Researchers used advanced genetic analysis to investigate whether vitamin levels actually cause infections, or if infections change vitamin levels. They studied data from hundreds of thousands of people and found that higher vitamin E levels may increase the risk of viral infections, while bacterial infections appear to lower vitamin D levels. They also confirmed these findings in mice with severe infections. This research helps clarify a confusing question: does having certain vitamin levels make you more likely to get sick, or does getting sick change your vitamin levels?

The Quick Take

  • What they studied: Whether vitamin levels in your blood actually cause infections, or if infections change your vitamin levels. They looked at seven different vitamins and two types of infections: bacterial and viral.
  • Who participated: The study analyzed genetic information from hundreds of thousands of people of European ancestry in the UK Biobank and Finnish health databases. Researchers also tested mice with severe infections to confirm their findings.
  • Key finding: Higher vitamin E levels were linked to a 45% increased risk of viral infections. People with bacterial infections had lower vitamin D levels. When mice developed severe infections, their vitamin D levels dropped by about half.
  • What it means for you: This suggests that very high vitamin E levels might not protect you from viral infections as previously thought, and that bacterial infections may use up your vitamin D. However, this doesn’t mean you should avoid vitamin E—more research is needed to understand what these findings mean for healthy people taking supplements.

The Research Details

This study used a special genetic method called Mendelian randomization, which is like a detective tool for figuring out cause-and-effect relationships. Instead of just watching people and seeing who gets sick, researchers used genetic information to trace whether vitamin levels actually cause infections or vice versa. They analyzed genetic data from hundreds of thousands of people stored in large health databases. The researchers looked at genes that naturally make some people have higher or lower vitamin levels, then checked if those same genes were connected to infection risk. This approach is powerful because genes are randomly inherited and can’t be changed by getting sick, so it helps prove what causes what. To make their findings stronger, the researchers also did experiments with mice that had severe infections. They measured how the mice’s vitamin D levels changed during the infection.

Regular studies can’t easily prove whether vitamins cause infections or infections cause low vitamins, because both things happen together. This genetic approach cuts through that confusion by using nature’s random assignment of genes as a natural experiment. The mouse experiments add real-world proof that infections actually do lower vitamin D levels.

This study is strong because it used genetic data from very large populations (hundreds of thousands of people), which makes the findings more reliable. The researchers tested their results multiple ways to make sure they weren’t just flukes. They also confirmed key findings in living mice, which adds credibility. However, the study only included people of European ancestry, so results might differ in other populations. The mouse experiments used a specific type of infection model, so results might not apply to all types of infections.

What the Results Show

The most striking finding was about vitamin E: people with genetically higher vitamin E levels had a 45% increased risk of getting viral infections. This was unexpected because vitamin E is often promoted as an immune booster. The researchers found this relationship was statistically significant, meaning it’s unlikely to be due to chance. In the opposite direction, people who developed bacterial infections had lower vitamin D levels. This makes sense because the infection itself may deplete vitamin D from the body. The mouse experiments strongly supported this: when mice developed severe infections from bacteria, their vitamin D levels dropped from about 91 units down to 48 units—nearly a 50% decrease. This dramatic drop in mice confirms that serious infections genuinely lower vitamin D levels in the body.

The study found no causal relationships between infections and vitamins A, B6, B12, or C. This means these vitamins don’t appear to cause infections, and infections don’t seem to significantly change their levels. The researchers tested both directions of causality—whether vitamins cause infections and whether infections cause vitamin changes—for all seven vitamins studied.

Previous research has shown that people with infections often have low vitamin D levels, but it wasn’t clear if low vitamin D made them more likely to get infected or if the infection caused the vitamin D to drop. This study suggests the infection causes the drop, not the other way around. The finding about vitamin E is more surprising and contradicts some popular beliefs that high vitamin E always protects against infections. This suggests the relationship between vitamin E and viral infections is more complex than previously thought.

The study only included people with European ancestry, so the findings might not apply equally to other ethnic groups who may have different genetic patterns. The research used genetic data, which is powerful but can’t capture everything about real-life vitamin intake or infection exposure. The mouse experiments used one specific type of severe infection model, so results might differ with other types of infections. The study shows associations and potential causes, but can’t prove 100% certainty about how vitamins and infections interact in every person.

The Bottom Line

Based on this research, there’s no strong evidence that you should change your normal vitamin intake to prevent infections. The vitamin E finding is interesting but preliminary—it doesn’t mean you should avoid vitamin E entirely. If you have a bacterial infection, expect your vitamin D levels to naturally drop during the illness; this appears to be a normal response. If you’re concerned about vitamin D levels, especially after infection, talk to your doctor about testing. For most people, maintaining normal vitamin levels through a balanced diet remains the best approach. (Confidence level: Moderate—more research is needed before making major changes)

This research is most relevant to people who take high-dose vitamin supplements, especially vitamin E. People with recurrent infections might benefit from discussing vitamin D levels with their doctor. Healthcare providers should be aware that infections naturally lower vitamin D, so low levels during or after infection may not indicate a deficiency. People of European ancestry are most directly represented in this study; others should wait for research in their populations.

If you have a bacterial infection, vitamin D levels typically drop during the acute illness and may take weeks to months to recover after the infection clears. You won’t see immediate changes from adjusting vitamin intake, as the body maintains relatively stable vitamin levels. If you’re concerned about vitamin levels, testing should happen when you’re healthy, not during an active infection.

Want to Apply This Research?

  • Track vitamin D levels quarterly through blood tests, especially if you have recurrent infections. Note the timing of infections and any vitamin D testing to see if your levels drop during or after illness.
  • If you take high-dose vitamin E supplements, consider discussing with your doctor whether you need that level, especially if you’re prone to viral infections. For bacterial infections, don’t be alarmed if vitamin D testing shows low levels during or immediately after illness—this appears to be a normal response.
  • Maintain a simple log of infections (type and duration) and any vitamin D test results. Over time, this helps you and your doctor see patterns in how infections affect your vitamin levels and whether supplementation helps recovery.

This research provides genetic evidence about relationships between vitamins and infections but should not replace medical advice from your healthcare provider. The findings are preliminary and based on population-level data—individual responses to vitamins vary greatly. Do not change your vitamin supplementation or medical treatment based solely on this study. If you have recurrent infections or concerns about vitamin levels, consult your doctor for personalized testing and recommendations. This study was conducted in people of European ancestry; results may not apply equally to other populations. Always discuss supplement use with your healthcare provider, especially if you take high-dose vitamins or have chronic health conditions.