Australian researchers found that after the country started adding folic acid to bread and cereals, pregnant women developed gestational diabetes three times more often. The study compared over 2,400 women before and after this food fortification began. Women with very high folate levels in their blood were 48% more likely to develop pregnancy diabetes. The researchers think excess folic acid might affect pregnancy hormones that control blood sugar, though more research is needed to confirm this connection.

The Quick Take

  • What they studied: Whether mandatory folic acid added to foods increases the risk of gestational diabetes in pregnant women
  • Who participated: 2,464 pregnant women in Australia - 1,164 before folic acid was added to foods and 1,300 after
  • Key finding: Gestational diabetes rates tripled from 5% to 15% after folic acid fortification began, and women with very high folate levels had 48% more diabetes cases
  • What it means for you: If you’re pregnant or planning pregnancy, discuss your folic acid intake with your doctor - you may need less supplementation than you think, especially if you eat fortified foods

The Research Details

Researchers compared two groups of pregnant women from the same region in Australia. The first group included women who got pregnant before 2009, when folic acid wasn’t yet added to bread and cereals. The second group included women who got pregnant after 2009, when this fortification became mandatory. Both groups were followed throughout their pregnancies as part of larger health studies. The researchers measured folate levels in the women’s blood early in pregnancy and tracked who developed gestational diabetes. They also measured several pregnancy hormones that help control blood sugar levels.

This natural experiment design is valuable because it shows what happened to a whole population when folic acid fortification was introduced. The researchers could compare the same types of women in the same locations, with the main difference being whether they were exposed to fortified foods or not.

The study followed women prospectively, meaning researchers tracked them forward in time rather than looking backward at medical records. The sample size was large enough to detect meaningful differences, and the researchers controlled for other factors that might affect diabetes risk.

What the Results Show

The most striking finding was that gestational diabetes rates jumped from 5% to 15.2% after folic acid fortification began. At the same time, women’s folate levels increased dramatically - blood folate went up 18% and red blood cell folate increased by 259%. More than half of the women after fortification had folate levels above what’s considered the normal range. The researchers used statistical analysis to suggest that these higher folate levels may have contributed to the increased diabetes risk. Women with excess folate levels had 48% more cases of gestational diabetes compared to women with normal levels.

The study also found that pregnancy hormones changed after fortification. Levels of human placental lactogen increased by 29% and placental growth hormone went up 13%. Women with excess folate had 24% higher prolactin levels and 13% higher placental lactogen levels. These hormones normally help regulate blood sugar during pregnancy, so changes in their levels might explain the link between excess folate and diabetes.

Previous animal studies had suggested that too much folic acid during pregnancy could affect blood sugar control, but this is one of the first large human studies to show a similar pattern. The findings align with concerns some researchers have raised about whether current folic acid recommendations might be too high in countries with food fortification.

This study can’t prove that excess folic acid directly causes gestational diabetes - it only shows an association. Other factors that changed over time in Australia might also contribute to rising diabetes rates. The study was done in one country, so results might not apply everywhere. The researchers also couldn’t control for all possible factors that might affect diabetes risk.

The Bottom Line

If you’re pregnant or planning pregnancy, talk with your healthcare provider about your total folic acid intake from both supplements and fortified foods. You may not need as much supplementation as standard recommendations suggest, especially if you eat bread, cereals, and other fortified foods regularly. Don’t stop taking folic acid entirely, as adequate levels are crucial for preventing birth defects.

This research is most relevant for women in countries with mandatory folic acid food fortification, including the US, Canada, and Australia. Women who eat a lot of fortified foods and take high-dose folic acid supplements should pay particular attention. However, women at high risk for neural tube defects may still need higher doses despite these findings.

Folate levels in blood change within weeks of dietary changes, so adjustments to supplementation could have relatively quick effects. However, more research is needed before major changes to public health recommendations are made.

Want to Apply This Research?

  • Log your daily folic acid intake from both supplements and fortified foods (check labels on bread, cereals, and other grain products)
  • Track your consumption of fortified foods and discuss with your doctor whether you can reduce supplement doses while maintaining adequate folate levels
  • Monitor blood sugar levels if recommended by your healthcare provider, especially if you have high folate intake and other diabetes risk factors

This research suggests an association but doesn’t prove causation. Do not stop taking folic acid supplements without consulting your healthcare provider, as adequate folate is essential for preventing serious birth defects. Individual needs vary, and your doctor can help determine the right amount for your situation.