The Recommended Dietary Allowance (RDA) for adult men and women is 45 μg/day. The average dietary intake of molybdenum by adult men and women is 109 and 76 μg/day, respectively. The Tolerable Upper Intake Level (UL) is 2 mg/day, a level based on impaired reproduction and growth in animals.
Too Much Can Cause Serious Side Effects
As with most vitamins and minerals, there is no advantage to taking more than the recommended amount of molybdenum.
In fact, doing so can harm your health.
The tolerable upper intake level (UL) is the highest daily intake of a nutrient that is unlikely to cause harm for almost all people. It is not recommended to regularly exceed it.
The UL for molybdenum is 2,000 micrograms (mcg) per day (18).
Molybdenum toxicity is rare and studies in humans are limited. However, in animals, very high levels have been linked to reduced growth, kidney failure, infertility and diarrhea (19).
On rare occasions, molybdenum supplements have caused serious side effects in humans, even when the doses were well within the UL.
In one case, a man consumed 300–800 mcg per day over 18 days. He developed seizures, hallucinations and permanent brain damage (20).
High molybdenum intake has also been linked to a number of other conditions.
Too much molybdenum can cause a buildup of uric acid due to the action of the enzyme xanthine oxidase.
A group of Armenian people who each consumed 10,000–15,000 mcg a day, which is 5–7 times the UL, reported gout-like symptoms (19).
Gout occurs when there are high levels of uric acid in the blood, which causes tiny crystals to form around the joints, leading to pain and swelling.
Poor Bone Health
Studies have shown that a high intake of molybdenum could possibly cause decreased bone growth and bone mineral density (BMD).
Currently, there are no controlled studies in humans. However, an observational study of 1,496 people found interesting results.
It found that as molybdenum intake levels increased, lumbar spine BMD appeared to decrease in women over the age of 50 (21).
Controlled studies in animals have supported these findings.
In one study, rats were fed high amounts of molybdenum. As their intake increased, their bone growth decreased (22).
In a similar study in ducks, high intakes of molybdenum were associated with damage to their foot bones (23).
Research has also shown an association between high molybdenum intake and reproductive difficulties.
An observational study including 219 men recruited through fertility clinics showed a significant relationship between increased molybdenum in the blood and decreased sperm count and quality (24).
Another study also found that increased molybdenum in the blood was linked to decreased testosterone levels. When combined with low zinc levels, it was linked with a whopping 37% reduction in testosterone levels (25).
Controlled studies in animals have also supported this link.
In rats, high intakes have been linked to decreased fertility, growth failure of offspring and sperm abnormalities (26, 27, 28).
Although the studies raise many questions, more research is needed.