A healthy plant-based diet reduces risk of dementia and depression

Aim

Dementia affects 55 million people globally, with depression affecting 5–10% of the European population (10% in the UK).

Depression in early life is linked to an increased risk of dementia, and depression in later life has been shown to be a prodromal sign of dementia. In the early and intermediate phases of most dementia types, there is a significant prevalence of anxiety and depression.

Although the relationship between dementia and depression is complex, they do share some of the same, largely modifiable risk and protective factors, including diet.

This study examined the association of plant-based diet indices (PDIs) with dementia and depression using data from the UK Biobank. 

Method

UK Biobank is a prospective population-based cohort study that includes data from half a million men and women (ages 39 to 72) recruited from the general population between 2006 and 2010.

The data includes detailed information on demographics, social, lifestyle, physical activity (PA), medical history, hospital records and mortality.

To determine the number of dementia and depression cases among participants, hospital inpatient records with information on admissions and diagnoses obtained from the Hospital Episode Statistics was used.

Inclusion criteria required that participants completed at least one Oxford WebQ online self-administered 24-hour diet assessment questionnaire.

Foods reported on the Oxford WebQ were sorted into 17 food groups (whole grains, fruits, vegetables, nuts, legumes and vegetarian protein alternatives, tea and coffee, fruit juices, refined grains, potatoes, sugar-sweetened beverages, sweets and desserts, animal fat, dairy, egg, fish or seafood, meat and miscellaneous animal-based foods) based on nutrients and culinary similarities.

These groups were then classified into three classes: healthy plant foods, less healthy plant foods and animal foods.

To calculate the PDI, foods in both plant food groups were assigned positive scores and foods in the animal food group were given reverse scores. To calculate healthy PDI (hPDI), foods in the healthy plant food group were given positive scores while the less healthy plant and animal food groups received reverse scores. For unhealthy PDI (uPDI), less healthy plant food group were given positive scores, and foods in the healthy plant and animal food groups received reverse scores. 

Key findings

180,532 participants were included in the analysis.

Within this population, there were 6,781 incident cases of depression and 1,248 incident cases of dementia.

Participants with the highest quintile of hPDI were older; had lower BMI, and higher PA; were less likely to smoke; consumed less total energy, and alcohol. Participants with the highest quintile of uPDI were older; had higher BMI, and lower PA; were more likely to smoke; consumed less total energy and alcohol.

For the incident dementia, hPDI appeared to be protective, with an HR of 0.82 when comparing extreme hPDI scores quintiles (95% CI: 0.68, 0.98; p for trend <0.01). Participants with the highest hPDI were also associated with a reduced risk of depression (HR: 0.92; 95% CI: 0.95, 0.99; p for trend = 0.01).

Higher uPDI was associated with a higher risk of depression. For 10-point increases in uPDI, depression risk was higher by 7% (95% CI: 3%, 11%; p < 0.001). 

The authors found no associations between animal food intake and dementia or depression risk. 

Mechanisms whereby the intake of a healthful plant-based diet may be associated with dementia and depression include increased intake of fibre, adding to the diversity and composition of the gut flora, high content of unsaturated fatty acids and the antioxidant components, such as vitamins and flavonoids, which have been proven to have anti-inflammatory effects.  

Conclusion

The authors of this study concluded that an unhealthy plant-based diet was linked to an increased risk of dementia or depression, whereas a healthful plant-based diet was linked to a decreased risk of these conditions.

Following hPDI (i.e., whole grains, fruits, vegetables, nuts, legumes and vegetarian protein alternatives, tea and coffee, fruit juices) was associated with a lower incidence of dementia or depression, whereas a higher intake of uPDI (i.e., refined grains, potatoes, sugar-sweetened beverages, sweets and desserts, animal fat, dairy, egg, fish or seafood, meat and miscellaneous animal-based foods) was positively associated with a higher risk of dementia or depression.

The authors call for these findings to be considered as a potential target for the prevention of dementia or depression in the general adult population and future policies should recommend a higher intake of high-quality plant foods.

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