For those hoping to conceive, a new study coming out of Pennsylvania State University has found that zinc deficiency may factor into fertility struggles.
The researchers found that zinc deficiency can negatively affect the early stages of egg development.
This means it is more difficult for the egg cells to divide and be fertilised, and could then affect future fertility months.
The study, which will be presented at the American Physiological Society annual meeting at Experimental Biology 2018 in San Diego, looked at egg cells, or oocytes, and their maturation.
Our ovaries are made up structures called follicles, and women are born with about two million follicles. Each follicle consists of a single oocyte surrounded by support cells (somatic cells).
"More and more evidence is accumulating that zinc is a key player in oocyte development," lead author James Hester told Science Daily.
Hester and his fellow researchers focused on follicles that are still growing, known as preantral follicles.
He wrote, "Fertility research and treatment has primarily focused on the largest class of follicles (antral follicles), which are capable of ovulating in response to hormonal signals from the pituitary gland.
"In contrast, our study examines smaller preantral follicles, which are still growing and don't respond to the ovulatory signal yet. In humans, preantral follicles have to keep growing for about 90 days before they are ready to ovulate.
"Previous studies showed that zinc levels are critical in the antral follicle, but no one had tested the effect of zinc deficiency on preantral follicle growth."
Their research was conducted using preantral follicles collected from mice. When they compared eggs matured with zinc deficiency compared to those with normal zinc levels, they found that it led to smaller egg cells early in development.
Zinc deficiency in the preantral follicles also disrupted the growth of cells in culture, caused issues in the development of somatic cells, and hindered its ability to divide (meiosis). Meiosis is a necessary step for successful fertilisation.
"Animal studies have consistently shown a zinc requirement for oocytes during meiotic division, fertilization and embryo development," Hester noted, "Our new research shows that zinc plays a role in oocyte growth at an earlier stage than previously investigated, during development and before division."
"Otherwise, it doesn't matter what the conditions are during ovulation," he continued, "Interestingly, the oocytes commonly used for [in vitro fertilization] are collected from antral follicles, so any effects from preantral development have already occurred."
The World Health Organisation estimates that 17 percent of the world's population is zinc deficient (and that figure may not even include people with marginal zinc deficiency).
There are a number of groups at risk of being zinc deficient, including people with Crohn's disease, irritable bowel syndrome, gastrointestinal disorders, and liver disease. As well, women with dietary restrictions, like vegans or vegetarians, may be at risk if they don't take a zinc supplement.