Starting in 1997, the study monitored elderly people living in Chicago and the surrounding areas. The researchers recorded participants’ eating habits and other lifestyle factors. Upon death, the brains of 286 elderly were examined for dementia and Alzheimer’s disease.
Ondine van de Rest explains, ‘This is the first study in which it was possible to conduct research on the presence of markers of dementia and Alzheimer’s disease in the actual brains of test subjects. As such, it enabled us to objectively view the association with fish consumption.’
The researchers found fewer markers of dementia and Alzheimer’s disease amongst elderly people who consumed fish at least once a week than amongst those who consumed fish less than once a week. Strikingly, this association was only present amongst carriers of APOE ε4, the gene that increases the risk of developing Alzheimer’s disease and dementia. However, given that this association was not consistently demonstrated in other studies, it is still too early to confirm that eating fish on a weekly basis has a positive role on people who are genetically prone to developing dementia.
We know that eating more fish entails consuming higher concentrations of heavy metals such as mercury, with long-term overconsumption of heavy metals potentially causing damage to the kidneys, liver, brain and nervous system. This was also true in this study – it demonstrated that the higher the intake of fish, the higher the concentrations of mercury. However, as these higher concentrations did not correlate with a greater number of markers of dementia, it was not the case that an increased intake of mercury had a negative impact on the brain. In general, the health benefits of consuming fish outweigh possible negative effects.
Fish as brain food
The Dutch Health Council’s Guidelines for a healthy diet (‘Richtlijnen Goede Voeding’), revised in 2015, reads: ‘Consume one portion of fish a week, preferably oily fish.’ The basis of this guideline is more on the beneficial effect eating fish has on cardiovascular diseases, however, this could also be good advice for maintaining a healthy brain. However, it is recommended to vary the type of fish consumed. Tuna, mackerel and eel can contain high concentrations of heavy metals. The same applies to crustaceans and shellfish, such as lobster, Chinese mitten crab, mussels, squid and octopus.
Previous epidemiological studies have already indicated that eating fish is associated with decreased cognitive decline and a reduced risk of dementia. Studies have also been conducted on the effect of fish oil supplements; however, the effect of fish oil on better maintenance of cognitive functioning has not yet been convincingly demonstrated.