Increasing levels of industrially derived trans fatty acids in European erythrocytes.

Combined erythrocyte levels of C18:1t, 18:2tc, 18:2tt, and 18:2ct (or industrially-produced trans fatty acids, IP-TFA) > 1.04% are associated with increased mortality, as compared with lower levels. In the United States, mean erythrocyte levels of IP-TFA declined from 2009 to 2016, with a parallel decline in mortality. In Europe, in 2014 and 2015, only 1.3% of erythrocyte samples had levels of IP-TFA > 1.04%. However, recently IP-TFA levels increased, driven only by increases of 18:1t. In 2024, in 2.12% of 20,510 samples, IP-TFA were >1.04%; in 2025, in 4.47% of 27,834 samples; in January - June 2026, in 7.21% of 18,577 samples (p for trend <0.001). Since levels of C16:1n7t, a marker of dairy intake like vaccenic acid (C18:1t-11), remained constant from 2020 to 2026, we assume the increase to be driven mainly by elaidic acid (C18:1t-9), detected, e.g., in adulterated olive oil. This increase is likely to be associated with increased mortality in Europe.