Recent findings from the international journal of cancer shed light on the complex relationship between polyunsaturated fatty acids and cancer risk across multiple types.
Study: Associations of plasma omega-6 and omega-3 fatty acids with overall and 19 site-specific cancers: A population-based cohort study in UK Biobank. Image Credit: Antonina Vlasova/Shutterstock.com
Numerous studies have investigated the relationship between polyunsaturated fatty acid (PUFA) intake and cancer risk, but definitive evidence remains elusive.
In a recent study published in the International Journal of Cancer, researchers analyzed plasma concentrations of omega-3 and omega-6 PUFAs to identify potential associations with overall cancer incidence and the incidence of 19 specific types of cancer across various sites.
Why are PUFAs important?
A diet rich in polyunsaturated fatty acids (PUFAs) is thought to reduce cancer risk and improve survival rates in cancer patients. The potential protective mechanisms of PUFAs include their role as substrates in lipid pathways, which produce both pro- and anti-inflammatory mediators. Additionally, PUFAs may alter cell membrane composition, thereby influencing cell signaling pathways.
However, conclusive evidence for these effects is limited. This study used data from the UK Biobank, which provides extensive data on a cohort of over 500,000 individuals followed since 2006, to explore this hypothesis. A random subset of approximately 60% of the cohort recently underwent plasma metabolomic testing, which served as the basis for this study.
The authors had previously shown that plasma levels of omega-3 and omega-6 PUFAs were associated with a protective effect against cancer mortality.
Study participants
The researchers analyzed data from 29,838 UK Biobank participants with cancer, followed for an average of 12.9 years. The participants had a mean age of 56.4 years, and nearly 91% were White. Those with higher PUFA levels tended to be female, lighter in weight, more physically active, and less likely to smoke. Individuals with higher omega-3% levels were typically older than those with higher omega-6% levels.
The team compared blood levels of omega-3 and omega-6 PUFAs to cancer risk, expressed as a percentage of total fatty acids (omega-3% and omega-6%).
Associations between PUFA levels and cancer risk
Cancer incidence declined across increasing quintiles of both omega-3% and omega-6%. Specifically, for each standard deviation (SD) increase, cancer risk decreased by 2% for omega-3% and 1% for omega-6%. (One SD increase corresponded to 3.63 percentage points for omega-6 and 1.55 for omega-3.)
Among the 19 specific cancer types analyzed, omega-6% was inversely associated with 12 cancer types and omega-3% with five. Both PUFAs showed overlapping inverse associations for stomach, colon, hepatobiliary tract, and lung cancers.
However, four cancer types were not associated with either PUFA, while prostate cancer showed a 3% increased risk per SD increase in omega-3%, and blood cancers trended towards a positive association with omega-6%.
Omega-6/Omega-3 Ratio and Cancer Risk An increase in the omega-6/omega-3 ratio was associated with an elevated overall cancer risk, as well as an increased risk for three specific cancers. Notably, rectal cancer risk rose by 2% per SD increase in the omega-6/omega-3 ratio, even after adjusting for factors like BMI, smoking, alcohol intake, and physical activity.
Influence of other factors
Inverse associations between omega-6% and cancer risk were stronger in younger participants (under 65) and females. Conversely, the protective effect of omega-3% was stronger in older adults, males, and current smokers.
A non-linear association was noted for omega-3%, suggesting greater protection at lower concentrations, while omega-6% posed the highest risk at intermediate levels.
Significance of this study
Unlike previous studies that focused on dietary intake of PUFAs, this study examined plasma PUFA levels. Prior research has suggested that increased omega-3 intake is protective against cancer mortality, and omega-6% is protective against cancer incidence, findings consistent with this analysis.
Additionally, the authors previously found a positive association between a high omega-6/omega-3 ratio and increased mortality from cancer, cardiovascular disease, and other causes, suggesting a greater impact of omega-3 relative to omega-6.
This study demonstrates that blood biomarkers are likely superior to dietary intake assessment as they capture all intake sources, improve measurement accuracy, and enhance statistical power.
Future studies should explore the relationship between omega-3 PUFAs and prostate cancer, as some evidence suggests a possible increased risk with long-chain omega-3 PUFAs.
Conclusions
The findings indicate “small inverse associations of plasma omega-6 and omega-3 PUFAs with the incidence of overall and most site-specific cancers.” It also showed an increased risk of prostate cancer with omega-3 PUFAs, though this remains to be validated in other studies. If confirmed, these results could support dietary interventions to prevent cancer.
