L-lysine is an amino acid, a building block of proteins, that the human body cannot produce. It must be obtained through diet or supplementation, found in foods like meat, fish, dairy, and eggs. While commonly used for general health, such as managing cold sores, any supplement use during pregnancy requires caution.
Safety Profile of L-Lysine During Pregnancy
The scientific understanding of L-lysine’s safety during pregnancy is limited. Extensive, high-quality human studies, including randomized, double-blind trials, have not been conducted. This lack of rigorous research means there is insufficient reliable information to definitively state whether L-lysine supplements are safe for use during pregnancy or breastfeeding.
While L-lysine is naturally present in a balanced diet, supplemental forms demand greater scrutiny. Over-the-counter L-lysine supplements have not been approved for use in pregnancy. A general principle of caution applies to most supplements during pregnancy due to insufficient data on their effects on the developing fetus.
One concern is that L-lysine competes with arginine for transport into cells. Arginine is important for endothelial function and placental development; its deficiency has been linked to pre-eclampsia. Some observations suggest a potential link between L-lysine supplementation during pregnancy and outcomes like small for gestational age (SGA) babies, hypertension, and preeclampsia, though a direct causal relationship is not established.
A systematic review on L-lysine supplementation in healthy human subjects found adverse events were mainly gastrointestinal symptoms, with a provisional no-observed-adverse-effect level at 6.0 grams per day. However, this review did not focus on pregnant populations, and the safety profile in this sensitive group remains largely unstudied. Due to limited research, pregnant individuals are generally advised to avoid L-lysine supplements.
Guidance for Expectant Mothers
Pregnant individuals considering L-lysine or any other supplement must consult a healthcare provider, such as an OB/GYN or midwife. A doctor can assess individual health conditions, review existing medications, and identify potential interactions that could affect pregnancy. Unlike prescription drugs, dietary supplements are not reviewed by the U.S. Food and Drug Administration (FDA) for safety and effectiveness, and they may contain contaminants or have inconsistent ingredient quality.
A healthcare provider offers personalized advice based on individual needs and medical history. For common reasons L-lysine is considered, such as managing cold sores, safer alternatives are available and should be discussed with a doctor. For instance, antiviral medications like acyclovir cream or tablets are considered safe at all stages of pregnancy for treating cold sores. Patches that act locally without active ingredients are also safe options.
While L-lysine is sometimes considered for cold sores during pregnancy and breastfeeding, there is little scientific data to support its use for this purpose. The American College of Obstetricians and Gynecologists (ACOG) and the Academy of Nutrition and Dietetics recommend that pregnant women take a daily prenatal vitamin, folic acid, and vitamin D supplements to meet nutritional needs and prevent certain developmental abnormalities. Any other supplement should be approached with caution and only under medical oversight.