Comments on “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”

I have read with great interest the article entitled "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" by Zhang et al.1 who conducted a prospective study to evaluate the effect of plasma levels of omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) on cancer risk. The adjusted hazard ratios (HRs) (95% confidence intervals [CIs]) of omega-6% and omega-3% for overall cancer incidence were 0.98 (0.96–0.99) and 0.99 (0.97–1.00), respectively. Among specific sites, risk reduction in cancers of the esophagus, colon, pancreas, and lung by higher plasma omega-6% and omega-3% PUFAs were observed. But a total amount of PUFAs and total fatty acids were not considered for the analysis, and plasma omega-6/omega-3 ratio was not significantly associated with overall and specific sites of cancers in supplemental data. The plasma levels of omega-3 and omega-6 PUFAs were expressed as percentages of total fatty acids (omega-6% and omega-3%), and I have queries about the risk assessment indicators. Wang et al.2 examined the association of omega-3 PUFA consumption and the incidence of digestive system cancers. The pooled relative risk (RR) (95% CI) of omega-3 PUFAs intake for digestive system cancers was 0.83 (0.76–0.91). They used the absolute amount of intake for a meta-analysis. Huybrechts et al.3 examined the correlations between dietary fatty acid intakes and plasma phospholipid fatty acid levels, and the correlation coefficient was low to moderately high levels. But dietary fatty acid intakes were significantly associated with plasma phospholipid fatty acid status, including omega-3 and omega-6 PUFAs, and health promotion by appropriate food consumption and monitoring plasma levels can be recommended. Finally, plasma omega-6 and omega-3 concentrations, expressed by mmol/L or μg/mL, have not been popular in the past epidemiological studies. Serum low-density lipoprotein cholesterol (LDL-C) was usually expressed by absolute value, instead of LDL-C/total cholesterol ratio, and the absolute values of omega-6 and omega-3 PUFAs should also be used to examine the association with cancer incidence. Tomoyuki Kawada: Conceptualization; writing – original draft; writing – review and editing; investigation. The author declares no conflicts of interest.