Depression is one of the most prevalent mental health conditions and can affect people of all ages, but it is becoming more common among the older population with increasing life expectancy. Observational studies have found poor micronutrient status (particularly folate and vitamin B12) to be associated with an increased risk of depression in older people. Supplementation with folic acid has been shown to enhance anti-depressant drug treatment and there is preliminary evidence that supplementation with certain micronutrients may help improve depressive symptoms in older patients. There has also been a lot of interest in the role of long-chain omega-3 fatty acids in depression. However, the evidence from randomized controlled trials is limited and difficult to evaluate owing to considerable variability between studies. The research highlights the importance of a healthy diet and lifestyle to help maintain good mental health into old age and health professionals should try to support older people in trying to achieve this.