Increasing iron intake does not improve the chances of conception

By Dr. Liji Thomas, MDJun 11 2019

Researchers studying the relationship between human conception and iron intake from both animal and plant sources have found that women who are trying to conceive do not benefit from increasing iron intake.

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Infertility is a source of significant mental and emotional distress, and rising healthcare costs, putting a heavy load on both patients and healthcare providers. Many factors which improve fertility have been studied, including dietary intake of iron and vitamins. However, it is still not clear as to how iron affects fertility.

A previous study carried out among nurses in the US found that taking iron in the form of plant-based foods and as iron supplements produced a 40% improvement in infertility related to ovulatory factors. The current research was focused on finding the extent to which iron intake affected fertility in women.

The researchers at Boston University School of Public Health (BUSPH) used data from two databases on women who planned to conceive. The data was from prospective cohorts, which meant that the outcomes were not known at the time the study began.

One was the PRESTO study, based at BUSPH, and covered almost 3000 women who were trying to become pregnant. The other was the Snart Foraeldre study based in Denmark, which had almost 1700 participants. Both studies included women whose diet contained non-heme iron (from plants and iron supplements), as well as animal meat which contains heme iron.

The fecundability rate was calculated for each group based on this data. The FR refers to the probability of conception per at-risk cycle comparing the first to the second cohort. An at-risk cycle is a menstrual cycle during which the woman tries to conceive. An FR of less than 1 indicates a reduced chance of conception or a longer time to conceive.

The women were studied for iron intake in terms of their pregnancy rates until one of the following outcomes occurred: pregnancy or a censoring event, at which they were not eligible for the study. This included intake into a fertility treatment program, cessation of conception attempts, withdrawal from the study, or loss to follow up. Women were also not followed up after 12 cycles of trying to conceive, since at this point fertility treatment is typically initiated.

The women answered questionnaires about their dietary intake of iron-containing foods, both animal and plant-based, as well as the use of iron-containing supplements. This was used to estimate how much heme and non-heme iron they took, on average, over the study period.

Other data about menstrual cycle dates was used to estimate how many at-risk cycles each woman contributed to the assessment. The results ruled out any significant contribution of heme iron intake to pregnancy rates in either group of women.

Take a multivitamin, not an iron supplement

For non-heme iron, women in the PRESTO study who took over 11 mg daily had an FR of 1.11 (compared to the cohort who took less than 9 mg daily). Those who took supplements containing iron had an FR of 1.01.

In the Snart Foraeldre study, the FR for women consuming non-heme iron, and for women on iron-containing supplements, was 1.01 and 1.19 respectively. These results are not significant enough to say that iron intake increases the likelihood of pregnancy, say the researchers.

However, the association between iron intake from non-heme sources, and from iron supplements, was stronger for women who had heavy menstrual cycles or more frequent menstruation due to shorter cycle length. This also applied to women who had previously given birth to one or more children. This suggests that iron may be beneficial for women who experience heavy menstrual cycles, but further research will be needed to confirm this hypothesis.

The authors conclude that dietary intake of iron does not significantly improve conception rates. However, women who are at risk for iron deficiency due to heavy periods or short intermenstrual intervals could benefit from a higher intake of dietary iron intake. In addition, women in North America, but not Denmark, appeared to benefit more from iron supplement use.

For the average pregnancy planner, it is probably wise to take a preconception multivitamin, but more for the folic acid than for the iron content. If you have extremely heavy menstrual cycles, it might be a good idea to have your iron status checked by your healthcare provider.”

Elizabeth Hatch, Senior Author