Links to Zinc: Nutrition Expert Finds Tie Between Trace Mineral, Birth Weights

By Michael Washington

When Dr. Yasmin Neggers began her latest study of how zinc levels in expectant mothers affect birth weight – a key factor in infant mortality – she hoped for a significant outcome.

Imagine her and her associates’ surprise upon finding that low blood zinc levels in expectant mothers increased the risk of low birth weight by approximately eight times.

These results may be significant for states like Alabama where infant mortality rates are above the national average. Some of this state’s counties have infant mortality rates higher than that of some third-world countries where residents’ overall health status is poor.

Zinc, a trace mineral found naturally in the body, was known to aid in cell development and growth. Higher levels of zinc are promoted by a healthy, balanced diet including meats, dairy and whole grains. However, there was little research that directly linked zinc to specific growth outcomes, and scientists are still debating the healthy levels of trace elements needed in the human body.

“At the time that I began working on my dissertation, research on zinc was just emerging yet no one knew for sure how essential it was for humans,” says Neggers, professor of human nutrition and hospitality management at The University of Alabama. “The link between zinc and cell growth was in the news, some research was already done that implied zinc was maybe linked to low birth weight, and I knew that low birth weight in Alabama was a big problem.”

The Problem

According to the Journal of the American Medical Association, a baby has low birth weight when he or she weighs less than 2,500 grams or 5 pounds, 8 ounces. One in 14 babies born in the U.S. is affected, and Alabama is above the national rate with about one in ten cases. Those numbers have not significantly declined in Alabama since the mid-1980s, especially among African-American women and women of low-income backgrounds.

Low birth weight babies are at increased risk for serious health problems, including underdeveloped lungs and death. While recent advances in newborn medical care have greatly reduced the number of low birth weight deaths, a small percentage of survivors develop mental retardation, learning problems, cerebral palsy, and vision and hearing loss.

So Neggers began searching, in partnership with Drs. Robert Goldenberg and William Andrews of the University of Alabama at Birmingham department of obstetrics and gynecology, for a tangible link between the cell-building trace mineral and birth weight.

The Research

The research conducted by Neggers and her UAB associates came following a series of previous studies the UA College of Human Environmental Sciences faculty member had conducted. In the latest effort, the researchers focused on the populations that seemed most affected by low birth weight.

“Women of low socio-economic status are more likely to have lower levels of zinc intake and zinc blood levels,” says Neggers. “Also, it is unclear why, but African-Americans tend to have lower birth weights than Caucasians. So, we looked in populations where low birth weight was more common and low intake of zinc might also be common.”

The participants of the study were expectant mothers visiting the women’s health clinic at UAB. They came from the Black Belt of Alabama and the areas around UAB.

“The women visiting that clinic were from low-income backgrounds and had no other healthcare. This made following our subjects convenient since they attended this clinic throughout pregnancy,” says Neggers.

In previous work, Neggers found a correlation between blood zinc levels and birth weight while analyzing blood taken from women throughout pregnancy. The latest results not only supported the original assumption, but extended it.

“We separated the blood zinc levels into four quartiles, lowest to highest. We were surprised to find that after adjusting for other factors associated with low birth weight, women having low blood zinc levels, compared to women with normal zinc levels, were eight times more likely to give birth to low birth weight babies. We expected that maybe the prevalence of low birth weight would be somewhat higher, but not eight times,” says Neggers. “We became more interested since low birth weight is a major predictor of infant mortality.”

For the current study, Neggers and her associates conducted a clinical trial to find if supplementing zinc affects birth weight.

“It was a double blind trial. We gave 30 mg of supplemental zinc to indigent women. The groups were randomized with the only variable being one group got minerals and vitamins, and the other group got minerals and vitamins, plus a zinc supplement. We then followed them for nine months, each woman returning to the clinic four times throughout pregnancy. We measured their blood levels and dietary intake, and kept account of whatever else they were doing,” says Neggers. “We found that there were significant differences in their birth weight.”

All other factors in both groups – including age, race, socio-economic status and dietary zinc levels – were the same. The only difference in the groups was the addition of a zinc supplement. The group that received the zinc supplement gave birth to babies 150 grams (about 5.3 ounces) heavier than the babies of the group not receiving the supplement.

“That difference may not seem like a lot, but having low birth weight is weighing less than 2,500 grams (5 pounds, 8 ounces),” says Neggers. “For small infants, 150 grams really make a difference. We also found, interestingly, that thinner women with low blood zinc levels who took the zinc supplement had a better result – up to 250 grams increase in the baby’s weight. A 10 percent increase is very good.”

The Next Step

Fortunately, it has become standard practice in the U.S. to advise expectant mothers of the importance in taking prenatal vitamins. Neggers says taking the vitamins and minerals recommended by a doctor will adequately cover the needed dosage to encourage healthier birth weights. However, not everyone has access, whether those limitations involve finances, insurance coverage or lack of knowledge.

“This research is of most importance to those Alabama counties and other countries where zinc intake is low to begin with and women are not given multivitamins during pregnancy,” says Neggers. “But if you are at high risk of having low zinc levels due to a factor like poor diet, then taking a supplement is very important.”