Overweight or obesity could cause mental illnesses (like depression) or affect mental health by causing diseases like heart disease that lead to depression. It is possible that losing weight would improve mental health and trials of weight loss programmes do support this, but positive changes in mental health could occur because attending programmes creates a sense of affiliation and emotional support, rather than weight loss itself. Indeed, people who lose weight without programmes typically have worse mental health compared with people who stay the same weight, which may be because losing weight involves food deprivation and is followed by weight regain.
Here we propose using anonymised medical data to understand how excess weight links to developing mental illness and whether weight loss with intervention relates to mental illness risk. We will: (1) assess whether the risk of mental illness in people who are overweight relates only to people who develop weight related diseases, like type 2 diabetes and heart disease; (2) assess whether weight loss and weight fluctuation relate to the risk of developing mental illness; (3) assess whether referral to a weight management programme relates to development of mental illness.
This study will clarify whether and how being overweight relates to mental illness and whether weight loss with and without support relates to long-term risk of mental illness.
Overweight or obesity is associated with several mental illnesses. The immunometabolic impacts of excess weight on mental health have been shown in animal models and experimental studies, but whether cardiometabolic disorders and inflammation are the pathways linking obesity to mental illness development is uncertain. Such evidence can be provided by prospective research with long follow-up. Clinical trials show that receiving behavioural support for weight loss improves mental health in the short term, but population-based studies found contradictory evidence. However, it is unclear whether any effects would be large enough to cause mental illness. Moreover, the long-term changes in mental health after weight loss intervention is unknown because people usually regain weight, whereas trials have not followed participants for long enough.
We will establish a prospective cohort of adults registered with a GP practice 1 January 2000 till now and use multivariable Cox regression analyses to: 1) investigate the mediating role of cardiometabolic disorders and inflammation in the association between excess body weight and mental illness risk; 2) estimate the association between weight change (classified into weight loss, weight gain, weight maintenance, and weight fluctuation) and mental illness risk. We will establish a matched cohort of adults who are referred to a weight loss intervention and five matched controls and use multivariable Cox regression analyses to assess the association between referral to a weight loss intervention and incident mental illness.
This study will offer insights into the mechanisms linking obesity to mental illness development and such knowledge could be used to partly treat or ameliorate potential harms from intervening on weight. Moreover, it will advance our knowledge on whether weight change is associated with mental illness risk in a real-world setting and the possibility of using a weight loss intervention to prevent mental illness development.
Outcomes of interest comprise first-onset diagnoses of individual mental illness or first prescriptions for selected medications, or referrals to mental health services.
1) Diagnoses of specific mental illness (as below) during clinical consultation. The date of first occurrence of each mental illness [single episode] and diagnosis will be extracted.
• Depression
• Anxiety
• Eating disorders
• Serious mental illness
o Schizophrenia
o Bipolar disorder
o Other psychotic mood disorders
2) Prescriptions for psychotropic medications, including antidepressant (except amitriptyline), anxiolytic, antipsychotics, and mood stabilisers. The date of each prescription will be extracted.
3) Referrals to mental health services (such as clinical psychology, psychotherapy, and outpatient mental health services), or being admitted to psychiatric hospital. The date of being referred and the type of referrals will be extracted.
Min Gao - Chief Investigator - University of Oxford
Min Gao - Corresponding Applicant - University of Oxford
Aurora Perez-Cornago - Collaborator - University of Oxford
Cynthia Wright Drakesmith - Collaborator - University of Oxford
Joseph Firth - Collaborator - University of Manchester
Mika Kivimaki - Collaborator - University College London ( UCL )
Paul Aveyard - Collaborator - University of Oxford
Shanquan Chen - Collaborator - London School of Hygiene & Tropical Medicine ( LSHTM )
Stella Haffner - Collaborator - University of Oxford
Xue Dong - Collaborator - University of Oxford
Xue Dong - Collaborator - University of Oxford