Further study needed on seafood-derived omega-3's healthy ageing potential: Cohort study
The study, published in BMJ, defined 'healthy ageing' as "survival without chronic diseases (i.e., cardiovascular disease, cancer, lung disease, and severe chronic kidney disease), cognitive and physical dysfunction, or death from other causes not part of the healthy ageing outcome after age 65".
The researchers sought to investigate the longitudinal association between serial biomarker measures of circulating omega-3 PUFAs and healthy ageing, and recruited participants from four communities in the US between 1992 and 2015.
Fatty acid follow-up
The final cohort had 2,622 adults with a mean age of 74 years and who were in generally good health at baseline, and the researchers followed up on them for the 22 years.
Their plasma phospholipid omega-3 PUFA levels were measured at baseline, six and 13 years to provide an objective assessment of four individual PUFAs: two mainly derived from seafood (EPA and DHA), one predominantly endogenous (DPA), and one derived mainly from plants (α-linolenic acid, or ALA).
The researchers also reviewed the participants' medical records and diagnostic tests, and subsequently reported that 89% of the participants experienced unhealthy ageing during the follow-up period, while the remaining 11% remained relatively healthy.
They also found, after multivariable adjustments, that higher levels of long-chain omega-3 PUFAs were linked to an 18% lower risk of unhealthy ageing.
In addition, the group with the highest cumulative mean concentrations of EPA from seafood had a 24% lower risk of unhealthy ageing than the group with the lowest concentrations.
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Individually, higher EPA and DPA — but not DHA — levels were associated with a respective 15% and 16% lower risk of unhealthy ageing.
When it came to the predominantly endogenously metabolised DPA, the three groups with the highest level of the fatty acid had an 18% to 21% reduction in risk when compared to the group with the lowest level.
DHA from seafood and ALA from plants, however, were not found to be linked to healthy ageing.
In terms of cardiovascular disease risk, the study's results were supported by previously published literature, but the effects of omega-3 PUFAs on the other components of unhealthy ageing as defined by the current study had been mixed or inconclusive in earlier research.
The researchers hypothesised that self-reported dietary data might have been partially responsible for this, as such data may be subject to measurement errors and recall bias.
To ensure clearer, more accurate results, the current study combined reported dietary data with repeated biomarker measurements to account for trends over time in individual omega-3 PUFAs.
Considerations before interpretation
The researchers also stated that there were a few points worth considering when interpreting the study's results.
Firstly, biomarker concentrations are a function of both dietary intake and metabolism, influenced by genetic and exogenous factors that are difficult to separate.
Despite the lack of a significant association between healthy ageing and DHA from seafood, they had observed that after adjusting for the consumption of fish, the link between became noticeable.
This implies that metabolically determined levels of DHA play a larger role in healthy ageing than DHA levels determined by diet.
The researchers added that primarily endogenously derived DPA acted as a metabolic intermediary between EPA and DHA, and that further investigation into the independent and combined impact of DPA with other omega-3 PUFAs in controlled feeding conditions were needed for their specific roles in healthy ageing to be better understood.
The second consideration was that the link between EPA and healthy ageing, and between combined EPA, DPA and DHA and healthy ageing, were significant only in the group with the highest levels of these omega-3 PUFAs.
As the study cohort was born in the 1910s and 1920s, they tended to enjoy long-term improvements in population-level socioeconomic resources, which could have influenced their longevity and health across their lifespan.
Since education attainment was one of the strongest covariates in the study, the researchers said there was a possibility of differential exposures to unmeasured socioeconomic resource-related chronic and acute stressors that could have affected the results.
Lastly, the median circulating concentrations of ALA across the cohort made up a mere 0.09% to 0.21% of total fatty acids, far lower than the concentrations of the other PUFAs, a factor that could have contributed to the lack of a significant association between plant-derived ALA and healthy ageing.
The researchers concluded: "In older adults, a higher cumulative level of serially measured circulating omega-3 PUFAs from seafood (EPA and DPA), but not DHA from seafood or ALA from plants, was associated with a higher likelihood of healthy ageing.
"These findings support guidelines for increased dietary consumption of omega-3 PUFAs in older adults.
"(However) epidemiological associations cannot infer causality, so we caution against using these findings to inform public health policy or nutritional guidelines.
"Following the WHO’s policy framework for healthy ageing, any evidence-based clues to improve health in later life are welcome, but additional efforts to accelerate this area of research are essential."
"Serial circulating omega 3 polyunsaturated fatty acids and healthy ageing among older adults in the Cardiovascular Health Study: prospective cohort study"
Authors: Heidi TM Lai, et al.