This thesis presents the Nutrients for Mental Health, Anxiety and Depression (NoMAD) study, a randomised, double blind, placebo controlled trial exploring the effectiveness of using a broad spectrum micronutrient product compared to a matched placebo in improving symptoms of anxiety and/or depression. There is growing evidence that micronutrients can improve mental health symptoms, particularly for people with specific diagnoses of clinical conditions such as ADHD or in the aftermath of traumatic events to prevent the development of PTSD. Previous trials investigating micronutrients as a treatment for anxiety and/or depression have struggled with small sample sizes, heterogeneity of products and timeframes and have often recruited populations with limited symptoms of anxiety and depression. It was hypothesised that micronutrients would outperform a placebo in a population of individuals with impairing symptoms of anxiety and/or depression. One hundred and fifty participants describing functionally impairing symptoms of anxiety and/or depression were randomised to receive either a micronutrient formula or a matched placebo. Participants completed a two-week baseline phase before moving into a ten-week randomised controlled phase, whether they received either the micronutrient or the placebo product. Mood and anxiety were measured primarily using the Patient Health Questionnaire-9, the Generalised Anxiety Disorder Scale- 7 and the Clinical Global Impression-Improvement scale, alongside other disorder-specific secondary outcome measures. Linear mixed effects modelling indicated significant improvements in both groups, with the micronutrient group improving significantly more quickly on both measures of anxiety (t = -2.23, p = 0.03) and depression (t = -2.17, p = 0.03). Forty-four percent of the placebo group were deemed responders on the CGI-I, compared to 49% of the micronutrient group. Both the placebo and the micronutrient were found to be as effective as other evidence-based treatments. Further analysis demonstrated a reduced response to the placebo for specific subgroups; older participants, men, participants who had previously trialled psychiatric medication and participants from lower socioeconomic groups. There was a single between-group difference on treatment-emergent side effects; participants in the micronutrient group were significantly more likely to report increased bowel motions compared with the placebo group. There were no serious adverse events recorded during the trial and the blind was adequately maintained for both groups.

Both the placebo and micronutrient interventions generated significant improvements in symptoms of anxiety and depression across the course of the trial, although for participants in some subgroups, they demonstrated a poorer response to the placebo. Future research in this area should focus on effectiveness for specific disorders and the impact of micronutrients on resilience or general measures of functional improvement.