Researchers studied how extra folic acid in the diet affects the brain after a stroke-like event. Using fruit flies as a model, they found that flies eating high levels of folic acid had worse survival rates and struggled to move normally after experiencing low oxygen (similar to what happens during a stroke). While folic acid is normally healthy, this study suggests that getting too much—which is becoming more common in the U.S.—might actually be harmful when the brain doesn’t have enough oxygen. The findings raise important questions about recommended folic acid intake levels.

The Quick Take

  • What they studied: Whether eating too much folic acid (a B vitamin) affects how well the brain recovers after experiencing low oxygen, similar to what happens during a stroke.
  • Who participated: Adult male and female fruit flies (Drosophila melanogaster), a common research model organism. Some flies ate normal amounts of folic acid, while others ate 100 times the normal level.
  • Key finding: Flies that ate high levels of folic acid had higher death rates after low oxygen exposure and showed reduced ability to climb and move normally compared to flies eating normal amounts. This suggests too much folic acid might interfere with brain recovery.
  • What it means for you: This research suggests that while folic acid is important for health, consuming excessive amounts—which is increasingly common in the U.S. due to fortified foods—might be harmful, especially for brain health. However, this is early research in fruit flies and doesn’t yet mean people should change their folic acid intake without talking to a doctor.

The Research Details

Scientists used fruit flies as a model to study how high dietary folic acid affects the brain during and after low oxygen conditions. They divided flies into two groups: one eating a normal diet and another eating a diet with very high folic acid levels (100 times higher). Both groups were then exposed to two hours of low oxygen conditions, similar to what happens during a stroke. The researchers then measured how many flies survived, how well they could move and climb, and examined their brain tissue for damage.

The researchers used advanced laboratory techniques to confirm that the high-folic-acid group actually had much higher levels of folic acid in their bodies. They also tested whether the folic acid caused direct damage to brain cells, which it didn’t appear to do in the way they measured it.

This type of study using fruit flies is valuable because fruit flies have similar basic brain functions to humans, making them useful for understanding how nutrients affect brain health. However, findings in fruit flies don’t automatically apply to humans.

This research approach is important because it allows scientists to carefully control diet and environmental conditions in ways that would be impossible in human studies. By using a simple organism like fruit flies, researchers can identify potential problems with nutrient levels before testing in humans. The study specifically looked at a real health problem—strokes are becoming more common as people age—and examined a modifiable factor (diet) that could be changed.

This study has several strengths: it tested both male and female flies to see if sex matters, it used precise laboratory methods to measure folic acid levels, and it examined multiple outcomes (survival, movement, and brain tissue). However, the study doesn’t specify exactly how many flies were tested, which makes it harder to judge the reliability of the results. The findings are preliminary and come from fruit flies, not humans, so they need to be confirmed in further research before drawing firm conclusions about human health.

What the Results Show

The most striking finding was that flies eating high levels of folic acid had significantly higher death rates after experiencing low oxygen compared to flies eating normal amounts. This suggests that excess folic acid might make the brain more vulnerable to damage from lack of oxygen.

After the low oxygen exposure, the high-folic-acid flies also showed reduced motivation to climb. When researchers tested their climbing ability, these flies were less likely to attempt climbing compared to control flies. This behavioral change suggests that excess folic acid might affect brain function related to motivation or movement control.

Interestingly, when the high-folic-acid flies were in normal oxygen conditions (not stressed), they actually moved faster when descending during climbing tasks. This suggests that excess folic acid affects how the brain works in different situations—it might enhance some functions while harming others.

When researchers examined brain tissue after the low oxygen exposure, they didn’t find increased cell death in the high-folic-acid group compared to controls. This was surprising and suggests that the harmful effects of excess folic acid might work through a different mechanism than direct brain cell damage.

The study confirmed that the flies actually experienced the low oxygen exposure by observing escape behaviors in larvae. The researchers also successfully demonstrated that the high-folic-acid diet actually increased folic acid levels in the flies’ bodies, confirming the diet worked as intended. The fact that excess folic acid affected behavior and survival but not obvious brain cell death suggests the vitamin might be interfering with how brain cells communicate or function, rather than killing them directly.

This research adds to growing concerns about excessive folic acid intake in modern diets. While folic acid is essential for health and preventing birth defects, many foods in the U.S. are fortified with it, and some people take supplements, leading to intake levels well above recommended amounts. Previous research has suggested that too much folic acid might have unexpected negative effects, but this is one of the first studies specifically examining how excess folic acid affects the brain during oxygen deprivation, which is relevant to stroke risk.

The study uses fruit flies, not humans, so the results may not directly apply to people. The exact number of flies tested isn’t specified, making it difficult to assess how reliable the findings are. The study only looked at one specific high dose of folic acid (100 times normal), so it’s unclear how different amounts might affect outcomes. The research examined only short-term effects (24 hours after low oxygen), so long-term impacts are unknown. Additionally, the study didn’t explore why excess folic acid causes these problems, only that it does.

The Bottom Line

Based on this preliminary research, people should be cautious about consuming folic acid levels significantly above recommended amounts. The recommended daily intake for adults is 400 micrograms. Rather than taking high-dose supplements or consuming excessive fortified foods, aim for the recommended amount through a balanced diet. If you’re concerned about your folic acid intake or have had a stroke, discuss your diet with your doctor before making changes. This research is early-stage and shouldn’t prompt immediate dietary changes without professional guidance.

This research is most relevant to people concerned about stroke risk, older adults (since stroke risk increases with age), people taking folic acid supplements, and those with family histories of stroke. People with obesity or other stroke risk factors should pay attention to this research as it develops. However, pregnant women and those planning pregnancy should continue taking folic acid as recommended by their doctors, since folic acid is crucial for preventing birth defects. This research shouldn’t change medical recommendations for any group without further human studies.

This is very early research, so it’s too soon to expect any changes in health recommendations. It typically takes 5-10 years of additional research to move from fruit fly studies to human applications. Realistic expectations are that this finding will prompt further investigation in animal models and eventually human studies, but changes to dietary guidelines would only come after substantial additional evidence.

Want to Apply This Research?

  • Track daily folic acid intake from all sources (supplements, fortified cereals, leafy greens, legumes) and compare against the recommended daily amount of 400 micrograms. Log whether intake is below, at, or above recommendations.
  • Review all supplements and fortified foods you consume and identify which ones contain folic acid. Consider whether you’re getting folic acid from multiple sources that together exceed recommended amounts. If so, work with a healthcare provider to adjust your intake to recommended levels.
  • Monthly check-ins to review folic acid sources and ensure intake stays within recommended ranges. For those with stroke risk factors, track this alongside other dietary factors like sodium, saturated fat, and overall nutrition quality. Share results with your healthcare provider during regular check-ups.

This research is preliminary, conducted in fruit flies, and has not been tested in humans. The findings do not yet warrant changes to current medical recommendations or folic acid intake guidelines. Folic acid remains essential for health, particularly for pregnant women and those planning pregnancy. Do not change your folic acid intake or supplementation without consulting your healthcare provider. If you have concerns about stroke risk or your current diet, speak with a doctor or registered dietitian. This article is for educational purposes and should not be considered medical advice.