In addition, it has shown to reduce depression and anxiety.
Findings of the study were published in International Journal of Geriatric Psychiatry. The RCT was conducted by researchers from Massey University.
Seventy-two adults between 60 and 90 took part in this trial.
One of the criteria they must meet is having a subjective memory complaint which was confirmed by a friend or family member.
They were then randomised into two groups, where the intervention group was given three capsules of fish oil per day – equivalent to a daily dosage of 1,491mg of DHA and 351mg of EPA.
The placebo group, on the other hand, was given three capsules containing a total of 1,857mg of linoleic acid per day.
The primary outcomes of cognition and wellbeing were measured using tests such as the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the National Adult Reading Test (NART).
The participants’ blood samples were also taken to analyse their red blood cell fatty acid profile and apolipoprotein E (APOE) ɛ4 allele.
APOE ɛ4 allele was analysed as carriers of this allele have been shown to be at a higher risk of age-related cognitive decline and Alzheimer’s disease (AD).
Sixty participants completed the trial in the end.
Finding 1: Cognitive health
There was no significant difference between the fish oil and placebo group for any of the cognitive measures.
This was despite a significant increase in red blood cell fatty acid concentrations of EPA, DHA, and omega-3 in the fish oil group as compared to the placebo group.
“The trial did not find a significant effect for DHA supplementation on cognition in older adults with MCI despite a significant increase in DHA and EPA concentrations,” the researchers said.
The findings were also different to previous studies by Sinn et al. and Lee et al.
In a trial by Sinn et al., older adults with mild cognitive impairment were divided into three groups, took either 1,670mg of EPA and 160mg of DHA, or 1.550mg of DHA and 400mg of EPA, and control for six months.
Findings showed that the fish oil group had significantly improved in initial letter fluency as compared to the control group.
In the trial by Lee et al., older adults were given a dose of 1,290mg of DHA and 450mg of EPA or placebo.
By the end of the 12-month trial, they showed significant improvement in short-term memory, working memory, and immediate verbal memory.
“Failure to replicate the results from Sinn et al. and Lee et al. may be due to differences in baseline concentrations of EPA and DHA, or due to the severity or type of cognitive impairment or a greater cognitive reserve,” the researchers said, explaining why the results of the current trial has differed from the previous ones.
Finding 2: Blood pressure
On the other hand, fish oil supplementation has shown a significant effect on systolic blood pressure, where systolic blood pressure increased more in the placebo group over the 12-month period than in the fish oil group.
For example, systolic blood pressure increased by 1.8mmHg from 145.9 to 147.7 in the fish oil group but went up by 10.7mmHg from 140.2 to 150.9 in the placebo group.
“Over half of participants were taking hypertension medication, and yet those who took the DHA supplement had a smaller increase in systolic blood pressure over the 12-month period, which suggests that fish oil may provide additional benefit alongside other treatments.
“The mechanisms by which n-3 PUFAs reduce blood pressure are via prostaglandins which cause vasodilation, anti-platelet aggregation, and control sodium and water retention.
“A meta-analysis of 31 fish oil RCTs found that reduction in blood pressure was dose-responsive and was strongest in those with hypertension,” the researchers said.
Finding 3: Depression, anxiety
Favourable results were also seen in depression and anxiety scores in the fish oil group.
Improvements were seen in the Geriatric Anxiety Inventory (GAI) and Geriatric Depression Scale (GDS).
In particular, GDS scores had significantly improved in APOE ɛ4 carriers in the fish oil group compared to ɛ4 carriers in the placebo group.
The GAI scores also significantly improved in ɛ4 carriers in the fish oil group as compared to ɛ4 carriers in the placebo group.
“The trial found that GDS and GAI scores improved in ɛ4 carriers in the DHA group, whereas GDS and GAI scores worsened in ɛ4 carriers in the placebo group. This result indicates that ɛ4 carriers may benefit from a DHA supplement with alleviating depression and anxiety symptoms.
“Despite no effect on cognition, the positive result in APOE ɛ4 carriers on depression and anxiety scores and on systolic blood pressure justifies further DHA trials,” the researchers said.
Source: International Journal of Geriatric Psychiatry
The effects of docosahexaenoic acid supplementation on cognition and well-being in mild cognitive impairment: A 12-month randomised controlled trial
Authors: Mengelberg et al.