The n-3 index has been proposed as a risk factor for CVD endpoints. However, the association of the O3I defined with different cut-offs and cardiometabolic risk factors has been less studied. This study aimed to investigate the association between two cut-off points of the O3I and cardiometabolic risk factors in Brazilian and Puerto Rican adults. This cross-sectional analysis included 249 Brazilians and 1261 Puerto Ricans, aged 45–75 years. Fatty acids composition was quantified in erythrocyte membranes using GC with a flame ionisation detector. The O3I was categorised as ≤ 4 % (low), > 4–8 % (intermediate) and ≥ 8 % (desirable), and as ≤ 4 % (very low), > 4–6 % (low), > 6–8 % (moderate) and > 8 % (high) in the second cut-off classification. Serum lipids, waist circumference and insulin resistance were measured from standardised protocols. Multivariable-adjusted linear models tested the association between the O3I and cardiometabolic factors. Brazilians had a mean (sd) O3I of 4·65 % (1·19 %) v. 4·43 % (1·14 %) in Puerto Ricans (P = 0·033), with only 1·6 % of Brazilians and 1·2 % of Puerto Ricans presenting a desirable/high O3I. The O3I, as continuous or for > 4 % (v. ≤ 4 %), was inversely associated with TAG, VLDL and TAG/HDL-cholesterol ratio in Puerto Ricans. In Brazilians, an O3I > 6 % (v. ≤ 6 %) was associated with higher total cholesterol, LDL-cholesterol and non-HDL-cholesterol. Both populations presented O3I below the desirable levels, and the magnitude and direction of associations with cardiometabolic factors varied by study and cut-offs, reinforcing the importance of expanding these investigations to more diverse populations.

n-3 index, the erythrocyte proportion of the EPA + DHA fatty acids is a clinical marker of age-related disease risk. It is unclear whether regular intake of α-linolenic acid (ALA), a plant-derived n-3 polyunsaturated fatty acid, raises n-3 index in older adults. Of the 356 participants at the Loma Linda, CA centre from the original study, a randomly selected subset (n 192) was included for this secondary analysis (mostly Caucasian women, mean age 69 years). Participants were assigned to either the walnut (15 % of daily energy from walnuts) or the control group (usual diet, no walnuts) for 2 years. Erythrocyte fatty acids were determined at baseline and 1-year following intervention. No differences were observed for erythrocyte EPA, but erythrocyte DHA decreased albeit modestly in the walnut group (–0·125 %) and slightly improved in the control group (0·17 %). The change in n-3 index between the walnut and control groups was significantly different only among fish consumers (those who ate fish ≥ once/month). Longitudinal analyses combining both groups showed significant inverse association between the 1-year changes of the n-3 index and fasting plasma TAG (ß = −10), total cholesterol (ß = −5·59) and plasma glucose (ß = −0·27). Consuming ALA-rich walnuts failed to improve n-3 index in elders. A direct source of EPA/DHA may be needed to achieve desirable n-3 index, as it is inversely associated with cardiometabolic risk. Nevertheless, incorporating walnuts as part of heart healthy diets is still encouraged.

The association between n-3 PUFA intake and type 2 diabetes (T2D) is unclear, and studies relating objective biomarkers of n-3 PUFA consumption to diabetic status remain limited. The aim of this study was to determine whether erythrocyte n-3 PUFA levels (n-3 index; n-3I) are associated with T2D in a cohort of older adults (n 608). To achieve this, the n-3I (erythrocyte %EPA+%DHA) was determined by GC and associated with fasting blood glucose; HbA1c; and plasma insulin. Insulin resistance (IR) was assessed using the homeostatic model assessment of insulin resistance (HOMA--IR). OR for T2D were calculated for each quartile of n-3I. In all, eighty-two type 2 diabetic (46·3 % female; 76·7 (sd 5·9) years) and 466 non-diabetic (57·9 % female; 77·8 (sd 7·1) years) individuals were included in the analysis. In overweight/obese (BMI≥27 kg/m2), the prevalence of T2D decreased across ascending n-3I quartiles: 1·0 (reference), 0·82 (95 % CI 0·31, 2·18), 0·56 (95 % CI 0·21, 1·52) and 0·22 (95 % CI 0·06, 0·82) (P trend=0·015). A similar but non-significant trend was seen in overweight men. After adjusting for BMI, no associations were found between n-3I and fasting blood glucose, HbA1c, insulin or HOMA-IR. In conclusion, higher erythrocyte n-3 PUFA status may be protective against the development of T2D in overweight women. Further research is warranted to determine whether dietary interventions that improve n-3 PUFA status can improve measures of IR, and to further elucidate sex-dependent differences.