Mediterranean diet and depression: a population-based cohort study

Background Depression imposes immense public health burden, demonstrating an urgent need of the identification of modifiable risk factors. Only a few cohort studies have analyzed the association between Mediterranean dietary pattern (MDP) and depression but with mixed results. We examined the impact of MDP on clinically ascertained depression in a large population-based dataset. Methods In 1991/92, detailed information on diet, using a food frequency questionnaire, and potential confounding factors (body weight, height, educational attainment, smoking, previous diabetes and hypertension, and physical activity) was collected, in a random sample of 49,261 Swedish women aged 29-49. Adherence to MDP was calculated. Clinical depression was extracted from the National Patient Register. Study participants were followed up through 2012. Results During an average follow-up of 20.4 years, 1677 incident cases of depression were diagnosed. We observed a lower risk of depression for medium (score 4-5) and high (6-9) adherence to MDP, compared with low (0-3) adherence (Medium: hazard ratio (HR) = 0.90, 95% confidence interval (CI) = 0.81-1.00; High: HR = 0.82, 95%CI = 0.71-0.94). Per unit increase of adherence, the risk of depression was reduced by 5% (HR = 0.95, 95%CI = 0.92-0.98). The association became stronger when restricting to severe form of depression (HR = 0.51, 95%CI = 0.33-0.76). The HRs were higher from age 50 onward both over the first and the second 10-year follow-up period, compared with before age 50, indicating stronger association with increasing age. Results remained after extensive sensitivity analyses. Conclusion Higher adherence to a Mediterranean diet at middle age was associated with a lower risk of depression later in life among Swedish women.