Eating More Fish May Be Linked to Lower Risk of High Blood Pressure During Pregnancy, Researchers Find

Pregnancy-related high blood pressure, an umbrella term that includes gestational hypertension and preeclampsia, affects roughly 5% to 10% of pregnancies worldwide and can have serious consequences for mothers and babies.

Whether eating fish could change a woman’s chances is a question researchers have circled for a while, with little to show for it so far.

A new study from Japan, published in the European Journal of Nutrition, took a different approach. Earlier work looked at what women ate while pregnant. This team also asked about the year before pregnancy began, and the two time windows pointed to different results.

The standout result concerns timing, and the researchers are clear about what it can and can’t show. There’s also a wrinkle involving omega-3s, the nutrient that first drew the team to fish, and it makes the explanation far less obvious than it sounds.

The Number That Stood Out

Eating more fish in the year before pregnancy was linked to lower odds of one particular complication.

The study, published September 8, draws on the Japan Environment and Children’s Study, a nationwide birth cohort of 86,009 women. Researchers sorted the women into five groups by fish intake and compared how likely each group was to develop hypertensive disorders, separating early-onset cases from late-onset ones.

Women in the highest pre-pregnancy fish group had 34% lower odds of early-onset disease than women in the lowest. Odds compare groups against each other, so the figure can’t be read as a third of cases avoided.

The pattern looked stronger among women in their first pregnancy, who had 43% lower odds of early-onset disease with higher pre-pregnancy intake. The release doesn’t say which intake group produced that figure. Among women who had given birth before, the associations weren’t statistically significant, leaving the question open.

Pregnancy Told A Different Story

Once women were pregnant, the associations moved to different outcomes.

Researchers reassessed fish intake in mid-to-late pregnancy, and the associations changed. Higher intake during pregnancy was linked to 14% lower odds of hypertensive disorders when all types were counted together. That figure came from the fourth of five intake groups, not the top one, so the numbers don’t add up to a simple more-is-better rule.

Among women in their first pregnancy, higher intake during pregnancy was also tied to 21% lower odds of late-onset disease.

Why would timing matter? One possible explanation is that early-onset cases often involve problems in the blood vessels that supply the placenta. In contrast, later-onset cases track more closely with the mother’s health and metabolism. Blood-vessel function and inflammation are the suspected links, though the researchers didn’t test that idea directly.

Women also tended to eat less fish once pregnant, which could partly explain why the during-pregnancy results looked different. How big that drop was remains unclear.

Related: 15 Ways to Think About Pregnancy That Show Just How Crazy the Human Body Really Is

Omega-3s Weren’t The Obvious Answer

The nutrient that inspired the research didn’t track with the outcomes as closely as fish did.

Fish is a source of long-chain omega-3 fatty acids, which are linked to vascular health partly through their anti-inflammatory effects. The team tracked omega-3 and omega-6 intake alongside fish.

The fatty-acid numbers didn’t line up as neatly. Total omega-3 intake showed weaker, less consistent associations with hypertensive disorders than fish did, and the researchers say total omega-3 intake alone may not explain the fish link.

The study can’t credit omega-3s, or any single nutrient, for the result. What else about eating fish might be involved remains unclear, and nothing in the findings shows that fish oil supplements would produce the same association.

The Question This Leaves Open

The timing finding raises a bigger question than the numbers can answer.

If the pre-pregnancy result holds up, diet before conception could deserve more attention alongside what women eat once they’re expecting. The release frames the findings as support for further research, but it still lacks practical details.

The release doesn’t say how many grams or servings put a woman in the top intake group, which fish and preparation methods counted, or how many women developed each type of disorder. It also doesn’t set an ideal amount of fish or address whether the results hold outside Japan.

Answering the bigger question would take intervention trials that control how much fish women eat, according to the researchers. No such trial has been announced.

Did anyone talk to you about what to eat before you were pregnant, or did the advice only start afterward?

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