Researchers looked at vitamin D levels in Americans from 2007 to 2023 using data from a large national health survey. They found that fewer people have low vitamin D levels than before, which is good news. However, they also discovered that more people are taking vitamin D supplements, and some are getting too much vitamin D in their bodies. The study shows that while vitamin D deficiency is becoming less common, too much vitamin D from supplements is becoming more common, especially among people taking multiple supplements.

The Quick Take

  • What they studied: How vitamin D levels in Americans have changed over 16 years and whether taking vitamin D supplements affects these levels
  • Who participated: Thousands of Americans of all ages (1 year and older) who participated in the National Health and Nutrition Examination Survey, a large government health study that tracks Americans’ health
  • Key finding: The percentage of people with low vitamin D dropped from 18.8% to 15.6%, but the percentage with very high vitamin D levels jumped from 2.2% to 7.6%. People taking vitamin D supplements showed even bigger increases in high vitamin D levels, especially those taking 2 or more supplements
  • What it means for you: While low vitamin D is becoming less common (which is good), more people are now getting too much vitamin D from supplements. If you take vitamin D supplements, you may want to check with your doctor about whether you need them and in what amount, since getting too much can also cause health problems

The Research Details

Researchers analyzed information collected from a large, ongoing government health survey called NHANES (National Health and Nutrition Examination Survey) that has been tracking Americans’ health since the 1960s. They looked at blood test results measuring vitamin D levels from 2007 through 2023—a 16-year period. They grouped people into three categories: those with low vitamin D (at risk), those with adequate vitamin D (just right), and those with high vitamin D (may be of concern). They also asked people whether they took vitamin D supplements in the past month.

The researchers adjusted their findings to account for the fact that vitamin D levels naturally change with the seasons—people have higher levels in summer and lower levels in winter. This helped them see the true trends without the seasonal changes getting in the way. They looked at the overall population and also separately examined people who took one supplement, two supplements, or more than two supplements containing vitamin D.

This research approach is important because it shows real-world trends in a large, representative group of Americans rather than just looking at one small group of people. By tracking changes over 16 years, researchers can see whether vitamin D status is actually improving or getting worse. The fact that they separated people by supplement use helps us understand whether the changes are happening naturally or because more people are taking supplements.

This study is reliable because it uses data from NHANES, which is a well-respected government survey that carefully selects a representative sample of Americans. The large number of participants makes the findings more trustworthy. However, the study only shows what’s happening (trends) rather than proving that supplements caused the changes. Also, people self-reported their supplement use, which means some might have forgotten or been inaccurate about what they took.

What the Results Show

From 2007-2008 to 2021-2023, the percentage of Americans with low vitamin D levels decreased from about 19% to about 16%. This is good news because vitamin D is important for bone health and immune function. At the same time, the percentage of people with very high vitamin D levels more than tripled, going from 2.2% to 7.6%.

The changes were even more dramatic among people taking vitamin D supplements. Those taking one supplement had their low vitamin D rate drop from 12.8% to 5.8%, but their high vitamin D rate jumped from 2% to 11.4%. People taking two or more supplements showed the biggest increase in high vitamin D levels, jumping from 4.7% to 30.6%.

This pattern suggests that as more Americans have started taking vitamin D supplements (possibly because of increased awareness about vitamin D’s importance), the overall vitamin D levels in the population have shifted upward. While this has helped reduce deficiency, it has also created a new problem: too many people now have vitamin D levels that are too high.

The study found that the trend toward higher vitamin D levels was consistent across the entire time period studied, showing this is a gradual, ongoing change rather than a sudden shift. The biggest increases in high vitamin D levels occurred among supplement users, suggesting that supplements are the main driver of the increase in high vitamin D levels rather than dietary sources or sun exposure.

Previous research has shown that vitamin D deficiency was a significant public health problem in the United States, with many people not getting enough. This study confirms that the situation has improved, likely due to increased awareness and more people taking supplements. However, earlier research also warned that too much vitamin D can cause problems like kidney stones and high calcium levels in the blood. This new study shows that we may be shifting from one problem (too little vitamin D) to another problem (too much vitamin D from supplements).

The study only shows what’s happening with vitamin D levels over time—it doesn’t prove that supplements caused the changes, though it strongly suggests they did. People reported their own supplement use, which might not be completely accurate. The study also doesn’t tell us whether the high vitamin D levels are actually causing health problems in these people. Additionally, the study doesn’t explain why some people are taking multiple vitamin D supplements or whether they’re doing so on doctor’s advice.

The Bottom Line

If you take vitamin D supplements, talk to your doctor about whether you actually need them and what dose is right for you. Don’t assume that more is better—too much vitamin D can be harmful. If you’re concerned about your vitamin D level, ask your doctor for a blood test rather than just starting supplements on your own. For most people, getting vitamin D from food sources (like fatty fish, egg yolks, and fortified milk) and moderate sun exposure is safer than taking high-dose supplements.

Everyone should be aware of this trend, but it’s especially important for people who are already taking vitamin D supplements or considering starting them. People at higher risk for vitamin D deficiency (such as those with limited sun exposure, darker skin tones, or certain medical conditions) should work with their doctor to find the right balance. Older adults and people with kidney disease should be particularly careful about vitamin D levels, as they’re more vulnerable to problems from both too little and too much.

If you’re taking vitamin D supplements and want to check your levels, it typically takes 2-3 months for blood levels to change noticeably after changing your supplement dose. If your doctor recommends stopping or reducing supplements, you might not see changes in how you feel immediately, but your blood levels should adjust within a few months.

Want to Apply This Research?

  • Track your daily vitamin D supplement intake (dose and number of supplements) and note any symptoms like nausea, weakness, or excessive thirst that could indicate too much vitamin D. Record the date of any vitamin D blood tests and the results to monitor your actual levels over time.
  • Instead of automatically taking vitamin D supplements, use the app to log your sun exposure time, vitamin D-rich foods you eat, and any symptoms. Share this information with your doctor to determine if you actually need supplements and at what dose. If you do take supplements, use the app to set a reminder to take only the recommended dose rather than multiple supplements.
  • Set up quarterly reminders to review your vitamin D supplement use with your doctor. Track any changes in how you feel and log the results of any blood tests. Use the app to identify patterns between your supplement use, sun exposure, diet, and any symptoms you experience. This long-term tracking will help you and your doctor determine the right vitamin D strategy for your individual needs.

This research shows trends in vitamin D levels but does not provide personalized medical advice. Vitamin D needs vary greatly between individuals based on age, skin tone, location, medical conditions, and medications. Do not start, stop, or change vitamin D supplements without consulting your healthcare provider. Too much vitamin D can cause serious health problems including kidney damage and high blood calcium levels. If you have concerns about your vitamin D level, ask your doctor for a blood test and personalized recommendations rather than self-treating with supplements.