The association between fermented dairy food intake and incident depression and dementia in older Australians

Depression and dementia represent significant public health issues, affecting approximately 1 in 10 and 1 in 12 older Australians, respectively. While current pharmacological treatments are effective in relieving symptoms, they often entail undesirable adverse effects, including gastrointestinal issues and bradycardia (1,2) . This highlights the need for primary preventative measures, including food- and nutrition-based approaches. Chronic brain inflammation is believed to interfere with the gut–brain axis (3) . Consumption of fermented dairy products rich in beneficial gut microbes may attenuate this inflammation and offer protective health benefits. This study aimed to examine whether fermented dairy intake could mitigate the risk of incident depression and dementia. Utilising data from the Sydney Memory and Ageing Study I of 1037 participants 70–90 years, 816 participants (mean age: 76.7) were followed from 2005 until 2012 for incident depression, and 974 participants (mean age: 80.7) were followed up from 2005 until 2014 for incident dementia. Fermented dairy intake was assessed using the Dietary Questionnaire for Epidemiological Studies version 2 and categorised yoghurt and regular cheese into quartiles (Q) and low-fat cheese into consumers/non-consumers, with no consumption as the reference group. Depression diagnoses were assessed via self-reported physician-diagnosed history, medication use, service utilisation, and heavy alcohol use. Dementia diagnoses followed the criteria in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders. Cox proportional hazards models examined the associations between fermented dairy intake and the risk of incident depression/dementia. Additionally, linear regression models were applied to assess for depressive symptoms score (measured by the Geriatric Depression Scale-15) and psychological distress score (measured by the Kessler Psychological Distress Scale-10). All models were adjusted for sociodemographic, lifestyle factors, and medical histories. Over a median follow-up of 3.9 and 5.8 years, 120 incident depression and 100 incident dementia cases occurred, respectively. Those who consumed high yoghurt (Q4: 145.8–437.4 g/day) and low-fat cheese (consumers: 0.4–103.1g/day) intakes were associated with a lower risk of incident depression, both compared to non-consumers (yoghurt: adj.HR: 0.38, 95% CI: 0.19–0.77; low-fat cheese: adj.HR: 0.50; 95% CI: 0.29–0.86). They were also associated with lower depressive symptom scores (yoghurt: adj.β = −0.46; 95% CI: −0.84, −0.07; low-fat cheese: adj.β = −0.42; 95% CI: −0.73, −0.11). However, those who consumed a higher intake of regular cheese (Q4: 14.7–86.1 g/day) had an elevated risk of incident depression (adj.HR: 1.88; 95% CI: 1.02, 3.47), and those in Q2 (0.1–7.2 g/day) had significantly higher depressive symptom scores (adj.β = 0.42; 95% CI: 0.05, 0.78). No significant findings were found for psychological distress scores or incident dementia. Our findings of a cohort of older Australians suggest that higher yoghurt and low-fat cheese intakes may reduce incident depression and depressive symptoms, while a higher intake of regular cheese may increase these risks.