Molybdenum

Chemical Properties#

Transition metal (Group 6); biologically active as molybdenum (Mo)(IV), molybdenum(vanadium (V)), and molybdenum(VI).

Functions exclusively as part of the molybdenum cofactor (Moco), a pterin-based organic molecule that coordinates molybdenum and inserts it into the active sites of molybdoenzymes.

Moco deficiency is a rare but lethal inborn error of metabolism causing seizures, neurodegeneration, and early death. Dietary requirement is low: RDA of 45 ug/day for adults; UL of 2 mg/day.

Dietary#

Legumes, grains, nuts, and leafy vegetables are the primary dietary sources. Soil molybdenum content varies geographically, affecting plant molybdenum (Mo) concentrations.

Baby food jars from Spain contained molybdenum at 4 times higher than maximum recommended values, alongside elevated manganese.^{[3]Baby Food Jars as a Dietary Source of Essential (K, Na, Ca, Mg, Fe, Zn, Cu, Co, Mo, Mn) and Toxic Elements (Al, Cd, Pb, B, Ba, V, Sr, Li, Ni)Gonzalez-Suarez S, Paz-Montelongo S, Niebla-Canelo D et al. · 2022Open reference 3 ↓}

Breast Cancer—Inverse Association#

The Sister Study, the largest prospective study of metals and breast cancer (1,495 cases, 1,605 subcohort), found that molybdenum (Mo) was the only metal with a significant inverse association with breast cancer risk.^{[2]Metals and Breast Cancer Risk: A Prospective Study Using Toenail BiomarkersNiehoff NM, O'Brien KM, Keil AP et al. · 2021Open reference 2 ↓}

Third tertile vs. first: HR = 0.82 (95% CI: 0.67, 1.00) for overall breast cancer. Stronger inverse association for ER-negative breast cancer (HR = 0.57, 95% CI: 0.38, 0.88). Toenail molybdenum reflects 6-12 months of exposure, providing longer-term assessment than blood/urine.

Mechanism: potentially related to molybdenum's role as cofactor for enzymes that break down toxic sulfites and other xenobiotics.^{[2]Metals and Breast Cancer Risk: A Prospective Study Using Toenail BiomarkersNiehoff NM, O'Brien KM, Keil AP et al. · 2021Open reference 2 ↓}

PCOS—Lower Levels#

The first study to examine molybdenum (Mo) in PCOS found significantly lower levels in affected women.^{[1]Association of Trace Elements with Polycystic Ovary Syndrome in Women -- A Case-Control StudySmovrsnik T, Pinter B, Horvat M et al. · 2025Open reference 1 ↓}

molybdenum whole blood: PCOS 0.60 vs control 0.71 ug/L (p = 0.024). molybdenum serum: PCOS 0.85 vs control 1.00 ug/L (p = 0.011). Negative correlation between molybdenum and LH levels in PCOS women, suggesting a potential protective role of molybdenum in reducing androgen levels.

Differences were no longer statistically significant after adjusting for age, BMI, and hematocrit, indicating possible confounding.

Dietary predictors: cereals and boiled vegetables were important predictors of molybdenum levels; copper (Cu)-molybdenum antagonism (excess copper decreases molybdenum absorption by forming non-absorbable copper-molybdenum complexes in the GI tract) may be relevant given elevated Copper in PCOS.^{[1]Association of Trace Elements with Polycystic Ovary Syndrome in Women -- A Case-Control StudySmovrsnik T, Pinter B, Horvat M et al. · 2025Open reference 1 ↓}

molybdenum positively correlated with AST, ALT, and urinary urobilinogen in PCOS, suggesting associations with liver function.^{[1]Association of Trace Elements with Polycystic Ovary Syndrome in Women -- A Case-Control StudySmovrsnik T, Pinter B, Horvat M et al. · 2025Open reference 1 ↓}

Interactions with Other Metals#

Copper-molybdenum antagonism: Excess copper (Cu) decreases molybdenum (Mo) absorption by forming insoluble copper-molybdenum-S complexes (thiomolybdates) in the GI tract.

This is well established in ruminant nutrition ("swayback" in sheep from copper deficiency induced by high-molybdenum pastures) and may be relevant in human PCOS where copper is elevated and molybdenum is low.^{[1]Association of Trace Elements with Polycystic Ovary Syndrome in Women -- A Case-Control StudySmovrsnik T, Pinter B, Horvat M et al. · 2025Open reference 1 ↓}

Iron: molybdenum and iron (Fe) share some transport pathways; Moco synthesis requires iron-sulfur cluster biogenesis.

molybdenum is classified as a toxic element in some food safety contexts (baby food studies) despite being essential.^{[3]Baby Food Jars as a Dietary Source of Essential (K, Na, Ca, Mg, Fe, Zn, Cu, Co, Mo, Mn) and Toxic Elements (Al, Cd, Pb, B, Ba, V, Sr, Li, Ni)Gonzalez-Suarez S, Paz-Montelongo S, Niebla-Canelo D et al. · 2022Open reference 3 ↓}