Only five previous studies were known to investigate this association, although findings were inconsistent, with three of the studies reported benefits that were not statistically significant.
Based on the knowledge that Japanese people consume the highest per capita of seafood in the world, researchers sought to study the association between fish consumption and onset of dementia.
They published the study in the British Journal of Medicine.
Study design
Participants for this study were recruited from the Ohsaki Cohort 2006 Study, residing in Ohsaki city, Japan.
A total of 13,000 individuals aged 65 years and above without disability were analysed and followed for 5.7 years
Food frequency questionnaires were used to collect data on consumption of fish and other foods at baseline.
In this study, fish referred to raw/broiled/grilled fish as well as boiled fish paste.
Daily fish consumption was categorised into four quartiles: Q1 (lowest), Q2, Q3, and Q4 (highest).
Respondents in Q1 were the reference category.
The primary outcome of this study was the onset of dementia, defined as disabling dementia or incident functional disability according to the criteria of the LTCI system used in Japan.
The dementia scale is classified into six ranks (0, I–IV, and M) with rank M representing severe dementia-related behavioral disturbance that require medical intervention.
A rank exceeding I is typically used as an outcome measure of incident dementia because individuals who have mild or moderate dementia are classified as rank II.
Fish findings
This study reported that compared to Q1 (lowest fish intake), the hazard ratio for incident dementia was 0.77 for Q2, 0.74 for Q3 and 0.70 for Q4 (p<0.01).
The researchers said: “An inverse association between fish consumption and the onset of dementia was observed, suggesting the potential benefits of fish intake for dementia prevention.”
Japan is estimated to have 1.1 million elderly (33%) suffering from dementia by 2060, and researchers said this result may hint in preventing dementia, “bring(ing) huge benefit on our society in terms of quality of life, caregiver burden, costs for medical and long-term care.”
The Japanese diet include oily fish such as salmon, tuna, amberjack, and pacific saury.
The researchers explained fish contain n-3 fatty acids, such as eicosapentaenoic acid and docosahexaenoic acid, which are suggested to have preventive effects against cognitive decline.
Other nutrients in fish, such as vitamin A/carotenoids, vitamin B12, vitamin D, vitamin E, and selenium, are also known to have neuroprotective effects.
Limitations
However, there were some limitations acknowledged in this study.
One of which was the collection of fish consumption data only at baseline. Some of the study participants may have changed their fish intake during follow-up.
The researchers also thought their 5.7 years of follow-up was relatively short and may have compromised the results.
They suggested conducting future cohort studies with a longer follow-up period.
Source: British Journal of Medicine
https://doi.org/10.1017/S0007114519002265
“Fish consumption and risk of incident dementia in elderly Japanese: The Ohsaki Cohort 2006 Study”
Authors: Nozomu Tsurumaki, et al.
