Researchers wanted to know if eating plant stanols—special compounds found in some foods—could help older people’s bodies respond better to flu vaccines. They gave 128 people aged 59-87 different amounts of plant stanols (or a placebo) for two weeks before and four weeks after getting a flu shot. While the plant stanols did lower cholesterol levels, they didn’t improve how well people’s immune systems responded to the vaccine. This suggests that plant stanols may help your heart health but won’t make your flu shot more effective.

The Quick Take

  • What they studied: Whether eating plant stanols (compounds that lower cholesterol) could help older adults’ immune systems respond better to flu vaccines
  • Who participated: 128 healthy older adults between ages 59 and 87, split into four groups: three groups received different amounts of plant stanols (2, 3, or 4 grams daily), and one group received a placebo (fake product)
  • Key finding: Plant stanols did not improve immune responses to the flu vaccine, even though they successfully lowered cholesterol levels. The groups that received plant stanols had similar antibody responses to the flu vaccine as the control group.
  • What it means for you: If you’re an older adult considering plant stanols for immune health, this study suggests they won’t make your flu shot work better. However, they may still be worth taking for cholesterol management—talk to your doctor about whether they’re right for you.

The Research Details

This was a double-blind, randomized controlled trial, which is considered one of the strongest types of medical research. Participants were randomly assigned to receive either plant stanols or a placebo, and neither the participants nor the researchers knew who was getting which product until the study ended. This prevents bias from affecting the results.

Participants consumed their assigned product for about two weeks before getting their annual flu vaccine, then continued taking it for four weeks after vaccination. The researchers measured antibody levels (the immune system’s defense proteins) at different time points to see how well each person’s body responded to the vaccine. They also checked cholesterol levels and other blood markers to see if the plant stanols had other effects.

This research design is important because it helps prove cause-and-effect relationships. By randomly assigning people to groups and keeping everyone (including doctors) blind to who got what, the researchers could be confident that any differences between groups were due to the plant stanols themselves, not other factors. This type of study is much stronger evidence than simply observing what happens when people choose to eat plant stanols.

This study has several strengths: it included a good number of participants (128), used a proper control group, was double-blinded, and measured multiple immune markers. However, the study only lasted about 6 weeks total, so we don’t know if longer-term use might have different effects. The participants were also relatively healthy older adults, so results might differ for people with certain health conditions.

What the Results Show

The main finding was that plant stanols did not improve how well people’s immune systems responded to the flu vaccine. The researchers measured antibody levels (IgM and IgG) and special flu-fighting antibodies called HI antibodies. None of these showed significant improvements in the groups taking plant stanols compared to the placebo group, regardless of whether people took 2, 3, or 4 grams daily.

Interestingly, the plant stanols did work as expected for cholesterol. People taking 3 or 4 grams daily had significantly lower LDL cholesterol (the ‘bad’ cholesterol) compared to the placebo group. The 2-gram group also showed lower cholesterol, but the difference wasn’t quite large enough to be statistically significant.

The researchers also checked various blood cell counts and other immune markers, and found no meaningful differences between the groups. This suggests that plant stanols don’t appear to boost immune function in ways that would help fight off the flu virus.

While the study’s main focus was on immune response, the cholesterol-lowering effect is noteworthy. This confirms that plant stanols work as intended for heart health, even in older adults. The fact that cholesterol improved while immune response didn’t suggests these compounds have specific effects on cholesterol metabolism but don’t broadly enhance immune function.

The researchers mentioned that previous studies showed 4 grams of plant stanols improved antibody responses to other vaccines. This new study is surprising because it suggests that benefit might not apply to flu vaccines specifically, or that the effect might be smaller than previously thought. This highlights how different vaccines and different compounds can interact in unexpected ways.

The study only lasted about 6 weeks, so we don’t know if longer use might eventually help. The participants were relatively healthy older adults, so results might be different for people with weakened immune systems or certain diseases. The study only looked at one flu season, and flu vaccines change yearly, so results might vary in other years. Additionally, the study measured immune response in the lab but didn’t track whether people actually got fewer flu infections in real life.

The Bottom Line

Based on this study, plant stanols are not recommended specifically to improve flu vaccine effectiveness. However, if your doctor recommends them for cholesterol management, they appear safe and effective for that purpose. The evidence suggests they won’t hurt your immune response, but they also won’t enhance it. (Confidence level: Moderate—based on one well-designed study)

This research is most relevant to older adults (60+) considering plant stanols for immune health. People interested in cholesterol management should note that plant stanols do work for that purpose. People with compromised immune systems should not assume plant stanols will help them—they should consult their doctor about proven immune-boosting strategies.

If you’re taking plant stanols for cholesterol, you might see improvements within a few weeks. However, don’t expect them to make your flu shot more effective—the benefits appear to be limited to cholesterol management.

Want to Apply This Research?

  • Track daily plant stanol intake (in grams) alongside cholesterol levels if you’re taking them for heart health. Note the date of flu vaccination and any flu-like symptoms experienced in the following weeks to monitor real-world vaccine effectiveness.
  • If using a nutrition app, log plant stanol-containing foods or supplements daily. Set a reminder to maintain consistent intake if taking them for cholesterol management. Don’t increase intake expecting immune benefits—stick to recommended doses.
  • Monitor cholesterol levels through regular blood tests if taking plant stanols for heart health. Track any illness patterns over flu season, but understand that plant stanols won’t change your vaccine’s effectiveness. Focus on other proven immune strategies like sleep, exercise, and handwashing.

This research suggests plant stanols don’t improve flu vaccine effectiveness in older adults, though they may help with cholesterol. This study does not replace medical advice from your doctor. Before starting plant stanols or changing your vaccination or supplement routine, consult with your healthcare provider, especially if you take medications or have existing health conditions. This single study provides evidence but should be considered alongside other research and your personal health situation.