Researchers studied over 4,500 American adults to understand how vitamin B12 levels relate to testosterone in women and men. They found something surprising: in women, higher vitamin B12 levels were linked to lower testosterone levels. This connection was especially strong in younger women who were overweight. Interestingly, this relationship didn’t show up in men. The findings suggest that vitamin B12’s role in hormone health may work differently depending on whether you’re male or female, and that body weight might play an important role in how these two factors interact.

The Quick Take

  • What they studied: Whether the amount of vitamin B12 in a person’s blood is connected to their testosterone levels, and whether body weight changes this relationship
  • Who participated: 4,571 American adults (about half men, half women) with an average age of 48 years, using health data collected between 2011 and 2014
  • Key finding: In women, each increase in vitamin B12 was linked to a small decrease in testosterone. This pattern was strongest in younger women (ages 20-39) who were overweight. Men showed no clear connection between B12 and testosterone.
  • What it means for you: If you’re a woman, especially a younger woman with extra weight, very high B12 levels might be associated with lower testosterone. However, this doesn’t mean you should avoid B12—it’s still essential for your health. Talk to your doctor about what’s right for you.

The Research Details

This study used information from a large national health survey called NHANES that tracked American adults’ health between 2011 and 2014. Researchers looked at blood test results showing vitamin B12 levels and testosterone levels for over 4,500 people. They used statistical tools to find patterns and connections between these two measurements, while accounting for other factors that might affect the results, like age, race, and overall health.

The researchers created three different analysis models to test their findings. The first model looked at the raw data without adjusting for anything else. The second and third models added in other factors that might influence the relationship, like age, smoking status, and medical conditions. This approach helps researchers see if the B12-testosterone connection is real or if it’s just caused by other factors.

The study also looked at whether body weight (measured as BMI) changed how B12 and testosterone were related. This is important because body weight affects many hormones in the body.

This research approach is valuable because it uses real-world data from thousands of Americans rather than a small group in a lab. This makes the findings more likely to apply to everyday people. By testing the same question three different ways, the researchers could be more confident in their results. Looking at how body weight affects the relationship is also important because it helps explain why the same B12 level might have different effects on different people.

This study has several strengths: it included a large number of people, used standardized blood tests, and carefully adjusted for other factors that could affect the results. However, because this is a snapshot study (not following people over time), we can only see that B12 and testosterone are connected—we can’t prove that B12 causes changes in testosterone. The findings in women are clear, but the lack of findings in men is also important information. The study used data from 2011-2014, so some findings might be different today.

What the Results Show

The main discovery was that in women, higher vitamin B12 levels were linked to lower testosterone levels. This relationship held true even after researchers accounted for age, race, smoking, and other health factors. The connection was small but consistent across all three statistical models tested.

Body weight played an important role in this relationship. In younger women aged 20-39, the connection between B12 and testosterone was much stronger if they were overweight. This suggests that being overweight might amplify how B12 affects testosterone in younger women.

In contrast, men showed no clear relationship between vitamin B12 levels and testosterone. Whether men had high or low B12 didn’t predict their testosterone levels. This gender difference is important because it shows that B12 and testosterone interact differently in male and female bodies.

The study found that the B12-testosterone relationship was strongest in younger women (ages 20-39) rather than older women. This age-specific finding suggests that hormonal changes throughout a woman’s life might affect how B12 and testosterone interact. The modifying effect of body weight was particularly notable in this younger age group, indicating that weight management might be especially important for younger women concerned about hormone balance.

Previous research has suggested that vitamin B12 plays a role in hormone health, but most studies focused on men or didn’t look at gender differences. This study adds important new information by showing that B12’s relationship with testosterone appears to be gender-specific. The finding that body weight modifies this relationship is also relatively new and suggests that future research should consider how multiple factors work together to affect hormones.

This study is a snapshot in time, so we can’t prove that B12 causes testosterone changes—only that they’re connected. The study used data from 2011-2014, which is over a decade old, so current patterns might be different. The researchers measured total testosterone but didn’t look at other forms of testosterone or related hormones that might tell a more complete story. Additionally, the study couldn’t account for all possible factors that affect hormones, such as stress, sleep, or medication use. Finally, while the findings in women are clear, the lack of findings in men needs more research to understand why.

The Bottom Line

Based on this research, there’s no reason to avoid vitamin B12 or reduce your intake if you’re a woman. B12 is essential for nerve function, energy, and DNA health. If you’re a younger woman with extra weight, discuss your B12 and testosterone levels with your doctor—they can help determine what’s normal for you and whether any changes are needed. Don’t make major changes to your B12 intake based on this single study. (Confidence level: Moderate—this is one study and more research is needed)

This research is most relevant to women, particularly younger women (20-39 years old) who are overweight or have concerns about hormone balance. Women experiencing symptoms like irregular periods, low energy, or mood changes should discuss their B12 and hormone levels with a healthcare provider. Men can note that this study didn’t find a B12-testosterone connection for them, but should still maintain adequate B12 for overall health. Anyone considering B12 supplements should talk to their doctor first.

If you make changes based on this research, don’t expect immediate results. Hormone levels change slowly, and it may take several weeks to months to notice any differences. If you’re working with a doctor to adjust B12 intake or address weight, they’ll likely want to recheck your blood levels after 2-3 months to see if anything has changed.

Want to Apply This Research?

  • Track your B12 intake (from food and supplements) and record any changes in energy levels, mood, or menstrual regularity. Note your weight weekly and look for patterns over 8-12 weeks. If using the app with a healthcare provider, share these records at your next appointment.
  • If you’re a younger woman concerned about this research, focus on maintaining a healthy weight through balanced nutrition and regular activity. Ensure you’re getting enough B12 from foods like meat, fish, eggs, and dairy, or take a supplement if recommended by your doctor. Use the app to log B12-rich foods and track weight trends without obsessing over daily fluctuations.
  • Set a reminder to log your B12 intake and weight weekly. Every 3 months, review your trends to see if there are patterns. If you’re working with a doctor, use the app to prepare for appointments by having your data organized. Note any changes in how you feel—energy, mood, or menstrual changes—as these may be related to hormone balance.

This research shows a connection between vitamin B12 and testosterone in women, but it doesn’t prove that B12 causes testosterone changes. This study is observational and cannot establish cause-and-effect. Do not change your B12 intake or hormone treatments based on this research alone. If you have concerns about your B12 levels, testosterone, or hormone balance, consult with a healthcare provider who can evaluate your individual situation, run appropriate tests, and recommend personalized treatment. This information is educational and not a substitute for medical advice.