Omega-3 index levels and associated factors in a middle-aged French population: the MONA LISA-NUT Study

The omega-3 index (the summed percentage content of eicosapentaenoic and docosahexaenoic acids in red blood cells) is associated with a lower risk of fatal coronary heart disease and sudden cardiac death. We aimed to determine which socio-demographic, behavioural or clinical factors are independently associated with the omega-3 index and the extent to which seafood consumption mediates the index's association with socio-economic status (SES).

As part of the cross-sectional MONA LISA-NUT survey (2005-2007), gas chromatography was used to analyse the red blood cell fatty acid composition in 503 French subjects aged 35-64 years. Dietary data were collected by trained dieticians via a validated food frequency questionnaire and a prospective 3-day food record. Risk factors were estimated with standardised measurements and questionnaires. SES was assessed through the self-reported educational and income tax levels.

The mean ± s.d. omega-3 index was 6.02 ± 1.75%. In the best parsimonious predictive model (which explained 32% of the variability in the omega-3 index), age, educational level and seafood servings were significantly and positively associated with the index. In contrast, waist circumference and smoking were inversely associated with the index. In a mediation analysis that took account of all these factors, seafood servings explained about 40% of the association between educational level and the omega-3 index. Similar results were obtained for the income tax level.

The inverse association between SES and omega-3 index is largely explained (40%) by an insufficient seafood intake. It remains to be seen which other factors mediate this association.