Toxicity of oxidized fish oil in pregnancy: a dose-response study in rats

Fish oil (FO) supplements are consumed during pregnancy to increase dietary omega-3. However, FO is often oxidized past recommended limits. In rats, a large dose of highly oxidized FO substantially increased newborn mortality, but the effects of human-relevant doses of less oxidized oil are unknown. A dose-response study in rats was conducted to estimate the safe level of oxidation during pregnancy. Sprague-Dawley rat dams were mated, then individually housed and provided with a gel treatment on each day of pregnancy. Treatment groups differed only in the FO content of the gel; control (no oil), PV5, PV10, and PV40 [0.05 mL of FO oxidized to a peroxide value (PV) of 5, 10, or 40 meq/kg], or PV40(1 mL) (1 mL of PV40). A subset of dams was culled on gestational day 20 to enable sampling, and the remainder were allowed to give birth. Newborn mortality was recorded. Offspring were sampled on postnatal days 2 and 21, and dams on day 21. There were no signs of unwellness during pregnancy. However, there was markedly increased neonatal mortality affecting the PV40(1 mL) (12.8%) and PV40 (6.3%) groups, but not the control, PV5, or PV10 groups (1%-1.4%). Dietary-oxidized FO altered the expression of placental genes involved in antioxidant pathways and the production of free radicals. Highly oxidized FO was toxic in rat pregnancy leading to a marked increase in mortality even at a human-relevant dose. We observed no toxic effects of FOs with PV <= 10 meq/kg, suggesting that this is an appropriate maximum limit.

Automated summary

A study found that fish oil supplements consumed during pregnancy can increase dietary omega-3 intake. However, fish oil is often oxidized beyond recommended limits, leading to negative effects on fetal health. Through experiments with rats, it was discovered that highly oxidized fish oil can increase mortality rates during pregnancy, while fish oil with lower levels of oxidation does not have the same impact. Additionally, dietary-oxidized fish oil also alters the expression of placental genes.