Mental illness affects 37% of the adult population over a typical year in the European Union , and about 50% of the population over the average lifetime in the USA , although figures are slightly lower in less industrialised nations. Recent, large, well-conducted studies suggest that Schizophrenia and Bipolar disorder affect 1% of the population between them, Depression about 5%, and Anxiety states at least as many again. Approximately 8% of the population are dependent upon or abuse alcohol or illicit drugs, and 5% or so of those over the age of 60 have Dementia. To these figures can be added the 1% of people with Autism, 1% with Attention Deficit Hyperactivity Disorder, the 2-3% or so with Eating Disorders and 3-4% with Learning Difficulties .
Some people may find these figures very high, maybe even difficult to believe. You might ask: “Where are all these people? I don’t know anyone who’s mentally ill.” But if you stop to think for a moment, most of us do know workmates, friends or family who are or have been affected – even if we and they may not want to think so. Add in the concentration of mental illness in certain other populations, like those on benefits and in prisoners, and the numbers above seem realistic.
It has to be said that these striking figures do include mild cases, which can be self-limiting. Even mild disorders however are by definition disabling, in that they restrict daily activities – and they also increase the risk of more severe problems with the passage of time.[3-5] Thus, the World Health Organisation (WHO) Global Burden of Disease Study  found that mental and behavioural disorders account for about 23% of all the Years Lived with Disability globally. This is higher than any other disease category. Depression, anxiety states, alcohol and drug-use disorders, schizophrenia and bipolar disorder all rank amongst to the top 20 most disabling conditions that affect mankind. Depression, for example, is on average more subjectively disabling than angina, asthma, arthritis or diabetes. Mental illness also increases mortality, and not just from suicide. The most common causes of death in the mentally ill are cardiovascular disease and cancer, as in the rest of the population. But these kill people with schizophrenia, bipolar disorder, depression, substance misuse, dementia and learning disabilities a decade or more earlier than in the general population.[8-10] (Incidentally, it is only because we have standardised diagnostic criteria for mental illness – see last weeks’ blog – that we can make any of these comparisons.)
This combination of prevalence and disability, often from a young age, makes mental illness very costly to society. As researchers from the London School of Economics have recently shown, “mental illness is now nearly a half of all ill health suffered by people under 65 and it is more disabling than most chronic physical disease”. Similarly, both the Cost of Disorders of the Brain in Europe Study Group  and the World Economic Forum  have calculated that the total costs of mental illness are much more than those associated with all the other major disease categories including diabetes, cancer and cardiovascular disease. Yet only a minority of people with mental illness receive adequate treatment.[11-13] The stigmatisation of mental illness contributes to this treatment gap, by putting people off seeking help, rendering doctors less likely to investigate or treat physical illness in the mentally ill, and through the relative under-funding of mental health services. Amazingly, even though UK health services only aim to spend 13% of their budgets on mental health, based on the WHO Disability Adjusted Life Years statistic (which gives a higher weighting to mortality), most of them don’t even manage that! 
 Wittchen, H.U. et al. Eur Neuropsychopharmacol 21, 655-79 (2011).
 Kessler, R.C. et al. Arch Gen Psychiatry 62, 617-27 (2005).
 Demyttenaere, K., et al . JAMA 291, 2581–2590 (2004).
 Eaton W.W., et al. Epidemiol Rev 30, 1-14 (2008).
 American Psychiatric Association. DSM-5.( 2013).
 Vos, T., et al. Lancet 380, 2163-2196 (2012).
 Moussavi, S., et al. Lancet 370, 851-8 (2007).
 The Schizophrenia Commission. The abandoned illness: a report from the Schizophrenia Commission (London, 2012).
 CIPOLD team. Confidential Inquiry into premature deaths of people with learning disabilities (Norah Fry Research Centre, University of Bristol, 2013).
 Chesney, E., et al. World Psychiatry 13, 153-60 (2014).
 The Centre for Economic Performance’s Mental Health Policy Group. How mental illness loses out in the NHS (London School of Economics and Political Science, 2012).
 Gustavsson, A., et al. Eur Neuropsychopharmacol 21, 718-79 (2011).
 Bloom, D.E., et al. The global economic burden of non-communicable diseases (World Economic Forum, 2011).
 Chief Medical Officer (CMO) annual report: public mental health. (DOH, London 2014).