Malnutrition and nutrient deficiencies are more likely to be a consequence rather than a cause of mental illness in older people. Classical single deficiency states as cause of mental illness are rare in developed countries though there is a strong suspicion that suboptimal nutrition often contributes to ill health in old age. The immediate significance of single deficiency states is confined to a few specific circumstances, for example, thiamine deficiency and the Wernicke–Korsakoff syndrome; B12 and folate with cognitive impairment, dementia and depressive states¹⁹. In most instances, the import of nutritional status on mental function is less direct and more subtle.

Certainly, the consequences of malnutrition will complicate treatment of mental illness and impair prospects for recovery. In addition, effects on physical strength, organ function and the immune system increase the risk of falls, fractures, pressure sores, infection, hospital admission and mortality. These risks will need to be addressed in care plans and will substantially increase the hazards associated with prescribing psychotropic drugs to older people.

Under-nutrition may arise from quantitative and qualitative dietary inadequacy, and a number of problems facing older people and the mentally ill place them at particular risk. Social isolation, loneliness, poor socioeconomic position, physical and sensory disability and co-morbid long-term conditions are common accompaniments of mental health problems in later life. Depression and dementia, in particular, are associated with reduced appetite, weight loss and poor attention to diet resulting from apathy, loss of interest and cognitive difficulties. Furthermore, effects of nutrient deficiency, including apathy, depression and cognitive impairment, will compound an already difficult situation and may lead to a spiral of decline.

The overwhelming priority in the management of under-nutrition among elderly populations is prevention. A major impetus must ultimately come from changes in public policy that improve the older person’s social, material and financial position in society, address inequalities and ensure the efficient provision of services to those in need.

The market-led approach to nutrition that operates in many food-rich countries has been found to increase the disparity between the nutrition and health of the rich and poor²⁰. The provision of domiciliary care services is inequitably distributed, often inefficiently organized and frequently determined by demand rather than need²¹. In the UK a younger person with equivalent need to an older person has much greater access to social care and mental health services^22,23.

In the modern era food suppliers are often large impersonal stores sited some distance from communities, making shopping difficult for physically and mentally disabled people. Low income with disability not only restricts ability to afford a protective diet but also limits access to retailers where healthy food can be purchased more cheaply. Local shops in developed countries are less prevalent and can be significantly more expensive than distantly sited supermarkets²⁴.

Often the presentation and supervision of meals is poor. This is particularly evident in hospitals and care homes. A leading charity for older people in the UK²⁵ has drawn attention to the problem in hospitals and this report along with other national guidelines recommends a number of changes to practice that could address this need^13,26. The National Diet and Nutrition Survey in the UK found the food supply in care homes to be sufficient but biochemical measures revealed poor vitamin and mineral status³. While the explanation of this is not clear it may be the result of poor intake and absorption due to poor presentation and timing of food, need for more assistance with eating or changes in absorption and the general medical condition.

Simple measures like providing meals in a form that is appealing and easily edible, at a time when appetite is greatest or when people are most motivated, providing assistance and allowing enough time for meals to be eaten are often all that is required yet all too often not part of the regimes of hospitals or care homes. Some people, particularly people with dementia, will take food from family or friends and not care staff or from certain care staff, and these institutions need to provide greater flexibility of approach and ensure that areas catering for older people and people with dementia have sufficient number of staff. The ready availability of fresh produce, particularly fruit and vegetables, is lacking. Modern catering is not always sensitive to the needs and preferences of older people.

Diet is a poor source of vitamin D, which depends on exposure to ultraviolet light for its formation. More exposure to natural sunlight is the most important preventive measure but for those older people at risk of little exposure, calcium and vitamin D supplements are recommended²⁷.

Easy access to health and dental care is important. People with long-term conditions and poor dentition are at particular risk of dietary deficiency. Dental care is especially overlooked yet a study of hospitalized people aged 61–99 years found 60% to have disease of the oral soft tissue²⁸. For those living in the community, preventive dental and health care with early recognition and treatment of illness is needed.

The elderly population may benefit from greater education and advice about healthy and affordable eating, issues normally targeted at younger people. The judicious use of fruit juice, frozen foods and some convenience foods might ease the burden of food preparation in those at risk of neglecting their diet. Occupational therapy assessments can find practical solutions to problems arising from visual impairment, arthritic joints and disability or the need for someone to help with shopping and food preparation. The teaching of culinary skills may be particularly helpful to the older bereaved man who never cooked while his wife was alive.

Diet is connected with lifestyle and opportunity and so moderate alcohol consumption is associated with better health and less risk of developing depression but also with a more active and sociable lifestyle, better self-rated health status²⁹ and higher intake of various nutrients³⁰. Whether these variables are independent is not clear but the evidence would suggest that older people who can remain active, exercise and remain socially connected seem to take a better diet and protect themselves from some of the mental health problems occurring in later life.

In a prospective study of relatively healthy and active European men aged 70–89 years, low cholesterol but not dietary factors was associated with increased risk of developing depression³¹. The relationship of cholesterol levels to mental health in later life remains confusing as, while raised levels might suggest increased vascular risk, high levels may reduce risk of dementia, with declining levels reported before incident dementia³².

Recommendations for the treatment of malnutrition and the maintenance of optimal nutrition are available¹³