Dietary ALA intake may lower risks of all-cause, CVD, CHD mortality

Dietary intake of alpha linolenic acid (ALA) appears to reduce the risk of mortality from all causes, cardiovascular disease (CVD), and coronary heart disease (CHD) but may slightly increase the risk of cancer mortality, according to a systematic review and meta-analysis. Moreover, an association exists between higher blood levels of ALA and a lower risk of all-cause and CHD mortality.

“We found a significant inverse association between blood levels of ALA and risk of all-cause mortality,” the researchers said. “Additionally, each 1-standard deviation (SD) increment in blood and total plasma or serum levels of ALA was associated with a reduced risk of CHD and CVD mortality, respectively.”

Prospective cohort studies reporting the risk estimates for death from all causes, CVD, and cancer were searched from the databases of PubMed, Scopus, ISI Web of Science, and Google Scholar until 30 April 2021. The researchers calculated summary relative risks (RRs) and 95 percent confidence intervals (CIs) for the highest vs lowest categories of ALA intake using random and fixed effects models.

Finally, the dose-response associations between ALA intake and mortality were evaluated by conducting linear and nonlinear dose-response analyses.

Forty-one articles from prospective cohort studies, involving 1,197,564 participants, met the eligibility criteria of this study. A total of 198,113 deaths from all causes, 62,773 from CVD, and 65,954 from cancer were recorded during follow-up (range, 2–32 years).

High vs low intake of ALA significantly correlated with a reduced risk of deaths from all causes (pooled RR, 0.90, 95 percent CI, 0.83–0.97; I², 77.8 percent; n=15 studies), CVD (pooled RR, 0.92, 95 percent CI, 0.86–0.99; I², 48.2 percent; n=16), and CHD (pooled RR, 0.89, 95 percent CI, 0.81–0.97; I², 5.6 percent; n=9), and a marginally higher risk of cancer death (pooled RR, 1.06, 95 percent CI, 1.02–1.11; I², 3.8 percent; n=10). [BMJ 2021;375:n2213]

Dose-response analysis revealed that a 1-g/day increase in ALA intake (equivalent to 1 tbsp of canola oil or 0.5 oz of walnut) could result in a 5-percent lower risk of all-cause (pooled RR, 0.95, 95 percent CI, 0.91–0.99; I², 76.2 percent; n=12) and CVD mortality (pooled RR, 0.95, 95 percent CI, 0.91–0.98; I², 30.7 percent; n=14).

Of note, a significant inverse association was observed between blood levels of ALA and the risk of all-cause mortality (pooled RR, 0.95, 95 percent CI, 0.90–0.99; I², 8.2 percent; n=26). In addition, each 1-SD increase in blood concentrations of ALA correlated with a reduced risk of CHD mortality (pooled RR, 0.92, 95 percent CI, 0.86–0.98; I², 37.1 percent; n=14).

“In the current meta-analysis, higher tissue levels of ALA were associated with a reduced risk of all-cause mortality, whereas this was not significant for CVD and CHD mortality,” the researchers said. “This might be explained by ALA being measured in different tissues.”

When the analysis was confined to studies considering blood ALA, specifically total plasma or serum ALA, the nonsignificant inverse relationships between ALA and mortality due to CVD and CHD became significant.

“It seems that blood levels of ALA are objective biomarkers of circulating levels of ALA over the past 1–2 months that reflect diet together with the metabolism of dietary ALA. Therefore, findings from ALA blood levels compared with adipose tissue levels are more consistent with the findings from dietary ALA intake,” the researchers said. [Br J Nutr 2014;112:1206-1213]

“Further studies should examine the association between ALA and a wider range of causes of death to provide a more comprehensive assessment of the potential health effects of ALA as well as to examine whether specific foods rich in ALA are differentially associated with mortality from cancer and other causes,” they added.