A diet low in manganese may increase the risk for anovulation, or failure of the ovary to release an egg during a menstrual cycle. Approximately every 28 days, the female body prepares for pregnancy. About halfway through the cycle, the ovary will release an egg in response to hormonal changes. Disruptions in this process can result in infertility.

The BioCycle Study, completed at the University at Buffalo, was initiated to better understand the impact of diet and lifestyle on reproductive hormones and menstrual cycle abnormalities, including anovulation. The study assessed 259 healthy, regularly menstruating women over the course of two menstrual cycles. Data collected provide insight on health history and physical activity. Blood samples collected from participants at eight specific phases of the menstrual cycle are used to measure hormone levels and detect irregularities in ovulation. In addition, the collection of dietary data promotes evaluation of nutrient intake and reproductive health outcomes.

Researchers at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) assessed the impact of dietary mineral intake on anovulation using data from the BioCycle Study. They found that a diet low in manganese, in reference to the recommended adequate intake (1.8mg/day for adult women), is associated with an increase in risk for anovulation.

How does this affect fertility?

Increasing intake of manganese is reasonable given that it is abundant in several readily available foods including teas, nuts, legumes, and whole grains But, before making dietary adjustments to improve fertility, the implications of these findings should be considered within the context of study design. In this case, anovulation was defined as sporadic, in that ovulation was only assessed over the course of two cycles and previous menstrual cycles occurred regularly. Consistent anovulation is a common cause of infertility, whereas intermittent anovulation is thought to have minimal impact on fertility, as menstrual cycles occurring before and after are believed to be healthy. However, a role for dietary manganese in fertility should not be ruled out as women with one sporadic anovulation have abnormal hormone profiles during preceding and future ovulatory cycles. This suggests ovarian dysfunction that may impact fertility.

Why does a diet low in manganese impair ovulation?

The exact function of manganese in human reproduction is not fully understood; however, studies rat studies indicate that the essential micronutrient may impact ovulation through its effects on the brain. Manganese accumulates in the hypothalamus, a region of the brain that regulates levels of reproductive hormones. Injection of manganese into the brain of prepubertal female rats increases levels of luteinizing hormone releasing hormone (LHRH), a reproductive hormone critical for ovulation.

Direct administration to the brain significantly differs from dietary intake of manganese; therefore further studies are required to determine the impact of manganese obtained from the diet. In addition, only a portion of manganese from the diet is absorbed, while the rest is excreted. Therefore, deficiency may be better reflected in manganese serum concentrations rather than dietary assessment. Furthermore, the body stores manganese in tissues including bone, liver, kidney, and pancreas. This suggests that a short-term dietary deficiency may not affect the overall balance of manganese in the body.

Nevertheless, observations on the association of dietary mineral intake and anovulation from the BioCycle Study are critical in stimulating further investigation into the impact of manganese on fertility.