Therefore, this article aims to briefly outline the aforementioned probable underlying contributory mechanisms that have been observed in patients diagnosed with schizophreniaa and review the research and clinical evidence that has evaluated nutritional interventions in addition to anti-psychotic medication for schizophrenia.
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