Study: Eating Fish During Pregnancy Protects Against Mercury Toxicity

Is it safe to eat fish during pregnancy? You may have been told to avoid it, or to only eat limited amounts or certain types, but a recent study indicates that those restrictions may not be necessary.

The study in “NeuroToxicology” finds that the mercury levels in fish aren’t likely to have a negative effect on your child if you eat fish, suggesting that consuming fish can be protective against mercury exposure.

For the most part, current advice on mercury toxicity in pregnancy warns pregnant women not to eat certain kinds of fish known to have high levels of the metal. The U.S. Food and Drug Administration (FDA) tells expecting mothers to avoid consuming large fish including swordfish, bigeye tuna, king mackerel, and certain other types of fish.

But guidance can be confusing, as other organizations continue to promote fish consumption during pregnancy: The Scientific Advisory Committee to the 2020-2025 Dietary Guidelines for Americans publicly acknowledged that fish have “predominantly beneficial associations” and “few detrimental associations.”

An analysis of more than 4,131 pregnant mothers who had mercury in their bodies showed that it didn’t cause adverse effects in their children—so long as the mother ate fish.

“If she did not eat fish, then there was some evidence that her mercury level could have a harmful effect on the child. This could be because of the benefits from the mix of essential nutrients that fish provides, including long-chain fatty acids, iodine, vitamin D and selenium,” says Caroline Taylor, PhD, co-author of the study and a senior research fellow at Bristol Medical School at University of Bristol.

Jean Golding, PhD, a co-author and emeritus professor at University of Bristol, tells Motherly she was intrigued that there was a strong preventative effect of adverse effects when the mercury came from fish. But she wasn’t surprised that eating fish during pregnancy was beneficial to the child.

Should you avoid fish during pregnancy?

Worried that certain fish still need to stay off the menu while you’re waiting for your bundle of joy to arrive? The researchers say it didn’t seem to matter what types of fish the women ate—the nutrients found in fish could protect the mother from the mercury content.

Other studies have explored the topic (many saying fish is totally OK), but this study was unique in that it looked at populations with contrasting mercury levels, then followed up on the children during childhood. One population was in the Seychelles off East Africa, where most pregnant women eat fish regularly, and prenatal mercury levels are more than 10 times the amount seen in the US. The second study used data from a population in England, where fish isn’t as common in prenatal diets. The researchers found that increased mercury levels were not associated with adverse outcomes in children born to mothers who ate fish.

We know that there are benefits to eating fish in pregnancy—namely, the omega-3 fatty acids can boost brain and eye development. But the warnings issued have caused some women to avoid fish completely while they are pregnant.

New guidelines for fish during pregnancy on the way?

That’s why the advice needs to be changed, Dr. Golding says.

“It is important that advisories from health professionals revise their advice warning against eating certain species of fish,” Dr. Golding says. “There is no evidence of harm from these fish, but there is evidence from different countries that such advice can cause confusion in pregnant women.”

Dr. Golding says guidance should advise women to eat at least two portions of fish each week—and one of them should be an oily fish such as salmon or albacore tuna.

Pregnant people should not eat raw fish or seafood, notes Asima Ahmad, MD, a reproductive endocrinologist, obstetrician and gynecologist and co-founder of Carrot Fertility. “This is to avoid exposure to certain bacteria and parasites, including listeria,” she notes.

Dr. Ahmad, who was not involved with the research, says there are still many options for pregnant women to consume. Safe fish to eat during pregnancy include salmon, albacore tuna, mackerel, anchovies, cod and trout, just to name a few.

“Although there has been advice warning against certain types of fish, there is no evidence to support there being any adverse effects,” Dr. Golding says.

Dr. Golding hopes the study results will influence the way in which the overall recommendations are written.

“They should be promoting the positive effects without any misleading caveats,” she says. “Omit all warnings that certain fish should not be eaten.”

Because the world tends to follow what the U.S. does with medical recommendations, Dr. Golding hopes America will take the lead.

But Dr. Ahmad tells Motherly that she doesn’t believe this study will be enough to change the guidance.

“I think if similar studies are completed in different regions of the world with different populations, and yet continue to have the same findings, there is a higher likelihood that recommendations may change,” says Dr. Ahmad.

In the meantime, don’t get discouraged or bogged down by conflicting information. Women should not think they should continue to limit or avoid seafood consumption when pregnant because the study is just one more source of “endless inconsistency and confusion on this general subject,” Phil Spiller, former director of the Office of Seafood at the FDA, tells Motherly. (He wasn’t affiliated with the study.)

“Dr. Golding’s analysis and the conclusions she and her colleagues present are the real deal and pregnant women and their healthcare providers need to understand that,” he adds.

Sources

Golding J, et al. The benefits of fish intake: Results concerning prenatal mercury exposure and child outcomes from the ALSPAC prebirth cohort. NeuroToxicology. 2022.

Simione M, et al. Maternal fish consumption in pregnancy is associated with a bifidobacterium-dominant microbiome profile in infants. 2020. Current Developments in Nutrition.

Snetselaar L, et al. Seafood Consumption during Pregnancy and Lactation and Neurocognitive Development in the Child: A Systematic Review. USDA Nutrition Evidence Systematic Review. 2020.